Is Glutathione a Peptide? γ-Bond Identity, CAS & Research Sourcing (RUO)

Yes: glutathione is a tripeptide joined by an unusual γ-peptide bond (CAS 70-18-8). Peptide Foundry identity anchors, GSH vs GSSG discipline, and reduced-GSH purity checks for research sourcing. Research use only.

Last reviewed 9 September 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 by amide bonds. Its systematic name is γ-L-glutamyl-L-cysteinyl-glycine because the glutamate–cysteine link is a γ-peptide bond formed from glutamate’s side-chain carboxyl rather than the usual α-carboxyl.

That single structural difference explains why glutathione is not made by ribosomes, why most peptidases cannot cleave it, and why registry discipline (reduced GSH versus oxidized GSSG) matters when you source research material. Peptide Foundry’s catalog lists the reduced form under CAS 70-18-8 with formula C₁₀H₁₇N₃O₆S and molar mass 307.32 g/mol.

This page keeps the γ-bond identity teaching from Peptide Foundry’s live research brief and expands research-grade sourcing: GSH versus GSSG CAS checks, the purity panels a buyer should demand, and a worked Freedom Diagnostics lot (FO498) from the gated glutathione research product page. Research use only.

Key points

• Yes — glutathione is a tripeptide: γ-L-glutamyl-L-cysteinyl-glycine (Glu–Cys–Gly).
• The Glu–Cys link is a γ-peptide bond (side-chain carboxyl), not a standard α-linkage — non-ribosomal assembly; resists most peptidases.
• PF catalog anchors: CAS 70-18-8, formula C₁₀H₁₇N₃O₆S, molar mass 307.32 g/mol, PubChem CID 124886 — reduced form (GSH).
• Current published lot on the live PDP at refresh time: FO498 (Freedom Diagnostics), 99.08% HPLC @ 214 nm, net 1458.74 mg, access Pept2608250472 — demand lot-matched COA with named lab and preferably portal verify.
• Research use only — not for human or veterinary use; not framed as a finished retail product on this research SKU.

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 (an oligopeptide, not a protein).

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. Aliases such as L-glutathione, reduced glutathione, and GSH are useful inventory shorthand. They are not identity proof. The CAS number is.

Why the γ-bond matters

Three consequences follow from the γ-linkage, all of them practical for identity literacy and sourcing 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 (also called glutamate–cysteine ligase, GCL), then glutathione synthetase. That places it in the non-ribosomal peptide class for biosynthesis literacy, even though the finished molecule looks far simpler than many microbial non-ribosomal peptides.

Most peptidases cannot cleave it

Proteolytic enzymes are shaped around the α-linkage. The γ-bond is not the usual substrate they recognise, so glutathione resists general peptidase activity. In practice one enzyme handles that bond specifically: γ-glutamyl transpeptidase. That is chemistry and pathway-class literacy — not a bioavailability or product-outcome story.

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. Parallel class-clarity reading for another tripeptide identity exemplar: GHK-Cu. For a cofactor that is often miscategorized in peptide storefronts, see NAD+.

GSH vs GSSG — CAS discipline

The cysteine residue carries a free sulfhydryl (–SH) group. That thiol is the reactive centre most analytical and handling work concerns itself with, and it is why you will see the material described two ways:

Buyer rule: if a specification does not say reduced versus oxidized, question it. Match CAS, formula, and molar mass on the certificate to the vial. Listing nicknames travel easily; registry fields do not.

Thiol handling literacy for prepared research solutions: air exposure and unnecessary freeze–thaw cycles accelerate GSH → GSSG drift. Minimise headspace and limit thaw cycles. That is laboratory handling discipline for analytical integrity — not a use schedule.

Preclinical literature discusses intracellular thiol redox, GST conjugation as a pathway class, and GSH/GSSG signaling as literature classes in redox enzymology. Those are pathway-class pointers for researchers reading primary literature. They are not product outcomes on a Peptide Foundry research SKU.

Chemical identity anchors (PF catalog)

Peptide Foundry publishes a fixed identity set for reduced glutathione. The values below match the live catalog chemistry table and the research page at refresh time. Confirm against the current product page if a lot rotates after publish.

Specification table

Naming and spelling variants

The compound appears under several labels that can all refer to reduced GSH when used carefully:

Frequent misspellings — gluthathione, glutithione, gluthione, glutathion — are common enough in catalogues and purchase orders to be worth searching when auditing inventory records. None of those variations prove what you received. CAS 70-18-8 plus formula and mass do.

What purity panels should you demand for reduced GSH?

Most suppliers publish a purity specification. A certificate of analysis is stronger when it is lot-specific, names the laboratory, states methods, and can be checked outside the supplier’s own site. For the full verification workflow — batch match, named lab, HPLC versus identity, biosafety panels, portal codes — see How to read a research-peptide COA.

Minimum research COA fields

• A lot / batch ID that matches the vial character for character
• Received / test date(s) and a named laboratory
• HPLC purity with method and wavelength (for example 214 nm)
• An identity method (MS and/or HPLC-RTM)
• Net peptide content versus labeled mass when reported

“Third-party tested” or “99%+” without a named lab and a lot number is an unfinished claim. A pretty PDF that cannot be tied to the vial in hand is documentation theater.

Full QC panels (when claimed)

When a full QC panel is present — the pattern on current Freedom Diagnostics documentation for Peptide Foundry’s glutathione listing — read these as separate analytical results:

• Heavy metals (for example ICP-MS) against stated limits
• Sterility / microbial (including PCR-based “no detectable microbial DNA” language when used)
• Endotoxin (for example USP <85>)

These describe composition and contamination panels for research documentation. They are not a safety-for-human-use claim, and they do not replace identity or purity.

Worked example — current lot FO498

As published on the current Peptide Foundry glutathione listing at the time of writing:

Historical measured-purity range published on the same product page spans 99.08%–99.836% across three lots tested by Freedom Diagnostics and Chromate. Chromate lot 35264 at 99.641% is a prior published example only — it is not the current batch. Cite the multi-lab range as Peptide Foundry–published transparency; cite FO498 as the current lot panel at refresh time. Re-verify against the live PDP if the lot rotates after publish.

Three steps that travel with any lot, not just FO498:

1. Match the lot number on the vial to the lot on the certificate.
2. Confirm CAS, formula, sequence, and reduced (GSH) language against the certificate and the product label — not GSSG.
3. Verify the access code on the issuing laboratory’s own portal when one is provided — not only by opening a PDF hosted by the supplier.

That last distinction matters. A PDF on a supplier site is a document the supplier controls. A record you can pull from the testing laboratory is not.

Research-grade sourcing checklist

Apply one checklist to every supplier, including Peptide Foundry. Category names you will see in the broader market include American Peptides, Precisely Peptides, Simple Peptide, and similar USA research-peptide vendors — treat them as a category map, not a ranking. For portable vendor criteria beyond a single SKU, see USA research-peptide vendor criteria.

Soft handoff for current lot panels and ordering: glutathione research listing (account required for the storefront; this research library stays public).

Storage and lab handling

For laboratory handling only.

• Lyophilized solid. Keep sealed and protected from light and moisture until use. Freeze-dried form is what keeps the material stable in transit relative to open aqueous prep.
• Temperature. Follow the supplier label and your institution’s SOP for cold storage of lyophilized research peptides. Brief ambient exposure in transit is normal for sealed lyophilized vials; return vials to labeled storage on arrival.
• Thiol caution. The free sulfhydryl is the fragile moiety. Air exposure converts GSH toward GSSG. Repeated freeze–thaw and prolonged open-headspace exposure both accelerate that drift. Minimise headspace and limit thaw cycles for prepared research solutions.
• Traceability. Keep the lot number with the material. Lot number ties a vial back to its certificate.

Specifics beyond lyophilized storage and thiol-oxidation awareness depend on your assay and your institution’s standard operating procedures, which take precedence over any supplier article. This page does not publish personal day-count fridge protocols, volume charts, or use schedules.

Common questions

Is glutathione a peptide or a protein?

A peptide — specifically a tripeptide (oligopeptide). Proteins are much longer polypeptide chains. Three residues with amide linkages qualifies as a peptide under the structural definition; it does not qualify as a protein.

Is glutathione the same as GSSG?

No. GSH is the reduced free-thiol form (CAS 70-18-8). GSSG is the oxidized disulfide dimer (CAS 27025-41-8). Different substances, different masses. Peptide Foundry’s PF-GLUTATHIONE listing is reduced GSH.

What CAS should match the COA?

70-18-8 for Peptide Foundry’s reduced glutathione, with formula C₁₀H₁₇N₃O₆S and molar mass 307.32 g/mol. Match those fields to the lot certificate before you accept the vial as documented.

What makes a glutathione COA usable?

Lot match to the vial, a named laboratory, HPLC purity at a stated wavelength, an identity method, and preferably net peptide content. Stronger documentation adds full QC panels and an access code you can re-check on the issuing laboratory’s portal. Worked FO498 figures and the multi-lab historical range above are examples of that pattern on Peptide Foundry’s live listing. Workflow detail: How to read a research-peptide COA.

Is this for skin, IV, or dietary-supplement use?

No. Peptide Foundry supplies glutathione strictly for laboratory and research use by qualified researchers. It is not a drug, not a dietary supplement, not a cosmetic finished good, not an infusion product, and not a veterinary product. It is not for use in people or animals. Public search queries that attach non-RUO or clinical-administration framing to “glutathione peptide” are outside the scope of this research SKU.

Next step

For the current lot certificate and product specifications, see the glutathione research product page (SKU PF-GLUTATHIONE, 1500 mg size option on the live listing). Related library reading: How to read a research-peptide COA, NAD+, GHK-Cu, and USA research-peptide vendor criteria.

Research use only. Nothing on this page describes or implies use in humans or animals.