Reference
Glutathione
**Glutathione** is a tripeptide composed of three amino acids — glutamate, cysteine, and glycine — and functions as the body's principal intracellular antioxidant. It is synthesized inside nearly every human cell, where it neutralizes reactive oxygen species and supports detoxification and protein folding.
Structure and function
Glutathione is assembled from L-glutamate, L-cysteine, and glycine through two enzyme-catalyzed steps. An unusual gamma-peptide bond links the glutamate to cysteine, which makes the molecule resistant to most ordinary peptidases and lets it persist inside cells at relatively high concentration.
Its antioxidant activity depends on the thiol (-SH) group contributed by cysteine. This sulfhydryl group donates electrons to neutralize free radicals and peroxides, after which two glutathione molecules link into an oxidized disulfide form and are later recycled back to the reduced state. The ratio between reduced and oxidized glutathione is a widely used marker of cellular oxidative status.
Why cysteine availability matters
Among the three constituent amino acids, cysteine is the rate-limiting precursor for glutathione synthesis. Glutamate and glycine are abundant in most diets, so the supply of cysteine — itself derived in part from the essential amino acid methionine — largely governs how much glutathione a cell can produce. This is why the sulfur amino acid content of a protein source is relevant to glutathione status.
Protein sources differ markedly in sulfur amino acids. Collagen is notably low in sulfur amino acids, contributing little usable cysteine. In pea protein, the sum of methionine plus cysteine is the limiting amino acid, averaging 2.6 g/100 g protein, a chemical score of 46% (Foods, 2024). A protein that supplies adequate sulfur amino acids therefore contributes more usable cysteine than one that is deficient in them.
Relevance to potato protein
Potato protein isolate is a complete protein that contributes the full set of essential amino acids, including methionine and cysteine, which makes it relevant to the dietary cysteine supply that underpins glutathione synthesis. Unlike collagen, it is not categorized as an incomplete protein, and it carries a high reported digestibility, with a DIAAS for potato protein isolates reported as high as 100 (Herreman et al., Food Science & Nutrition, 2020, PMID: 33133540). For background on the ingredient and how it is produced, see What Is Potato Protein?
Related terms