What do glutathione S-transferases do?

They attach glutathione to electrophilic compounds, neutralising them and making them water-soluble enough to excrete.

Why are there many isoforms?

Electrophiles vary widely in shape and chemistry, so multiple active sites are needed for broad coverage.

Is glutathione recycled in this role?

No. It leaves with the conjugate and is excreted — a one-way loss, unlike its redox cycling.

Glutathione

An Enzyme Family That Uses Glutathione as a Reagent

JMWritten & reviewed by Jack Muncaster · Founder, UK PeptidesLast reviewed 2026-08-233 cited sources

Glutathione S-transferases are a family of enzymes that attach glutathione to electrophilic compounds. The conjugate is more water-soluble and can be excreted, which makes glutathione a consumed reagent in detoxification rather than a passive antioxidant.

Key facts

Enzyme family: Glutathione S-transferases (GSTs)
Reaction: Conjugation to electrophiles
Purpose: Increase water solubility for excretion
Glutathione's role: Consumed reagent, not catalyst
Review: Salinas 1999 (PMID 10101214)
Clinical example: Paracetamol metabolite conjugation

The problem these enzymes solve

Electrophilic compounds attack electron-rich sites, and cells are full of them — DNA bases, protein thiols, membrane lipids. Anything electrophilic circulating inside a cell is a hazard. It also tends to be lipophilic, which means it is difficult to excrete, so simply waiting for it to leave is not an option.

What conjugation achieves

Attaching glutathione does two things at once. It neutralises the electrophile by satisfying its reactivity with a controlled partner, and it adds a large charged group that makes the product far more water-soluble. A molecule that could not be excreted becomes one that can, and the hazard is removed in the same step.

Research material referenced

Glutathione 1500mg — third-party HPLC tested

View — £34.99

Why a whole family exists

Electrophiles vary enormously in shape and chemistry, and a single active site could not accommodate all of them. Multiple GST isoforms with different substrate preferences give broad coverage — the same solution the cytochrome P450 family represents for oxidative metabolism. Salinas reviewed the family in Current Medicinal Chemistry in 1999.

Why this makes glutathione a consumed substrate

In its redox role glutathione cycles between reduced and oxidised forms and can be regenerated. In conjugation it leaves with the compound it neutralised and is excreted. That is a one-way loss, and it is why heavy electrophile exposure depletes the pool rather than merely oxidising it.

How this connects to the paracetamol case

The reactive paracetamol metabolite is exactly the kind of electrophile this system handles, and conjugation is how it is normally cleared. Overdose overwhelms the supply rather than the enzymes, which is why the failure is depletion of the reagent rather than saturation of the catalyst.

Why antioxidant undersells the molecule

Antioxidant suggests something passively absorbing radicals. Glutathione is a substrate for at least two enzyme families — the transferases described here and the peroxidases that reduce peroxides — and a proposed carrier in amino acid transport. Its work is largely enzymatic and directed, not incidental.

Extended research context

The Glutathione deep dive

Deep dive: the bond that puts a peptide outside peptide biology

Glutamate is one of only two amino acids carrying two carboxyl groups - the backbone alpha-carboxyl every residue has, plus one on its side chain. Standard peptide bonds use the alpha. Glutathione uses the gamma, and that one choice cascades. Ribosomes have exactly one chemistry, in which an incoming residue's amine attacks the growing chain's alpha-carboxyl, and no mechanism whatsoever for recruiting a side chain. So glutathione cannot be a gene product. It is assembled instead by two ATP-dependent ligases, which means the genome encodes the machinery but never the molecule - a peptide present in nearly every cell of nearly every organism, with no coding sequence anywhere. The same geometry that excludes the ribosome also excludes most peptidases, whose active sites are built around the spacing of an alpha bond. Only gamma-glutamyl transpeptidase cleaves it, which puts turnover of a millimolar-concentration metabolite under the control of a single enzyme. Protease resistance by structural mismatch is more complete than anything proline achieves in a conventional peptide.

Deep dive: the one compound here where a purity figure does not tell you what you need

Every storage article on this site says disulfide chemistry is inapplicable, because KPV, Selank, TB-500, DSIP and Semax contain no cysteine at all. Glutathione is the compound those statements were implicitly excluding, and the exception is not marginal - its thiol is simultaneously the source of its function and its principal vulnerability. Two thiols meet, lose two hydrogens, and become GSSG at 612.6 Da. Oxygen drives it, trace metals catalyse it, no enzyme is required, and it proceeds in a vial left standing. The subtle part is that GSSG is not an impurity in the ordinary sense. It is correctly assembled glutathione in a different oxidation state, and a purity assay may well score it as related material rather than contamination. A preparation can be 99% pure and substantially oxidised at once. Where an experiment depends on the reduced form, the certificate does not answer the question - chromatography separating 307.33 from 612.6, or a thiol-specific assay, does.

Deep dive: the same question NAD+ raises, with better evidence and a less obvious answer

Both categories on this site face one structural question: does supplying the finished molecule work, or does it succeed only by being degraded to something the cell can actually use? For NAD+ the answer is fairly clearly the latter - 663 Da with two negative charges cannot cross a membrane, and CD38 degrades it outside the cell. For glutathione it is genuinely open, and the evidence is better. Richie and colleagues published a randomised controlled trial on body stores in the European Journal of Nutrition in 2015, reporting increases. But an increase in stores admits two readings: intact absorption and distribution, or degradation to glutamate, cysteine and glycine followed by resynthesis inside cells - in which case the useful contribution is essentially the cysteine, and the tripeptide is an expensive delivery vehicle for it. Since cysteine availability is what normally limits synthesis, and since gamma-glutamyl transpeptidase sits on intestinal surfaces waiting for exactly this substrate, the second reading is not a sceptical stretch. A store measurement alone cannot distinguish them.

Research applications

▸Cellular redox state measurement via GSH/GSSG ratio
▸Glutathione peroxidase and S-transferase enzyme assays
▸Oxidative stress model systems
▸Gamma-glutamyl transpeptidase activity studies
▸Thiol chemistry and disulfide exchange research
▸Melanin synthesis pathway investigation

Handling checklist

✓Verify against CID 124886, 307.33 Da, C10H17N3O6S
✓Check the oxidised form separately - GSSG is CID 65359 at 612.6 Da
✓Do not treat a purity figure as a statement about redox state
✓Store lyophilised, cold, dry; minimise headspace air
✓Prepare solutions fresh - thiol oxidation proceeds without any enzyme
✓Where the reduced form matters, assay free thiol rather than assuming

Common research-handling mistakes

Learnt from thousands of researcher orders across our UK labs.

✗ Assuming a high purity figure means the material is reduced

Fix: GSSG is correctly assembled glutathione in a different oxidation state. A purity assay may score it as related material, not contamination.

✗ Treating glutathione like the other peptides on this site

Fix: Its gamma bond makes it protease-resistant and non-ribosomal, and it is the only compound here with a reactive thiol. Most generalisations do not apply.

✗ Reading increased body stores as proof of intact absorption

Fix: Degradation to amino acids followed by intracellular resynthesis produces the same measurement. The trial endpoint cannot distinguish them.

✗ Citing the large biochemistry literature as evidence about supplementation

Fix: What glutathione does inside cells is settled. What supplementing it accomplishes is a separate and contested question.

✗ Repeating systematic review subject matter as a product claim

Fix: Describing what a literature examined and claiming a product does it are different acts. Only the first is permissible.

Continue researching

Peer-reviewed guides, comparators and matched reference materials.

Frequently asked questions

What do glutathione S-transferases do?: They attach glutathione to electrophilic compounds, neutralising them and making them water-soluble enough to excrete.
Why are there many isoforms?: Electrophiles vary widely in shape and chemistry, so multiple active sites are needed for broad coverage.
Is glutathione recycled in this role?: No. It leaves with the conjugate and is excreted — a one-way loss, unlike its redox cycling.

Primary sources & clinical trials

Peer-reviewed research and registered trials from PubMed, ClinicalTrials.gov, PubChem, FDA and NIH. All links open in a new tab and point to the primary source, so every claim can be verified at origin.

Written and reviewed by

Jack Muncaster · Founder, UK Peptides

Jack founded UK Peptides in Manchester after repeatedly receiving research compounds with missing or recycled paperwork. He is responsible for supplier selection, batch release decisions and the content published in this research library. Every article here is sourced to primary literature and every product page to a signed third-party certificate.

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