Experimental Evaluation of PGI, HK, PFK, and G6PDH in Glycolysis and Pentose Phosphate Pathway Branching Analysis
Experimental Evaluation of PGI, HK, PFK, and G6PDH in Glycolysis and Pentose Phosphate Pathway Branching Analysis
After glucose enters cells, it can be converted into pyruvate and lactate through glycolysis, or it can enter the pentose phosphate pathway to generate NADPH and ribose phosphate. HK, PGI, PFK, and G6PDH correspond respectively to glucose phosphorylation after uptake, G6P/F6P interconversion, the committed step of glycolysis, and the entry point of the oxidative branch of the pentose phosphate pathway. They are important enzymatic nodes for evaluating glucose metabolic flux distribution.
Keywords: glycolysis; pentose phosphate pathway; PGI; HK; PFK; G6PDH; NADPH; metabolic branching
1 Core Nodes in Glycolysis and Pentose Phosphate Pathway Branching Analysis
1.1 Key Branch Points After Glucose Entry
(1) HK controls the glucose entry step
Hexokinase (HK) catalyzes the phosphorylation of glucose to generate glucose 6-phosphate (G6P), which is the entry step after glucose enters intracellular metabolism. Increased HK activity usually indicates stronger cellular glucose capture capacity, but whether G6P subsequently enters glycolysis, the pentose phosphate pathway, glycogen synthesis, or other branches still needs to be judged together with downstream indicators.
(2) PGI connects G6P and F6P
Phosphoglucose isomerase (PGI) catalyzes the reversible interconversion between G6P and fructose 6-phosphate (F6P). PGI is located at the interface between glycolysis and the oxidative branch of the pentose phosphate pathway. It affects the movement of G6P toward F6P and also influences whether G6P is retained for the G6PDH reaction.
(3) PFK determines the committed step of glycolysis
Phosphofructokinase (PFK) catalyzes the conversion of F6P into fructose 1,6-bisphosphate (F1,6BP), which is an important rate-limiting and regulatory step in glycolysis. Enhanced PFK activity usually indicates increased commitment to the glycolytic pathway, but its in vivo function is regulated by ATP, AMP, citrate, fructose 2,6-bisphosphate, pH, and other factors. Therefore, in vitro enzyme activity should be interpreted together with the metabolic state.
(4) G6PDH reflects the entry point of the oxidative branch of the pentose phosphate pathway
Glucose-6-phosphate dehydrogenase (G6PDH) catalyzes the oxidation of G6P and generates NADPH. It is the key entry enzyme of the oxidative branch of the pentose phosphate pathway. Increased G6PDH activity usually indicates increased cellular demand for NADPH, reducing power, and nucleotide precursors, but actual flux is also affected by the NADP⁺/NADPH ratio and G6P supply.
Table 1 Key enzymatic nodes in glycolysis and pentose phosphate pathway branching analysis
Enzyme | Catalyzed Reaction | Functional Position | Main Experimental Significance | Interpretation Boundary |
HK | Glucose → G6P | Entry point of glucose metabolism | Evaluates glucose capture and G6P generation capacity | Cannot independently determine the fate of G6P |
PGI | G6P ↔ F6P | Interface between glycolysis and PPP | Evaluates the capacity of G6P conversion toward glycolysis | Reversible reaction; must be interpreted with metabolite ratios |
PFK | F6P → F1,6BP | Committed step of glycolysis | Evaluates the ability to drive downstream glycolysis | Strongly affected by allosteric regulation |
G6PDH | G6P → 6-phosphoglucono-δ-lactone | Entry point of oxidative PPP | Evaluates NADPH generation and PPP entry capacity | Enzyme activity is not equivalent to actual PPP flux |
1.2 Basic Experimental Logic of Branching Analysis
(1) Entry supply
HK activity, glucose consumption, and G6P level together reflect the supply capacity after glucose enters the cell. If HK activity increases but G6P does not accumulate, G6P may be rapidly entering downstream pathways. If G6P increases while PFK or G6PDH shows no obvious enhancement, downstream utilization may be limited.
(2) Glycolytic progression
PGI and PFK jointly determine the efficiency with which G6P is converted toward glycolysis. When PGI increases but PFK remains unchanged, F6P generation capacity may be enhanced, but the committed step of glycolysis may not be enhanced synchronously. When PFK increases together with changes in lactate, pyruvate, or ATP, the evidence for enhanced glycolysis is stronger.
(3) PPP branching
G6PDH activity, 6-phosphogluconate (6PG), ribose 5-phosphate (R5P), the NADPH/NADP⁺ ratio, and oxidative stress indicators together reflect the status of the oxidative branch of the pentose phosphate pathway. If G6PDH increases but NADPH does not increase, enhanced NADPH consumption or insufficient substrate supply should be considered.
(4) Integrated interpretation
Glycolysis/PPP branching should not be summarized simply as “one enzyme is increased.” A more appropriate approach is to use HK to represent glucose entry, PGI and PFK to represent glycolytic pull, and G6PDH to represent oxidative PPP pull, while verifying actual flux with metabolites and isotope tracing.
2 Enzyme Activity Assay Design for Key Enzymes
2.1 Sample Processing and Normalization
(1) Cell samples
Cell enzyme activity assays should be performed after rapid lysis under low-temperature conditions to minimize enzyme inactivation and metabolite degradation. For adherent cells, repeated freeze-thaw cycles should be avoided to reduce enzyme activity loss. Suspension cells should be accurately counted and normalized by cell number, total protein, or cell volume.
(2) Tissue samples
For tissue samples, sampling time, cold ischemia time, and homogenization intensity should be controlled. Samples with high lipid content, high hemoglobin content, or abundant connective tissue may affect colorimetric or UV readings. Sample blanks should be set and clarification conditions should be optimized.
(3) Microbial samples
For bacterial, yeast, and fungal samples, ultrasonic disruption, glass beads, enzymatic digestion, or mechanical disruption should be selected according to cell wall structure. Insufficient lysis can underestimate intracellular enzyme activity, while excessive lysis or temperature increase may inactivate the target enzyme.
(4) Normalization method
Enzyme activity results can be normalized by total protein, cell number, tissue mass, or culture volume. When comparing different treatment groups, the normalization method should be kept consistent, and cell death, reduced protein content, or sample dilution should not be misinterpreted as enzyme activity changes.
2.2 HK Activity Assay
(1) Detection principle
HK catalyzes the reaction between glucose and ATP to generate G6P. Subsequently, G6P generates NADPH in the presence of G6PDH and NADP⁺. The detection system usually evaluates HK activity by monitoring the increase in NADPH absorbance at 340 nm. This method is essentially a coupled reaction, and G6PDH, NADP⁺, and Mg²⁺ must not become limiting factors.
(2) Key parameters
The concentrations of glucose, ATP, Mg²⁺, and the coupling enzyme should be excessive or non-limiting. Endogenous G6P, NADPH, or reducing substances in the sample may increase background signals, so no-glucose, no-ATP, or sample blank controls should be included.
(3) Result interpretation
Increased HK activity indicates enhanced glucose phosphorylation capacity, but it does not directly prove enhanced glycolysis. If HK increases together with PFK activity, lactate release, and glucose consumption, the evidence for enhanced glycolysis is stronger. If HK increases together with G6PDH, NADPH, or 6PG, more G6P may be entering the oxidative branch of the PPP.
2.3 PGI Activity Assay
(1) Detection principle
PGI is usually assayed using F6P as the substrate, which PGI converts into G6P. G6P then generates NADPH through the G6PDH-coupled reaction. The increase in NADPH at 340 nm can be used to evaluate PGI activity. This method also depends on sufficient G6PDH and NADP⁺ supply.
(2) Key parameters
F6P substrate purity, G6PDH coupling efficiency, and sample background are the main control points in PGI detection. If the sample contains high endogenous G6P or G6PDH activity, a no-F6P substrate blank should be included to subtract NADPH generation not derived from PGI.
(3) Result interpretation
Increased PGI activity indicates enhanced G6P/F6P interconversion capacity. However, because the PGI reaction is reversible, PGI activity alone cannot determine the direction of net flux. If PGI increases together with F6P, F1,6BP, and lactate, this supports enhanced glycolytic direction. If G6P, 6PG, and NADPH increase synchronously, enhanced PPP branching should be considered.
2.4 PFK Activity Assay
(1) Detection principle
PFK catalyzes the conversion of F6P and ATP into F1,6BP. Common detection systems use coupled reactions involving aldolase, triose phosphate isomerase, and glycerol-3-phosphate dehydrogenase, leading to NADH consumption, which is monitored as a decrease in absorbance at 340 nm. This reaction chain is relatively long, and coupling enzyme activity and substrate supply must be sufficient.
(2) Key parameters
F6P, ATP, Mg²⁺, coupling enzymes, and NADH concentrations all affect the stability of PFK detection. PFK is regulated by ATP, AMP, citrate, fructose 2,6-bisphosphate, and pH. In vitro assay conditions should clearly define whether the target is maximal enzyme activity, basal enzyme activity, or activity under a specific regulatory condition.
(3) Result interpretation
Increased PFK activity indicates enhanced capacity to drive F6P into downstream glycolysis. If lactate, pyruvate, ATP generation, or ECAR also increases, enhanced glycolysis is further supported. If PFK activity decreases while G6PDH activity increases, more G6P may be diverted toward the oxidative branch of the PPP, or the committed step of glycolysis may be inhibited.
2.5 G6PDH Activity Assay
(1) Detection principle
G6PDH catalyzes the oxidation of G6P and reduces NADP⁺ to NADPH, which is usually detected by monitoring the increase in NADPH absorbance at 340 nm. This method has a relatively direct reaction path and is suitable for evaluating the entry enzyme activity of the oxidative branch of the PPP.
(2) Key parameters
G6P, NADP⁺, Mg²⁺, and sample background must be strictly controlled. If the sample contains 6-phosphogluconate dehydrogenase (6PGDH) activity or other NADP⁺-dependent dehydrogenases, the reading may be affected. No-G6P substrate blanks and heat-inactivated controls should be included.
(3) Result interpretation
Increased G6PDH activity indicates enhanced capacity of the oxidative branch of the PPP. If this is accompanied by increased 6PG, R5P, NADPH/NADP⁺ ratio, or improved oxidative stress tolerance, increased PPP flux is supported. If NADPH does not increase, glutathione reduction, lipid synthesis, or ROS scavenging demand should be considered to evaluate NADPH consumption.
Table 2 Key points for activity assays of PGI, HK, PFK, and G6PDH
Enzyme | Common Detection Method | Main Readout | Required Controls | Interpretation Focus |
HK | G6PDH-coupled method | NADPH increase | No glucose, no ATP, sample blank | Reflects glucose phosphorylation capacity |
PGI | F6P-G6P-G6PDH coupled method | NADPH increase | No F6P, sample blank | Reflects G6P/F6P interconversion capacity |
PFK | Aldolase/TPI/GPDH coupled method | NADH decrease | No F6P, no ATP, coupling system blank | Reflects the capacity of the committed glycolytic step |
G6PDH | NADP⁺ reduction method | NADPH increase | No G6P, sample blank | Reflects the entry capacity of the oxidative PPP branch |
3 Glycolysis and Pentose Phosphate Pathway Branching Analysis
3.1 Enzyme Activity Ratio Analysis
(1) Ratio between HK and downstream enzyme activities
HK represents glucose entry capacity, while PGI, PFK, and G6PDH reflect the subsequent distribution direction of G6P. If HK increases but neither PFK nor G6PDH increases, G6P accumulation, enhanced glycogen synthesis, or changes in other branches should be considered. Synchronous increases in HK and PFK better support enhanced glycolysis, while synchronous increases in HK and G6PDH suggest enhanced PPP entry capacity.
(2) PFK/HK ratio
The PFK/HK ratio can be used to evaluate the relative strength of glucose entering the committed step of glycolysis after entry. An increased PFK/HK ratio suggests enhanced downstream glycolytic pull, while a decreased PFK/HK ratio suggests that G6P or F6P may be retained upstream or diverted into other branches.
(3) G6PDH/HK ratio
The G6PDH/HK ratio reflects the relative capacity of G6P entry into the oxidative branch of the PPP. This ratio often increases under oxidative stress, enhanced lipid synthesis, increased nucleotide synthesis demand, or increased reducing power demand in tumor cells.
(4) G6PDH/PFK ratio
The G6PDH/PFK ratio helps compare the relative tendency between the oxidative branch of the PPP and the committed step of glycolysis. An increased ratio suggests that G6P may be more biased toward NADPH generation and ribose phosphate supply, whereas a decreased ratio suggests stronger glycolytic pull.
Table 3 Combined interpretation of enzyme activity changes in glycolysis and PPP branching
Enzyme Activity Pattern | Possible Indication | Additional Indicators Needed for Validation |
HK↑, PFK↑, G6PDH unchanged | Enhanced glucose entry and glycolytic progression | Lactate, pyruvate, ATP, ECAR |
HK↑, G6PDH↑, PFK unchanged or decreased | Enhanced G6P branching toward the oxidative PPP | 6PG, R5P, NADPH/NADP⁺, ROS |
PGI↑, PFK↑ | Enhanced conversion of G6P toward glycolysis | F6P, F1,6BP, lactate |
PGI decreased, G6PDH↑ | G6P retention or enhanced oxidative PPP | G6P, 6PG, NADPH |
PFK↓, G6PDH↑ | Restricted glycolytic commitment step with relative PPP enhancement | F6P, G6P, 6PG, cellular oxidative stress indicators |
HK↑ but no obvious change in PGI/PFK/G6PDH | Enhanced glucose entry without synchronized downstream utilization | G6P, glycogen, other branch metabolites |
3.2 Combined Metabolite Detection
(1) G6P and F6P
G6P and F6P are located at the front end of the branching point, and their ratio can assist in evaluating PGI reaction status and G6P fate. If G6P increases together with enhanced G6PDH activity, the oxidative branch of the PPP should be emphasized. Increased F6P and F1,6BP more strongly support enhanced glycolytic direction.
(2) F1,6BP and downstream glycolytic intermediates
F1,6BP is the product of the PFK reaction and can be used to determine whether the committed step of glycolysis is being driven forward. If F1,6BP, glyceraldehyde 3-phosphate, phosphoenolpyruvate, pyruvate, and lactate increase synchronously, the evidence for enhanced glycolytic flux is more complete.
(3) 6PG, R5P, and NADPH
6PG and R5P reflect the status of PPP intermediate metabolites, while the NADPH/NADP⁺ ratio reflects reducing power output. If increased G6PDH activity is accompanied by elevated 6PG and NADPH, enhancement of the oxidative PPP is supported. If only G6PDH increases but metabolites do not change, substrate supply, coenzyme limitation, or rapid NADPH consumption should be considered.
(4) Lactate and glucose consumption
Lactate release and glucose consumption are common endpoint indicators in glycolysis evaluation, but they cannot independently explain PPP branching. When increased glucose consumption is accompanied by increased G6PDH activity and NADPH, increased glucose input may be supporting both glycolysis and the PPP.
3.3 Isotope Tracing Analysis
(1) U-¹³C₆-glucose tracing
U-¹³C₆-glucose can be used to observe the overall entry of glucose carbon into glycolysis, the TCA cycle, lactate, ribose phosphate, and amino acid synthesis. This method is suitable for evaluating overall glucose utilization, but distinguishing oxidative PPP from non-oxidative PPP requires specific isotope labeling patterns.
(2) 1,2-¹³C₂-glucose tracing
1,2-¹³C₂-glucose can be used to distinguish the contributions of glycolysis and oxidative PPP in more detail. The oxidative PPP releases glucose C1 as CO₂, thereby changing the labeling patterns of downstream lactate, pyruvate, and ribose phosphate. This strategy is suitable for verifying whether increased G6PDH activity corresponds to increased actual PPP flux.
(3) Isotopologue distribution of metabolites
The isotopologue distribution of metabolites such as lactate, pyruvate, 6PG, R5P, nucleotide ribose, and serine can be used to determine the direction of glucose carbon flow. Measuring endpoint lactate alone is insufficient to explain PPP branching; at minimum, 6PG, R5P, or ribose labeling patterns should be included.
(4) Combined interpretation of tracing and enzyme activity
Enzyme activity assays provide pathway capacity information, while isotope tracing provides actual carbon flux distribution. If G6PDH activity increases and ¹³C tracing shows enhanced labeling of R5P or nucleotide ribose, increased PPP branching is more strongly supported. If enzyme activity increases but isotope branching does not change, substrate, coenzyme, or cellular state limitations should be considered.
4 Application Design in Different Experimental Scenarios
4.1 Glucose Metabolic Reprogramming in Tumor Cells
(1) Evaluation of enhanced glycolysis
Tumor cells often exhibit increased glucose uptake and lactate release. Experiments can detect HK and PFK activities together with glucose consumption, lactate release, ECAR, and glycolytic intermediates. Synchronous increases in HK and PFK accompanied by increased lactate release support enhanced glycolysis.
(2) Evaluation of enhanced PPP
Tumor cells often increase their demand for NADPH and ribose phosphate under rapid proliferation and oxidative stress conditions. G6PDH activity, 6PG, R5P, NADPH/NADP⁺, and nucleotide synthesis-related indicators can be used to evaluate the status of the oxidative PPP.
(3) Evaluation of drug intervention
When glycolytic inhibitors, G6PDH inhibitors, or oxidative stress inducers are used, cell viability, target enzyme activity, metabolites, and ROS should be measured simultaneously. Observing lactate reduction or G6PDH reduction alone cannot exclude non-specific effects caused by cell death or overall metabolic suppression.
4.2 Oxidative Stress and NADPH Demand Analysis
(1) G6PDH response
Under oxidative stress, increased G6PDH activity is usually related to increased demand for NADPH regeneration. If the NADPH/NADP⁺ ratio remains stable while G6PDH increases, NADPH generation and consumption may be enhanced synchronously.
(2) Linkage with antioxidant systems
GSH/GSSG ratio, glutathione reductase activity, ROS levels, and lipid peroxidation products can be analyzed together with G6PDH results. Increased G6PDH accompanied by maintained GSH and decreased ROS more strongly supports the involvement of the PPP in antioxidant defense.
(3) Changes in glycolytic pull
Oxidative stress may inhibit some glycolytic enzymes or alter G6P distribution. If PFK decreases while G6PDH increases, glucose carbon flow may be shifting toward reducing power generation.
4.3 Microbial Fermentation and Metabolic Engineering
(1) Carbon flux distribution
In microbial fermentation, HK or glucokinase reflects glucose entry, PFK reflects glycolytic progression, and G6PDH reflects the oxidative PPP. When the target product depends on NADPH, G6PDH activity and NADPH generation capacity are important evaluation indicators.
(2) Association with product synthesis
Amino acid, nucleotide, lipid, and polysaccharide synthesis differ in their dependence on the PPP and glycolysis. If the target product requires high reducing power, G6PDH activity and the NADPH/NADP⁺ ratio should be used as key evaluation indicators.
(3) Engineering strain screening
When comparing engineered strains, final product yield alone should not be compared. Glucose consumption, major fermentation products, HK/PGI/PFK/G6PDH activities, and key metabolites should be measured together to determine whether metabolic redistribution matches the design goal.
4.4 Regulation of Glucose Metabolism in Plant and Tissue Samples
(1) Source-sink metabolism
In plant tissues, glucose metabolism is affected by developmental stage, light, stress, and tissue type. HK, PGI, PFK, and G6PDH can be used to evaluate sugar input, glycolytic utilization, and PPP branching, but sucrose, starch, G6P, and NADPH-related indicators should also be included.
(2) Stress response
Salt stress, drought, low temperature, and pathogen stimulation can alter the oxidative branch of the PPP to support antioxidant and biosynthetic needs. Increased G6PDH activity accompanied by changes in antioxidant enzyme activity may indicate PPP participation in stress responses.
(3) Sample processing
Plant tissues are rich in polyphenols, polysaccharides, and pigments, which may interfere with colorimetric or UV detection. During sample extraction, appropriate protectants should be added, and sample blanks should be included to avoid the influence of background absorbance on enzyme activity calculation.
5 Common Experimental Misinterpretations and Result Interpretation
5.1 Enzyme Activity Is Not Equivalent to Metabolic Flux
(1) In vitro enzyme activity
In vitro enzyme activity reflects maximal or relative catalytic capacity under specific conditions. The result is affected by substrate, coenzyme, pH, temperature, and inhibitor settings, and it cannot be directly equated with real-time intracellular flux.
(2) In vivo flux
In vivo flux depends on substrate supply, product consumption, coenzyme status, allosteric regulation, cellular compartmentation, and competition from other pathways. Branching analysis should combine enzyme activity with metabolites, coenzyme ratios, and isotope tracing.
(3) Conclusion expression
More accurate wording includes “increased pathway capacity,” “increased enzyme activity related to a specific branch,” or “combined with tracing results, suggesting increased branching.” Avoid using enzyme activity alone to conclude that “flux is increased.”
5.2 Background Interference in Coupled Enzyme Assays
(1) NADPH background
HK, PGI, and G6PDH assays may all involve NADPH readouts. Endogenous NADPH, reducing substances, or other NADP⁺-dependent dehydrogenases in the sample may increase background signals.
(2) NADH background
PFK assays often monitor NADH decrease. Sample turbidity, endogenous oxidoreductase activity, or instability of the coupled system may affect the NADH signal.
(3) Blank settings
No-substrate blank, no-sample blank, coupling system blank, and heat-inactivated sample can be used to identify non-target reactions. Complete blank subtraction is especially important for low-enzyme-activity samples.
5.3 Effect of Cell State on Results
(1) Cell death
When drug treatment causes cell death, decreased enzyme activity may result from reduced cell number or protein degradation rather than specific metabolic pathway inhibition. Cell viability, total protein, and cell number should be measured simultaneously.
(2) Proliferation rate
Rapidly proliferating cells may increase both glycolysis- and PPP-related indicators. Branching analysis should distinguish overall metabolic enhancement from specific branch deviation.
(3) Nutritional conditions
Glucose concentration, glutamine, serum, oxygen concentration, and culture time all affect glucose metabolic status. Culture conditions should be kept consistent among treatment groups or designed as independent experimental variables.
Table 4 Common misinterpretations in evaluating key glucose metabolism enzymes
Misinterpretation | Possible Problem | Optimization Strategy |
Using HK alone to judge enhanced glycolysis | HK only reflects glucose entry | Combine with PFK, lactate, glucose consumption, and ECAR |
Using G6PDH alone to judge PPP flux | G6PDH reflects capacity, not actual carbon flow | Combine with 6PG, R5P, NADPH, and ¹³C tracing |
Ignoring PGI reversibility | PGI activity alone cannot determine net direction | Combine with G6P/F6P and downstream metabolites |
Directly extrapolating in vitro PFK activity to in vivo state | PFK is strongly affected by allosteric regulation | Set regulatory conditions and combine with F1,6BP and lactate |
Not setting sample blanks | Endogenous NAD(P)H affects readings | Set no-substrate and sample blanks |
Replacing flux conclusions with enzyme activity | Enzyme activity and actual flux can differ | Combine metabolomics and isotope tracing |
6 Related Product and Material Selection
Table 5 Products related to key glucose metabolism enzymes and glycolysis/pentose phosphate pathway branching analysis
Application Module | Cat. No. | Product Name | Grade | Application Positioning |
HK activity assay | Hexokinase (HK) Activity Assay Kit (WST-8, Micro Method) | BioReagent | Used to detect HK activity and evaluate glucose phosphorylation capacity and changes at the glucose metabolism entry point | |
HK activity assay | Hexokinase (HK) Activity Assay Kit (UV Colorimetric Method) | BioReagent | Used for HK activity detection in macro-volume systems, suitable for spectrophotometric readings | |
HK activity assay | Hexokinase (HK) Activity Assay Kit (UV Micro Method) | BioReagent | Used for HK activity detection in small samples, suitable for cell, tissue, or low-volume sample analysis | |
HK positive enzyme/method validation | Hexokinase (HK) | Bioactive,Recombinant,ActiBioPure™,High Performance,EnzymoPure™,≥90%(SDS-PAGE),≥150 U/mg enzyme powder; ≥500 U/mg protein | Used for HK reaction system validation, positive control, and establishment of coupled detection methods | |
HK positive enzyme/method validation | Hexokinase from Yeast(Lyophilized) | EnzymoPure™,ActiBioPure™,Bioactive,High Performance,≥150 units/mg protein | Used as a positive enzyme for HK activity assay systems, coupled reactions, and method validation | |
HK positive enzyme/method validation | recombinant Hexokinase | EnzymoPure™, ≥150 units/mg | Used for recombinant HK reaction systems and method validation | |
ADP-dependent HK research | ADP-specific Glucokinase | Bioactive,Recombinant,ActiBioPure™,High Performance,EnzymoPure™,≥90%(SDS-PAGE),Protein concentration: See COA; ≥500 U/mg protein | Used for studying ADP-dependent hexokinase reaction characteristics and validating special glucose metabolism systems | |
PGI/GPI enzymatic validation | Phosphoglucose isomerase (GPI) | ActiBioPure™, Bioactive, High Performance, Recombinant, EnzymoPure™, ≥10,000 U/mL | Used for PGI/GPI reaction system validation and evaluation of G6P/F6P interconversion capacity | |
PGI/GPI enzymatic validation | Phosphoglucose Isomerase (GPI) | ActiBioPure™, Bioactive, High Performance, Recombinant, EnzymoPure™, ≥90% (SDS-PAGE), ≥50 U/mg enzyme powder, ≥100 U/mg protein | Used as PGI/GPI positive enzyme, for method validation, and for establishing G6P/F6P interconversion reactions | |
PGI/GPI enzymatic validation | Phosphoglucose Isomerase (GPI) | ActiBioPure™, Bioactive, High Performance, Recombinant, EnzymoPure™, ≥250 U/mg enzyme powder | Used for PGI/GPI enzymatic reaction validation and early glycolytic conversion studies | |
PFK activity assay | Phosphofructokinase (PFK) Activity Assay Kit (UV Micro Method) | BioReagent | Used to detect PFK activity and evaluate the capacity of F6P entry into the committed step of glycolysis | |
PFK protein expression detection | Human Phosphofructokinase, Muscle (PFKM) ELISA Kit | BioReagent | Used to detect PFKM protein level and support analysis of muscle-type PFK expression changes | |
PFK protein expression detection | Human 6-phosphofructokinase, Liver Type (PFKL) ELISA Kit | BioReagent | Used to detect PFKL protein level and support analysis of liver-type PFK expression changes | |
PFK enzymatic validation | Phosphofructokinase,Bacillus stearothermophilus |
| Used for PFK reaction system validation, positive enzyme control, and substrate conversion studies | |
PFK enzymatic validation | Phosphofructokinase 1 |
| Used for PFK1-related reaction validation and studies of key glycolytic steps | |
G6PD/G6PDH activity assay | Glucose-6-Phosphate Dehydrogenase (G6PDH) Activity Assay Kit (UV Micro Method) | BioReagent | Used to detect G6PDH activity and evaluate the entry capacity of the oxidative branch of the pentose phosphate pathway | |
G6PD/G6PDH activity assay | Glucose-6-Phosphate Dehydrogenase (G6PDH) Activity Assay Kit (UV Colorimetric Method) | BioReagent | Used for G6PDH activity detection in macro colorimetric systems and evaluation of PPP entry enzyme activity | |
G6PD protein expression detection | Human Glucose-6-phosphate Dehydrogenase (G6PD) ELISA Kit | BioReagent | Used to detect human G6PD protein level and support evaluation of expression changes related to the oxidative PPP | |
G6PD protein expression detection | Mouse Glucose 6 Phosphate Dehydrogenase (G6PD) ELISA Kit | BioReagent | Used to detect G6PD protein level in mouse samples, suitable for animal tissue or cell model analysis | |
G6PD/G6PDH positive enzyme/coupling enzyme | Glucose-6-Phosphate Dehydrogenase (G6PD) | ActiBioPure™, Bioactive, High Performance, EnzymoPure™, ≥95%(SDS-PAGE), ≥600 U/mg protein | Used for G6PDH reaction systems, HK/PGI coupled assays, and NADPH generation validation | |
G6PD/G6PDH positive enzyme/coupling enzyme | Glucose-6-phosphate Dehydrogenase from Leuconostoc mesenteroides | EnzymoPure™, ≥200 NADP units/mg protein | Used for G6PDH activity system validation and NADP⁺-dependent reaction detection | |
G6PD/G6PDH positive enzyme/coupling enzyme | Glucose-6-Phosphate Dehydrogenase from Leuconostoc mesenteroides(High-Activity,Suspension) | EnzymoPure™, ≥600 NAD units/mg protein | Used for high-activity G6PDH reaction systems and method validation | |
F6P substrate/intermediate detection | D-Fructose 6-phosphate disodium salt hydrate | ≥95% | Used as a substrate for PGI- and PFK-related reactions and for F6P metabolic node studies | |
F6P substrate/intermediate detection | D-Fructose 6-phosphate dipotassium salt | ≥97% | Used for F6P-related reaction systems, PGI/PFK substrate validation, and early glycolysis analysis | |
F6P substrate/intermediate detection | Fructose-6-Phosphate (F6P) Content Assay Kit (UV Micro Method) | BioReagent | Used to detect F6P content and support evaluation of PGI reaction and PFK substrate supply | |
F6P substrate/intermediate detection | Fructose-6-Phosphate (F6P) Content Assay Kit (UV Colorimetric Method) | BioReagent | Used for F6P content detection in macro systems and analysis of early glycolytic metabolites | |
F1,6BP intermediate | D-Fructose 1,6-bisphosphate trisodium salt octahydrate | ≥98% | Used for PFK product-related experiments, glycolytic intermediate analysis, and method validation | |
Glycolytic endpoint readout | L-Lactic acid (L-LA) Content Assay Kit (WST-8, Micro Method) | BioReagent | Used to detect L-lactate release and support evaluation of downstream glycolytic output | |
Glycolytic endpoint readout | D-Lactic acid (D-LA) Content Assay Kit (WST-8, Micro Method) | BioReagent | Used to detect D-lactate content, suitable for microbial or special lactate metabolism systems | |
Glycolytic endpoint readout | Pyruvic Acid (PA) Content Assay Kit (LDH, Micro Method) | BioReagent | Used for micro-method detection of pyruvate, suitable for cells, tissues, or small-volume samples | |
Glycolytic endpoint readout | Pyruvic Acid (PA) Content Assay Kit (LDH, Colorimetric Method) | BioReagent | Used for colorimetric detection of pyruvate and supports analysis of terminal glycolytic output | |
Soil/environmental glucose metabolism readout | Soil Pyruvate (S-PA) Content Assay Kit (Micro Method) | BioReagent | Used for pyruvate detection in soil samples, suitable for evaluating glucose metabolic activity in environmental samples | |
NADPH standard/coenzyme | NADPH | ≥93% | Used for NADPH-related reaction systems, standards, or reducing power evaluation | |
NADPH standard/coenzyme | NADPH (tetracyclohexanamine) | ≥96% | Used for NADPH standard curves, coenzyme reactions, and method validation | |
NADPH standard/coenzyme | β-Nicotinamide adenine dinucleotide 2′-phosphate reduced tetrasodium salt hydrate（β-NADPHtetrasodium salt hydrate） | ≥97%(HPLC) | Used as NADPH standard, in reducing power detection, and PPP-related experiments | |
NADPH standard/coenzyme | β-Nicotinamide adenine dinucleotide 2′-phosphate reduced tetrasodium salt hydrate（β-NADPHtetrasodium salt hydrate） | ≥99% | Used as a high-purity NADPH standard and in precise enzymatic reaction systems | |
NADPH consumption/redox linkage | NADPH Oxidase Activity Assay Kit (Micro Method) | BioReagent | Used to detect NADPH oxidase activity and support analysis of NADPH consumption and ROS generation | |
NADPH consumption/redox linkage | NADPH Oxidase Activity Assay Kit (Colorimetric Method) | BioReagent | Used for colorimetric evaluation of NADPH oxidase activity and redox status | |
Glutathione/antioxidant linkage | Total Glutathione (T-GSH) Content Assay Kit (DTNB, Micro Method) | BioReagent | Used to detect total glutathione and support evaluation of the NADPH-related antioxidant system | |
Glutathione/antioxidant linkage | Reduced Glutathione (GSH) Content Assay Kit (DTNB, Micro Method) | BioReagent | Used to detect GSH level and evaluate reducing power and antioxidant status | |
Glutathione/antioxidant linkage | Oxidized Glutathione (GSSG) Content Assay Kit (DTNB, Micro Method) | BioReagent | Used to detect GSSG level and support calculation of redox status | |
Glutathione/antioxidant linkage | Glutathione Peroxidase (GSH-Px) Activity Assay Kit (DTNB, Micro Method) | BioReagent | Used to detect GSH-Px activity and support evaluation of the NADPH-GSH antioxidant system |
7 Frequently Asked Questions
7.1 Can G6PDH activity alone be used to determine PPP enhancement?
No. G6PDH activity reflects the entry capacity of the oxidative branch of the PPP, while actual flux is also affected by G6P supply, the NADP⁺/NADPH ratio, and downstream metabolic demand. It should be analyzed together with 6PG, R5P, NADPH/NADP⁺, and isotope tracing.
7.2 Does increased HK activity necessarily indicate enhanced glycolysis?
Not necessarily. Increased HK activity indicates enhanced glucose phosphorylation capacity, but G6P can enter glycolysis, the PPP, glycogen synthesis, or other branches. To determine whether glycolysis is enhanced, PFK activity, lactate release, glucose consumption, and glycolytic intermediates should be measured simultaneously.
7.3 How can PGI activity changes be used in branching analysis?
PGI is located at the G6P/F6P interconversion node. Increased PGI activity can indicate enhanced G6P/F6P interconversion capacity, but because the reaction is reversible, the net branching direction must be judged together with the G6P/F6P ratio, PFK activity, 6PG, and NADPH status.
7.4 Why is PFK suitable as an indicator of the committed step of glycolysis?
PFK catalyzes the conversion of F6P into F1,6BP and is a step strongly affected by energy status and metabolic regulation in glycolysis. Increased PFK activity together with elevated F1,6BP, pyruvate, or lactate more strongly supports enhanced glycolytic progression.
7.5 How should inconsistencies between enzyme activity assays and metabolomics results be interpreted?
Enzyme activity assays reflect catalytic capacity under specific in vitro conditions, while metabolomics reflects the metabolite state at the moment of sampling. When they are inconsistent, substrate supply, coenzyme status, product consumption, sample handling, cell viability, and sampling time differences should be considered.
7.6 Is isotope tracing necessary for analyzing glycolysis and PPP branching?
If the goal is only to screen key enzyme activities or compare pathway capacity, enzyme activity and metabolite detection can be performed first. If the goal is to prove that glucose carbon actually flows into glycolysis or the PPP, ¹³C-glucose tracing is recommended, together with isotopologue distribution analysis of key metabolites.
Combined evaluation of PGI, HK, PFK, and G6PDH can be used to analyze how glucose is distributed between glycolysis and the pentose phosphate pathway after entry into cells. In experimental design, enzyme activity results should be defined as pathway capacity information, and actual flux changes should be verified using metabolites, coenzyme ratios, functional readouts, and isotope tracing. This approach allows more accurate distinction among enhanced glycolysis, increased PPP branching, and elevated overall glucose utilization.
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