Research-use information only. This page summarises published laboratory findings on glutathione. Material supplied by Peptides Lab UK is for laboratory research use only, not for human or veterinary use, and nothing here is medical or dosing advice.
Glutathione (GSH) is a tripeptide of glutamate, cysteine and glycine, and the most abundant intracellular antioxidant in mammalian cells. Its function depends almost entirely on the thiol group of its cysteine residue, which is what allows it to cycle between reduced (GSH) and oxidised (GSSG) states. The ratio between those two states is one of the most widely used measures of oxidative stress in the research literature.
What glutathione is
Glutathione is unusual among peptides in that its glutamate-cysteine bond is a gamma linkage, formed through the side-chain carboxyl rather than the standard alpha-peptide bond. That single structural detail is why glutathione resists most peptidases and can persist intracellularly at millimolar concentrations, far higher than typical signalling peptides.
It is synthesised in two ATP-dependent steps, with glutamate-cysteine ligase as the rate-limiting enzyme. Cysteine availability is generally the limiting substrate — a point that matters when interpreting studies that manipulate glutathione status indirectly.
How glutathione is described to work
- Direct radical scavenging — the cysteine thiol donates an electron, producing the oxidised dimer GSSG, which glutathione reductase recycles back to GSH using NADPH.
- Enzyme cofactor — glutathione peroxidases use GSH to reduce hydrogen peroxide and lipid peroxides.
- Phase II conjugation — glutathione S-transferases conjugate GSH to electrophilic compounds, a central mechanism in xenobiotic metabolism research.
- Protein S-glutathionylation — reversible modification of protein cysteine residues, increasingly studied as a redox signalling mechanism rather than simply as antioxidant defence.
The GSH:GSSG ratio
Most research applications are not concerned with glutathione concentration alone but with the ratio of reduced to oxidised forms. In healthy cells the literature reports this ratio as heavily weighted toward the reduced state; a fall in that ratio is a standard readout of oxidative stress.
This has a practical consequence for handling: glutathione oxidises readily on exposure to air, so sample preparation that ignores this will alter the very variable being measured.
The bioavailability problem
This is the single most important methodological point in the glutathione literature, and it is frequently glossed over. Orally administered glutathione is extensively hydrolysed to its constituent amino acids in the gut, which is why studies of oral supplementation frequently fail to show meaningful increases in tissue glutathione. Research designs that need to raise intracellular glutathione typically use precursor strategies — N-acetylcysteine being the most common — rather than administering glutathione directly.
Any study reading on glutathione status should state which route was used, because oral and parenteral routes are not comparable.
Handling, reconstitution and stability
Glutathione is supplied lyophilised and reconstituted with bacteriostatic water. Because the active thiol oxidises on air exposure, reconstituted solution has a materially shorter usable window than most research peptides, and repeated vial entry accelerates degradation. Aliquoting after reconstitution is standard practice.
Oxidised glutathione is not visually distinguishable from reduced — which is why batch-level analytical data matters here more than for stable sequences. For volume and concentration calculations use our peptide reconstitution calculator.
How glutathione differs from the peptide catalogue
Most compounds in research peptide catalogues are receptor agonists — they bind a receptor and initiate a signalling cascade. Glutathione has no receptor. It acts stoichiometrically as a redox substrate and enzyme cofactor, which means dose-response behaviour follows quite different logic from, for example, GHK-Cu or BPC-157. Protocols designed around receptor-agonist assumptions do not transfer.
There is one point of overlap worth noting: GHK-Cu research also involves copper redox chemistry, and copper and glutathione interact directly in the literature — relevant to any study running both.
The UK regulatory position
Glutathione supplied for laboratory research is not a licensed medicine in the UK and is not approved for human consumption. Injectable glutathione marketed for cosmetic skin-lightening has been the subject of regulatory warnings in multiple jurisdictions; that is a distinct use case from laboratory research supply and should not be conflated with it.
Because purity and oxidation state both affect experimental validity, insist on batch-specific analytical data. Our quality-standards SOP sets out the HPLC, mass spectrometry and endotoxin testing applied to every batch.
Frequently asked questions
What is glutathione?
A tripeptide of glutamate, cysteine and glycine, and the most abundant intracellular antioxidant in mammalian cells. Its gamma-glutamyl linkage makes it resistant to most peptidases.
How does glutathione work?
Through the thiol group on its cysteine residue, which donates electrons to neutralise reactive species. It also serves as a cofactor for glutathione peroxidases and S-transferases, and modifies protein cysteines through S-glutathionylation.
Why is oral glutathione considered poorly bioavailable?
It is extensively hydrolysed to its constituent amino acids in the gut. Studies aiming to raise intracellular glutathione typically use precursor strategies such as N-acetylcysteine instead of administering glutathione directly.
What is the GSH:GSSG ratio?
The ratio of reduced to oxidised glutathione. It is a standard research readout of oxidative stress, and a fall in the ratio indicates increased oxidative load.
How should glutathione be stored?
Lyophilised and cold. Reconstituted solution has a materially shorter usable window than most peptides because the active thiol oxidises on air exposure. Aliquot after reconstitution and minimise vial entries.
Is glutathione a peptide or an antioxidant?
Both — it is structurally a tripeptide and functionally an antioxidant. Unlike most research peptides it has no receptor and acts stoichiometrically as a redox substrate, so dose-response logic differs from receptor agonists.
Is glutathione legal in the UK?
Glutathione supplied for laboratory research is not a licensed medicine in the UK and is not approved for human consumption. Research supply, correctly labelled, is a separate lawful category from cosmetic injectable use.
Disclaimer: this content is for educational and research purposes only. Glutathione supplied by Peptides Lab UK is not intended for human or veterinary use.
