Chemical Identity and Physical Properties

DL-Isocitric acid trisodium salt hydrate is the trisodium salt of isocitric acid (threo-D_s-isocitric acid racemic mixture), supplied as a hydrated crystalline solid. Isocitric acid is a six-carbon tricarboxylic acid (C₆H₈O₇ in its free-acid form) bearing three carboxylate groups and one hydroxyl group. The trisodium salt form neutralises all three carboxylic acid moieties, replacing the acidic protons with sodium cations, which dramatically improves aqueous solubility compared with the free acid and facilitates precise gravimetric preparation of working solutions at physiologically relevant pH ranges.

The DL designation indicates that the material is a racemic mixture of the D- and L-enantiomers at the C-2 position (the isocitrate chiral centre acted upon by isocitrate dehydrogenase). Researchers requiring stereospecific enzymatic activity should note that only the naturally occurring threo-D_s-(−)-isocitrate enantiomer serves as the productive substrate for mammalian IDH1, IDH2, and IDH3 enzymes; nevertheless, the DL-racemate is routinely employed in assay development and calibration because of its ready commercial availability and stability.

Role in the Tricarboxylic Acid (TCA) Cycle

Isocitrate is the third intermediate of the tricarboxylic acid (Krebs) cycle. Within the cycle, citrate is first converted to isocitrate by aconitase (EC 4.2.1.3), and isocitrate is then oxidatively decarboxylated to α-ketoglutarate (2-oxoglutarate) by isocitrate dehydrogenase (IDH; EC 1.1.1.41 for NAD⁺-dependent IDH3; EC 1.1.1.42 for NADP⁺-dependent IDH1/IDH2), generating CO₂ and the reduced cofactor NADH or NADPH. This step is considered one of the key regulatory nodes of the TCA cycle.

DL-Isocitric acid trisodium salt hydrate enables researchers to supply exogenous isocitrate directly to cell-free systems, isolated mitochondria, or purified enzyme preparations without the need to generate the substrate in situ. This capability is essential for measuring IDH kinetic parameters (K_m, V_max, k_cat), studying allosteric regulation by ADP and NADH, and investigating gain-of-function IDH mutations associated with oncometabolite 2-hydroxyglutarate (2-HG) production.

Laboratory Applications

Enzyme Activity Assays: The most common application is as a direct substrate in spectrophotometric IDH activity assays. The reaction is monitored at 340 nm by tracking the increase in NADH or NADPH absorbance. The trisodium salt dissolves readily in assay buffer, enabling accurate concentration determination by weight.

Metabolic Flux Analysis: Isotopically labelled analogues aside, unlabelled DL-isocitrate trisodium salt is used to validate metabolic flux models, calibrate LC-MS/MS quantitation methods for TCA-cycle metabolite panels, and serve as an authentic reference standard for isocitrate peak identification.

Mitochondrial Function Studies: Adding exogenous isocitrate to isolated mitochondria supplements the TCA cycle substrate pool, enabling assessment of respiratory chain coupling, ATP synthesis rates, and the effect of pharmacological inhibitors on oxidative phosphorylation.

IDH Mutation Research: Cancer-associated IDH1/IDH2 neomorphic mutations (e.g., R132H, R172K) convert isocitrate to 2-HG instead of α-ketoglutarate. DL-Isocitric acid trisodium salt hydrate is used as a substrate to measure mutant IDH activity and to screen inhibitor compounds in biochemical assays.

Preparation, Handling, and Storage

Solution Preparation: Weigh the required amount under ambient conditions and dissolve in ultrapure water or the appropriate assay buffer (e.g., 50 mM Tris-HCl, pH 7.4, or 100 mM potassium phosphate, pH 7.4). Because the trisodium salt is fully ionised at physiological pH, no pH adjustment is typically required for dilute solutions; however, for concentrated stock solutions (>100 mM), verify and adjust pH as needed. Prepare fresh solutions on the day of the experiment or aliquot and store at −20 °C to minimise degradation.

Handling Precautions: Use standard laboratory personal protective equipment (lab coat, nitrile gloves, safety glasses). Avoid inhalation of dust when weighing the powder. The compound does not carry acute toxicity classifications typical of hazardous chemicals, but good laboratory practice should be observed at all times.

Storage Conditions: Store the bulk solid at 2–8 °C in a tightly sealed container protected from moisture and light. Under these conditions, the reagent is expected to retain activity for the duration of the stated shelf life. Do not store near strong oxidising agents or acids.

Quality Considerations and Purchasing Guidance

When selecting DL-Isocitric acid trisodium salt hydrate for sensitive biochemical assays, researchers should consider the following quality attributes: purity (typically ≥98% by titration or HPLC for research-grade material), identity confirmation (IR or NMR spectrum), water content (Karl Fischer titration to confirm hydration state), and heavy-metal impurity levels. Lot-specific certificates of analysis (CoA) should be requested to verify these parameters prior to use in critical experiments.

Aladdin Scientific's I106830B is supplied for research use. Researchers involved in regulated studies (e.g., IVD assay development, GMP environments) should consult with their quality assurance teams regarding suitability and additional documentation requirements. For bulk quantities or custom purity specifications, contact Aladdin Scientific's technical sales team directly.