L-Glutathione

Research summary

L-Glutathione (GSH) is a tripeptide of glutamate, cysteine and glycine (γ-Glu-Cys-Gly) and the most abundant low-molecular-weight thiol that cells make¹. Its cysteine thiol lets it reduce oxidants and conjugate electrophiles, and the balance between reduced glutathione and its oxidized form, glutathione disulfide (GSSG), is studied as a key indicator of a cell's redox environment^1,2. Peptides Only supplies L-glutathione as a lyophilized research reagent for oxidative-stress and redox studies.

Also known as

Glutathione · GSH · Reduced glutathione · γ-L-Glutamyl-L-cysteinylglycine · Glutathion

Sequence

γ-Glu-Cys-Gly

What is L-glutathione?

Glutathione is a tripeptide with an unusual bond: its glutamate is joined to cysteine through the side-chain (γ) carboxyl group rather than the usual α-carboxyl. The reactive part of the molecule is the free thiol (–SH) of the cysteine residue.

It is the most abundant non-protein thiol in mammalian tissues, and it is built by enzymes in the cytosol rather than translated from messenger RNA: first glutamate-cysteine ligase (GCL), the rate-limiting enzyme, then glutathione synthetase. Cysteine supply and GCL activity largely set how much is made, and the genes involved are regulated by the transcription factors Nrf2, AP-1 and NF-κB³.

Glutathione and the cell's redox state

Glutathione's best-studied role is protection against oxidative damage. It reduces oxidants such as hydrogen peroxide and lipid hydroperoxides, largely as the cofactor of glutathione peroxidases, and conjugates electrophilic compounds through glutathione S-transferases^1,4. In the process, two GSH molecules are oxidized to one molecule of GSSG.

Because GSSG/2GSH is the most abundant redox couple in the cell, Schafer and Buettner proposed its half-cell reduction potential, calculated with the Nernst equation, as a quantitative measure of the cellular redox environment. In their estimates it became less negative from proliferating (about −240 mV) to differentiating (about −200 mV) to apoptotic cells (about −170 mV)².

Glutathione also acts directly on proteins. In S-glutathionylation it is attached to protein cysteine residues, a modification promoted by oxidative or nitrosative stress but also present in unstressed cells, which can regulate protein function and protect thiols from irreversible oxidation⁵. Reviews now describe glutathione as a redox-signaling molecule as well as an antioxidant, with roles studied in autophagy, nitroxidative stress and viral infection⁶.

Mitochondrial glutathione

Mitochondria are a major source of reactive oxygen species, and their glutathione pool is described as their main line of antioxidant defense⁴. Glutathione is made only in the cytosol, and how it entered mitochondria was unknown until 2021, when Wang and colleagues identified the carrier SLC25A39 as necessary for its import. Losing SLC25A39 lowered mitochondrial glutathione without changing whole-cell levels, and mitochondrial import was required for cell proliferation in culture and for red blood cell development in mice⁷.

This is where glutathione meets the mitochondrial research compounds MOTS-c and SS-31; the Thymosin Alpha-1 / L-Glutathione / MOTS-c set supplies it alongside MOTS-c.

Glutathione, GPX4 and ferroptosis

Glutathione is also central to ferroptosis, a form of non-apoptotic cell death. Screening 12 ferroptosis-inducing small molecules in cancer cell lines, Yang and colleagues found two routes to the same outcome: one class of compounds depleted glutathione, which inactivated glutathione peroxidases, while a second class inhibited the enzyme GPX4 directly. Raising or lowering GPX4 changed the lethality of all 12 ferroptosis inducers but not of 11 compounds that kill cells by other mechanisms⁸.

What human studies of oral glutathione measured

The human literature has mostly asked whether glutathione taken by mouth reaches the circulation, and the answers differ. In a 1992 study of seven healthy volunteers, plasma glutathione, cysteine and glutamate did not rise significantly over 270 minutes after a single oral administration; the authors attributed this to breakdown by γ-glutamyltransferase in the intestine and liver⁹. In a 2015 randomized, double-blind, placebo-controlled trial in 54 non-smoking adults, glutathione in whole blood, erythrocytes, plasma and lymphocytes rose over six months of daily oral intake, then returned to baseline after a one-month washout¹⁰. The two studies differ in design and duration, and their main outcomes were glutathione concentrations rather than health effects.

Working with glutathione in the lab

Because its thiol oxidizes readily, glutathione measurements depend on how samples are handled. In cultured cells, Giustarini and colleagues showed that artificial oxidation of GSH during processing inflates measured GSSG and S-glutathionylated proteins: without the thiol-blocking agent N-ethylmaleimide added immediately after removing the culture medium, basal GSSG read 3–5 times higher and S-glutathionylated proteins 10–20 times higher¹¹.

Every Peptides Only lot ships from the USA with a lot-matched certificate of analysis from an independent lab, reporting HPLC purity and mass-spec identity; certificates are published in the COA library.

Limitations of the evidence

• Most mechanistic findings, including the mitochondrial import and ferroptosis work, come from cultured cells and mice^7,8.
• Measured GSSG and GSH/GSSG ratios depend heavily on sample handling; without immediate thiol blocking, GSSG can be overestimated several-fold¹¹.
• Whole-cell glutathione does not describe the mitochondrial pool, which can fall while cellular levels stay unchanged⁷.
• Human data on oral glutathione come from few studies, with different designs and conflicting results^9,10.
• Reviews link disordered glutathione synthesis to conditions such as liver fibrosis and diabetes³; that concerns the body's own glutathione, not supplied glutathione.

Further reading

• Peptide Storage and Stability: How to Store Lyophilized Peptides