Materials and Equipment

Before beginning, ensure the following materials and equipment are available:

• Recombinant Human GPT Protein (SKU: rp364787, Aladdin Scientific)
• Sterile, nuclease-free water or the manufacturer-recommended reconstitution buffer (e.g., PBS, pH 7.4)
• Bovine serum albumin (BSA) or human serum albumin (HSA) as carrier protein (0.1–1% final concentration recommended for long-term storage of reconstituted protein)
• Pyridoxal-5′-phosphate (PLP) solution (for activity assays)
• L-Alanine and α-ketoglutarate substrates (for enzymatic activity assay)
• Microcentrifuge tubes (low-binding recommended)
• Calibrated pipettes and sterile tips
• UV-Vis spectrophotometer or plate reader (340 nm capability for NADH-linked assay)
• Ice bucket and dry ice for cold-chain handling
• -20°C and/or -80°C freezer

Note: All specific buffer compositions, concentrations, and activity units should be confirmed against the product datasheet (absea#PQ-4840) prior to use.

Reconstitution and Storage Procedure

Follow these steps carefully to maintain protein integrity and enzymatic activity:

1. Equilibration: Remove the vial from -20°C or -80°C storage and allow it to equilibrate at room temperature for 10–15 minutes before opening. This minimizes condensation and protein aggregation.
2. Reconstitution: Briefly centrifuge the vial (1,000–2,000 × g, 30 seconds) to collect lyophilized material at the bottom. Add the volume of sterile reconstitution buffer specified on the product datasheet (absea#PQ-4840) directly to the lyophilized cake. Gently swirl or pipette to dissolve — do not vortex, as shear force can denature the protein.
3. Carrier Protein Addition: For long-term storage of reconstituted aliquots, supplement with BSA or HSA to a final concentration of 0.1–1% to stabilize the protein and reduce adsorption to tube surfaces.
4. Aliquoting: Divide the reconstituted protein into single-use aliquots appropriate for your experimental needs to avoid repeated freeze-thaw cycles, which degrade enzymatic activity.
5. Storage: Store aliquots at -80°C for long-term storage (up to 6–12 months recommended; verify with datasheet). Working stocks may be kept at 4°C for up to 1 week. Avoid repeated freeze-thaw cycles (limit to ≤3 cycles maximum).
6. Labeling: Label each aliquot with protein name, lot number, concentration, date of reconstitution, and initials.

Review flag: Exact reconstitution volume, buffer composition, and recommended storage duration should be verified from the official product datasheet (absea#PQ-4840) or Aladdin Scientific technical support.

Enzymatic Activity Assay Procedure

Recombinant Human GPT Protein activity is most commonly assessed using a coupled spectrophotometric assay in which pyruvate produced by GPT-catalyzed transamination is linked to NADH oxidation via lactate dehydrogenase (LDH). Monitor the decrease in absorbance at 340 nm.

Assay Principle

L-Alanine + α-Ketoglutarate ⇌ Pyruvate + L-Glutamate (catalyzed by GPT/ALT)
Pyruvate + NADH + H⁺ → L-Lactate + NAD⁺ (catalyzed by LDH, indicator reaction)

Step-by-Step Procedure

1. Prepare assay buffer: Use a suitable buffer (e.g., 100 mM Tris-HCl or phosphate buffer, pH 7.4) containing pyridoxal-5′-phosphate (PLP; typical working concentration 0.1–0.2 mM). Confirm exact buffer and PLP concentrations from the datasheet.
2. Prepare substrate mixture: Combine L-alanine (e.g., 200–500 mM), α-ketoglutarate (e.g., 5–15 mM), and NADH (e.g., 0.15–0.25 mM) with LDH (sufficient excess) in assay buffer. Specific substrate concentrations should be verified from the product datasheet.
3. Equilibrate: Warm all reagents and the spectrophotometer to 37°C (or the specified assay temperature).
4. Initiate reaction: Add a defined volume of reconstituted Recombinant Human GPT Protein to the substrate mixture to start the reaction. Mix gently.
5. Monitor absorbance: Record A340 continuously or at 30-second intervals for 5–10 minutes. Use a blank (buffer replacing enzyme) to subtract background.
6. Calculate activity: Calculate enzyme activity using the molar extinction coefficient of NADH (ε = 6,220 M⁻¹cm⁻¹ at 340 nm). Express as units/mg (U/mg) or nmol/min/mg protein.
7. Controls: Include a negative control (no enzyme) and, where possible, a positive control with a characterized GPT standard of known activity.

Review flag: Exact substrate concentrations, assay buffer, temperature, and expected specific activity values must be confirmed from the product datasheet (absea#PQ-4840). The LDH-coupled assay is standard, but verify if an alternative direct assay is recommended by the manufacturer.

Quality Control and Troubleshooting

To ensure reliable and reproducible results with Recombinant Human GPT Protein, observe the following quality control checkpoints and troubleshooting guidance:

Quality Control Checks

• Purity verification: Confirm protein purity by SDS-PAGE prior to use (expected band at the molecular weight specified on the product datasheet for GPT; theoretical MW of human GPT1 is approximately 55 kDa — verify with datasheet).
• Activity confirmation: Perform the enzymatic activity assay described above and compare measured specific activity to the value stated on the Certificate of Analysis (CoA).
• Endotoxin level: If using in cell-based assays, confirm endotoxin levels meet your experimental requirements (see CoA).

Troubleshooting Guide

Review flag: Molecular weight (~55 kDa for GPT1) is textbook-level but should be confirmed against the product datasheet (absea#PQ-4840).

Safety, Disposal, and Regulatory Notes

Safety: Recombinant Human GPT Protein is a research-use-only (RUO) reagent. It is derived from human gene sequences expressed in a recombinant system; handle in accordance with your institution's biosafety guidelines for recombinant proteins. Use standard personal protective equipment (PPE): lab coat, nitrile gloves, and safety glasses.

Biological hazard: This protein is not classified as a Select Agent. Nevertheless, good microbiological practice (GMP) should be followed. Avoid generating aerosols.

Chemical hazards: Pyridoxal-5′-phosphate (PLP) and other assay reagents should be handled according to their respective Safety Data Sheets (SDS).

Waste disposal: Dispose of protein solutions and contaminated materials according to your institution's guidelines for biological waste. Inactivation by autoclaving or chemical disinfection (e.g., 10% bleach) is acceptable prior to disposal.

Regulatory: This product is for in vitro research use only. It is not approved for use in diagnostic, therapeutic, or clinical procedures. Not for human or veterinary use.