Glutathione

Glutathione (L-gamma-glutamyl-L-cysteinyl-glycine, GSH) is the most abundant endogenous low-molecular-weight thiol in mammalian cells, present at 1-10 mM intracellular concentrations. It serves as the primary non-enzymatic antioxidant, as a substrate for glutathione peroxidases (GPx) and glutathione S-transferases (GST), as a cofactor for various enzymes, and as a regulator of protein function through glutathionylation of cysteine residues.

The tripeptide structure gamma-Glu-Cys-Gly contains the critical free thiol group on cysteine that provides reducing equivalents for antioxidant reactions. The gamma-glutamyl linkage (connecting glutamate's gamma-carboxylate to cysteine's amine rather than the standard alpha-carboxylate) protects glutathione from aminopeptidase degradation — a structural feature that makes glutathione substantially more stable than dipeptides with standard alpha-peptide bonds.

Research applications for Glutathione span multiple biochemical domains. Antioxidant research uses Glutathione as: DPPH and ABTS radical scavenging positive control; substrate in coupled enzyme assays measuring GPx activity (with H2O2 as substrate and NADPH consumption monitored at 340nm); standard in the DTNB colorimetric assay for total thiol measurement; and positive control for glutathione reductase (GR) activity assays measuring NADPH-dependent GSH regeneration from GSSG.

Oxidative stress research examines the GSH/GSSG ratio as an index of cellular redox state. Reduced GSH:GSSG ratios indicate oxidative stress; Glutathione supplementation in cell culture models can restore GSH pools depleted by H2O2, tert-butyl hydroperoxide, or buthionine sulfoximine (BSO, a GSH synthesis inhibitor). Comparing exogenous Glutathione with N-acetylcysteine (GSH precursor) and alpha-lipoic acid (GSSG reductase cofactor) provides mechanistic insight into which step in the GSH cycle is rate-limiting in specific oxidative stress models.

Glutathione in cell-based research: exogenous glutathione has limited cell membrane permeability under normal conditions — the charged tripeptide does not readily cross lipid bilayers by passive diffusion. For intracellular GSH supplementation in cell culture, membrane-permeable GSH precursors (N-acetylcysteine, GSH ethyl ester) or GSH monoethyl ester are typically more effective. Exogenous glutathione in cell culture medium is therefore most relevant for: studying extracellular antioxidant capacity, examining gamma-glutamyltransferase (GGT)-mediated extracellular glutathione catabolism, providing cysteine-equivalent reducing equivalents through GGT-mediated breakdown, and examining reactive oxygen species scavenging in the extracellular space.

For intracellular redox research, pair exogenous Glutathione with BSO (buthionine sulfoximine, GCL inhibitor) depletion and N-acetylcysteine supplementation to systematically manipulate the GSH biosynthesis pathway. Measure intracellular GSH/GSSG by the DTNB assay on acid-precipitated cell lysates, or use the Promega GSH/GSSG-Glo luminescent assay for high-throughput formats. For subcellular compartment-specific GSH research, use roGFP2 or Grx1-roGFP2 genetically encoded redox sensors targeted to cytoplasm, mitochondria, or ER. MW: 307.32 g/mol. CAS: 70-18-8. Store lyophilised at -20°C, desiccated, away from oxidising conditions. For laboratory and analytical research purposes only.

Oxidised glutathione (GSSG) as a research control: when studying GSH biology, GSSG (oxidised glutathione disulphide) serves as the complementary control. The GSH/GSSG ratio is the primary quantitative measure of cellular redox state — typically 100:1 or greater in healthy cells, falling to 10:1 or lower under oxidative stress. When using exogenous Glutathione in oxidative stress research, include a time-matched GSSG measurement alongside GSH to track the proportion being oxidised in the experimental system. The enzymatic cycling assay (Griffith method) measures total glutathione (GSH + 2×GSSG) and GSSG separately by masking GSH with 2-vinylpyridine, allowing GSH to be calculated by subtraction. This dual measurement provides the complete redox picture rather than total glutathione alone. For most cell-based oxidative stress research, intracellular GSH measurement by the monochlorobimane (MCB) fluorescent assay or ThiolTracker Violet dye provides real-time single-cell GSH quantification by confocal microscopy — complementing the endpoint biochemical assays. MW: 307.32 g/mol. CAS: 70-18-8. Prepare fresh, store sealed at -20°C under desiccating conditions. For laboratory and analytical research purposes only.