Glutathione (GSH) is the most abundant non-protein thiol in mammalian cells. This guide covers how cells make and use it, how to read the GSH/GSSG couple, how to measure it without creating artifacts, the standard depletion and toxicology models, and how to handle the material in the lab.
Glutathione (GSH) is the tripeptide gamma-L-glutamyl-L-cysteinyl-glycine. It is the most abundant non-protein thiol in mammalian tissues, present at 1 to 10 mM, with the highest levels in liver [1]. In most cells the concentration is about 1 to 2 mM, while hepatocytes, which export glutathione, can reach about 10 mM [2]. Unlike most compounds in our catalog, glutathione is a small, well-characterized molecule with decades of literature behind it [3]. The difficult parts of working with it are rarely the biology. They are measurement, handling and interpretation, and this guide spends most of its time there.
Glutathione's glutamate is joined to cysteine through its gamma-carboxyl group rather than the usual alpha-carboxyl. That unusual bond protects it from ordinary peptidases. It is cleaved instead by gamma-glutamyl transpeptidase, an enzyme found on cell surfaces, which works with a dipeptidase to break extracellular glutathione down [2]. The cysteine thiol (-SH) does the chemical work. It donates electrons to oxidants, forms conjugates with electrophiles, and forms mixed disulfides with protein cysteines. Two oxidized glutathione molecules join as glutathione disulfide (GSSG). The research material is reduced L-glutathione, C10H17N3O6S, 307.32 Da.
Cells make glutathione in the cytosol in two ATP-dependent steps. Glutamate-cysteine ligase (GCL), made of a catalytic subunit (GCLC) and a modifier subunit (GCLM), joins glutamate and cysteine. This step is rate-limiting. Glutathione synthetase then adds glycine [1]. GSH regulates its own synthesis by feedback: it inhibits GCL competitively with glutamate, with a Ki of 2.3 mM. Cysteine supply is the other control point. The Km of GCL for cysteine is 0.1 to 0.3 mM, close to the intracellular cysteine concentration, so small changes in cysteine supply change the rate of synthesis [1]. At the gene level, GCL subunits and glutathione synthetase respond to Nrf2 acting through the antioxidant response element, as well as to AP-1 and NF-kappaB [1].
The standard tool for depleting glutathione targets the first step. Buthionine sulfoximine (BSO) inhibited gamma-glutamylcysteine synthetase (GCL) about 20 times more effectively than prothionine sulfoximine and at least 100 times more effectively than methionine sulfoximine. It did not detectably inhibit glutamine synthetase. In mice it lowered kidney glutathione to less than 20% of control levels [8]. BSO experiments remain the usual way to ask whether an outcome depends on cellular glutathione.
Glutathione protects cells from oxidants by reducing them, directly and as the substrate of glutathione peroxidases, which reduce hydrogen peroxide and lipid hydroperoxides. In the process it is oxidized to GSSG. Glutathione reductase then regenerates GSH using NADPH [2, 7]. Because the reductase depends on NADPH, a cell's glutathione capacity is also tied to its supply of NADPH.
Glutathione S-transferases attach glutathione to electrophilic compounds, including drug metabolites and products of lipid peroxidation such as 4-hydroxynonenal, which marks them for export and elimination [2]. The classic demonstration of why this matters is acetaminophen. Work in rodents published in 1973 established that hepatic glutathione protects against acetaminophen-induced liver necrosis [9]. That model is still a standard toxicology system for studying glutathione depletion.
Beyond defense, glutathione takes part in cell signaling. It influences gene expression, DNA and protein synthesis, proliferation, apoptosis and autophagy [10]. One mechanism is S-glutathionylation, in which glutathione forms a mixed disulfide with a protein cysteine and changes the protein's activity. For most proteins, spontaneous thiol-disulfide exchange with GSSG would need a GSH/GSSG ratio near 1:1, far from normal conditions [10]. In the cytosol the ratio stays very high even during oxidative stress. The endoplasmic reticulum is the exception, with a relatively high proportion of GSSG [2]. Where and how glutathionylation happens is therefore an active research question, not a simple consequence of oxidative stress.
The GSSG/2GSH couple is the most abundant redox couple in a cell, and its half-cell reduction potential can be estimated with the Nernst equation [5]. Two GSH molecules are consumed for each GSSG formed, so the potential depends on [GSH] squared over [GSSG] [1]. It is not set by the ratio alone. Two samples with the same GSH/GSSG ratio but different total glutathione have different reduction potentials, which is why it helps to report absolute concentrations alongside the ratio. Estimated potentials of the couple track cell state: about -240 mV in proliferating cells, -200 mV in differentiating cells, and -170 mV in apoptotic cells [5].
Low glutathione or a falling GSH/GSSG ratio shows up mainly as greater susceptibility to oxidative stress. That susceptibility has been linked to cancer, Parkinson's disease, Alzheimer's disease, immune function and aging. In the other direction, many tumor cells carry high glutathione levels that make them resistant to chemotherapy [4]. The same review cautions that because glutathione affects so many cellular functions, pinning down its causal role in any one disease has been difficult [4].
Most published glutathione assays descend from the enzymatic recycling method described in 1969 for nanogram amounts of total and oxidized glutathione in blood and other tissues [6]. In that method, glutathione reductase and NADPH convert GSSG to GSH, and the GSH reacts with DTNB (Ellman's reagent) to give a color change that can be measured over time [7]. The main pitfall comes before the assay. When samples are deproteinized with any of the common acids, 5 to 15% of the GSH present can oxidize to GSSG, which greatly overestimates GSSG [7]. GSSG is normally a small fraction of the total, so an artifact of a few percent of GSH can multiply the apparent GSSG several times over.
A published method avoids this by alkylating GSH with N-ethylmaleimide (NEM) before acid deproteinization, then removing excess NEM with dichloromethane. GSSG is measured by the recycling assay, and GSH is measured either by HPLC of the GS-NEM conjugate or by recycling on a separate, underivatized aliquot. The whole procedure takes 30 minutes or less [7].
Supplying glutathione from outside the cell is less direct than it sounds. Plasma glutathione is kept very low because cells break it down through surface gamma-glutamyl transpeptidase and dipeptidase, and the released cysteine then feeds glutathione synthesis in other cells [2]. In cell culture, glutathione added to the medium changes the extracellular redox environment and the supply of precursors. It cannot be assumed to raise intracellular GSH, so that should be measured rather than inferred. In a small 1992 human pharmacokinetic study, plasma glutathione did not rise significantly after a single oral load, and the authors attributed this to hydrolysis by intestinal and hepatic gamma-glutamyltransferase [11]. For studies that need to manipulate intracellular levels, the review literature discusses precursor-based approaches, and BSO provides the matching depletion arm [2, 8].
Northbridge Research Labs supplies glutathione as reduced L-glutathione, a white powder. It should be stored sealed at -20°C and is soluble in water. The thiol oxidizes in solution, so prepare solutions fresh for each experiment and check GSSG content if the redox state of the reagent matters. Keep the container closed and dry between uses. We have every batch independently tested by a third-party laboratory. The certificate for glutathione lot GT001 (1500 mg, 99.93% purity, tested August 2026) is published on our COA page.
Note: Glutathione from Northbridge Research Labs is for laboratory research use only, not for human or veterinary use. The human study mentioned above is described for its pharmacokinetic findings and is not a recommendation to consume this material.
Studied compound
Glutathione (L-Glutathione Reduced)
The same material this research covers — 99%+ purity, independently tested, with the certificate for each batch published online.
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Research Use Only: The information in this article is for educational and research purposes only. All products mentioned are intended for laboratory research use only and are not approved for human or veterinary use.