Glutathione: structure, nomenclature and handling

The three residues are glutamate, cysteine and glycine, and the sequence is conventionally written gamma-Glu-Cys-Gly. The gamma prefix is the important part. In every ordinary peptide, residues are joined between the alpha-carboxyl of one and the alpha-amino group of the next. Here the glutamate contributes its side-chain carboxyl to the bond with cysteine instead — an isopeptide linkage rather than a standard backbone one.

That single structural difference has a practical consequence: the linkage is not a substrate for the peptidases that cleave ordinary peptide bonds, which act at alpha-linkages. It also means the molecule cannot be assembled by unmodified standard peptide chemistry without deliberately directing the coupling to the side chain.

The cysteine in the middle carries a free thiol, and that group is the molecule's reactive centre. Two molecules can join through their thiols to form a disulfide-linked dimer, conventionally written GSSG, with the monomer written GSH. The two are different compounds: the monomer weighs approximately 307 daltons, the dimer approximately 613. Air alone drives the conversion, which is why the pair matters at the bench rather than only on paper.

The reduced monomer is catalogued as glutathione, reduced glutathione, GSH and L-glutathione, and carries CAS 70-18-8. The oxidized dimer is a separate catalogue entity — glutathione disulfide, oxidized glutathione or GSSG — with its own registry number and its own certificate.

Material described only as "glutathione" without the redox state named is ambiguous in a way the certificate resolves, and the two forms behave differently in essentially every assay. Both are typically supplied as free acids, sometimes as sodium salts, which affects the mass weighed out without altering identity.

High-performance liquid chromatography resolves the main peak from related substances and yields the purity figure. The characteristic related substance here is the compound's own dimer, which separates cleanly from the monomer, so a chromatogram states directly how much of a nominally reduced batch has oxidized.

Thiol-specific assay is the method that speaks to the reactive group. Ellman's reagent — 5,5'-dithiobis(2-nitrobenzoic acid) — reacts with free sulfhydryls to release a coloured product measurable by absorbance, giving a direct quantitation of thiol content that a purity assay does not provide. Where a certificate reports free thiol, that figure is the direct evidence the material is in its reduced form.

Mass spectrometry confirms the intact mass near 307 daltons and distinguishes monomer from dimer by a wide margin. The compound contains no aromatic residues, so it has essentially no absorbance at 280 nanometres; detection relies on backbone absorbance near 214 nanometres or on a thiol-specific method instead.

HEEZ Research supplies glutathione in a single format: a 1,500 mg lyophilized vial — the largest single-vial quantity in the catalogue by a wide margin.

The material is supplied as a lyophilized powder. Freeze-drying removes water and leaves the compound as a solid, markedly more stable than the same compound in solution, and stable enough at ambient temperature to ship without refrigeration in transit.

At roughly 307 daltons this is a very light molecule, so 1,500 mg represents a large molar quantity — a distinction that matters wherever protocols are specified in molar rather than mass terms.

Reconstitution converts the dried powder into a working solution, and it is a standard laboratory step rather than a product specification. Which solvent is used, and at what final concentration, is determined by the protocol in force at the receiving facility.

What HEEZ specifies is the contents of the vial: lyophilized glutathione in a single 1,500 mg format, stated on the label and on the batch certificate of analysis. Where a protocol is expressed in molar rather than mass terms, the additional figure it needs is the molecular weight, which the certificate records for the batch supplied.

Two properties of the free thiol matter once the material is wet. Dissolved oxygen drives oxidation to the dimer, and trace transition metals — copper and iron in particular — catalyse that reaction sharply, so glassware carrying metal residues from earlier procedures accelerates a change that is invisible until the material is analysed again. Alkaline conditions accelerate it further, because the deprotonated thiolate is the reactive species. Solutions of this compound are made up as needed rather than held.

Sealed lyophilized glutathione is ambient-stable for the duration of transit, so no cold chain or insulated packaging is required for shipping. On receipt the vial goes to refrigeration and is kept out of direct light.

The solid is hygroscopic, and a 1,500 mg vial will be opened repeatedly rather than used at once — so allowing a cold vial to reach room temperature before opening, and resealing promptly, matter more here than for a single-use format.

Solutions are the fragile form. Every route described above operates in aqueous media and none of them operates meaningfully in the dry solid, which is the whole reason the compound is supplied lyophilized. Repeated freeze-thaw cycling is avoided, and the practical discipline is to keep the material dry until the moment it is needed.

The certificate records what an independent facility measured for one specific batch. Its value lies in being batch-specific, so the first check is that the lot number on the document matches the vial in hand.

The identity section compares observed mass against the theoretical figure for the reduced tripeptide near 307 daltons — not the dimer near 613. Where free thiol content is reported separately, that is the figure confirming the material is in the reduced state, and it is the most informative single number on the document for this compound.

The purity figure is the HPLC main-peak area as a percentage of total peak area, and the attached chromatogram shows how that figure was arrived at. A peak corresponding to the dimer indicates oxidation rather than a synthesis fault — a different problem with a different cause, and one that gets worse with time and exposure rather than being fixed at manufacture.

Content is sometimes reported against the anhydrous free acid, accounting for residual water and counter-ions. It is the figure determining how much actual compound a nominal 1,500 mg represents, and it is meaningful for a hygroscopic solid.