Is Glutathione a Peptide? Identity, Structure and Purity Data

Yes — glutathione is a tripeptide, but joined by an unusual γ-peptide bond that most peptides do not have. CAS 70-18-8, with third-party measured purity data.

Last reviewed 30 July 2026 · For research use only

CAS Number

70-18-8

Molecular Formula

C₁₀H₁₇N₃O₆S C10H17N3O6S

Molar Mass

307.32 g/mol

Yes. Glutathione is a tripeptide — three amino acid residues, glutamate, cysteine and glycine, joined in a single chain.

But it is an unusual one, and the reason is worth understanding if you are sourcing or characterising it: one of its two peptide bonds is a γ-linkage rather than the standard α-linkage found in essentially every ribosomally produced peptide. That single structural difference explains why glutathione is not made by ribosomes, why most peptidases cannot cleave it, and why it behaves differently from a same-length synthetic tripeptide.

Key points

• Glutathione is a tripeptide: γ-L-glutamyl-L-cysteinyl-glycine.
• Its glutamate–cysteine bond is a γ-peptide bond, formed from glutamate’s side-chain carboxyl rather than its α-carboxyl.
• Because of that bond it is not ribosomally synthesised — two ATP-dependent enzymes build it instead.
• Registered as CAS 70-18-8. Formula C₁₀H₁₇N₃O₆S, molar mass 307.32 g/mol, PubChem CID 124886.
• Current batch measured 99.641% by RP-HPLC with UV detection, independently reported.

Is glutathione a peptide, precisely?

By the standard definition — two or more amino acids joined by amide bonds between them — yes, unambiguously. Three residues makes it a tripeptide.

The complication is which carboxyl group forms the first bond.

In an ordinary peptide, residues link α-carboxyl to α-amino: the backbone carboxyl of one residue to the backbone amine of the next. Glutathione does that for its second bond (cysteine to glycine) but not its first. The glutamate–cysteine bond forms from glutamate’s side-chain carboxyl, the one on the γ-carbon.

So the full systematic name is γ-L-glutamyl-L-cysteinyl-glycine, and that leading γ is doing real work — it is not a formatting flourish.

Why the γ-bond matters

Three consequences follow from it, all of them practical rather than trivia:

It cannot be made by a ribosome

Ribosomal synthesis only forms α-peptide bonds, because it works from the amino acid backbone. Glutathione is instead assembled by two ATP-dependent enzymes — γ-glutamylcysteine synthetase, then glutathione synthetase. This makes it a non-ribosomal peptide, in the same broad class as the bacterial peptide antibiotics, despite looking far simpler than any of them.

Most peptidases cannot cleave it

Proteolytic enzymes are shaped around the α-linkage. The γ-bond is not the substrate they recognise, so glutathione resists general peptidase activity. In practice one enzyme handles that bond specifically: γ-glutamyl transpeptidase.

It is a defining example rather than an edge case

If you are building a reference set of “peptides” by structure, glutathione is the standard illustration that the category is defined by amide linkage between amino acids, not by ribosomal origin or by α-linkage alone.

What about the free thiol?

The cysteine residue carries a free sulfhydryl (–SH) group, and that is the reactive centre most analytical work concerns itself with.

It is also why you will see the material described two ways:

• GSH — reduced glutathione, the free-thiol form. This is what “glutathione” refers to unless stated otherwise.
• GSSG — oxidised glutathione, two GSH molecules joined by a disulfide bond between their cysteine thiols.

These are different substances with different CAS numbers and different masses. If a specification does not say which one it describes, that is a specification worth questioning. The material described on this page is the reduced form, GSH.

Naming and spelling variants

The compound appears under several labels, all referring to the same substance:

Frequent misspellings — gluthathione, glutithione, gluthione, glutathion — are common enough in catalogues and purchase orders to be worth searching for when auditing inventory records.

None of these variations tell you anything about what you actually received. The CAS number does.

Specification

How to verify identity independently

Do not take a supplier’s word for identity — including ours. Three checks, in order of usefulness:

1. Resolve the CAS number. 70-18-8 maps to exactly one substance. The PubChem entry gives the canonical structure, formula and mass.
2. Compare the molecular formula against the specification above. A formula mismatch is the fastest way to detect that two listings are not the same material.
3. Read the certificate, and check who issued it. A certificate is only as good as the laboratory named on it and your ability to confirm the document exists.

Measured purity

Current batch, independently reported:

The certificate for this lot can be verified directly with the issuing laboratory rather than taken from a PDF we host.

Handling and storage

For laboratory handling only.

Lyophilised material. Supplied freeze-dried, which is what keeps it stable in transit. Keep sealed and away from light and moisture until use.

Prepared samples. Store refrigerated. Prepared samples remain stable for approximately 30 days under proper refrigeration.

The thiol is the fragile part. The free sulfhydryl group oxidises on exposure to air, converting GSH to GSSG. Repeated freeze–thaw cycling and prolonged exposure to atmosphere both accelerate this. Minimise headspace, limit thaw cycles, and expect that a preparation left open will drift toward the oxidised form.

Research use only. This material is intended exclusively for in-vitro laboratory research by qualified researchers. It is not a drug, not a supplement, and not for human or veterinary use. Nothing on this page describes or implies use in humans or animals.