Start a live chat
1-800-870-4800
Glutamate, cysteine, glycine —
the three amino acids
that build glutathione.
Three amino acids, joined in a defined order, make the molecule the cell relies on. One of them — cysteine — is the amino acid the body works hardest to find. The other two are plentiful. The asymmetry between the three is, in many ways, the reason the literature on glutathione precursors exists at all.
I
Three amino acids, in a defined order —
the building blocks of the tripeptide.
Glutathione is a tripeptide — a peptide made of three amino acids. The three are glutamate (also called glutamic acid), cysteine, and glycine. They are joined in that order: glutamate first, then cysteine in the middle, then glycine at the end. The order matters. The chemistry of the molecule, and its participation in the reactions the literature describes, depends on this exact sequence. Replace any of the three amino acids and the result is no longer glutathione. Reorder them and the result is also no longer glutathione. The molecule is unambiguous.
Each of the three amino acids is naturally occurring and well-characterised. Glutamate is one of the most abundant amino acids in the human body — present in protein-rich foods, present in the body's free amino acid pool, present in nearly every cell as both a building block and a neurotransmitter. Glycine is the smallest amino acid the body uses, present in many connective tissues (including in collagen, where it occupies every third position), and abundant in the diet. Cysteine is the unusual one of the three: less abundant in food than the other two, less abundant in the body's free amino acid pool, and — alone among the three — containing a sulphur atom.
The chemistry of cysteine is what makes glutathione what it is. The sulphur atom on cysteine carries a hydrogen, forming the thiol group (-SH) that gives glutathione its working surface. The introduction to this cluster describes the thiol as the chemical reason glutathione participates in the reactions the literature describes. The reactions are sulphur chemistry. Without the cysteine, there is no sulphur. Without the sulphur, there is no glutathione as the cell uses it.
Glutamate is plentiful.
Glycine is plentiful.
Cysteine is not.
The asymmetry between the three
is the reason a literature
on glutathione precursors exists at all.
The three amino acids
Three building blocks —
each with its own biological role and its own dietary footprint.
The three amino acids that build glutathione are not interchangeable, not equivalent in cellular abundance, and not equivalent in dietary distribution. The cards below summarise the chemistry, the body's stockpile, and where each is found in the diet.
I
Glutamate
The first amino acid · plentiful
Glutamate is one of the most abundant amino acids in the body and in the diet. It functions as a major neurotransmitter, as a metabolic intermediate, and as a building block for many proteins. In glutathione, it occupies the first position — and contributes the gamma-bond that gives the molecule its unusual stability.
II
Cysteine
The middle amino acid · sulphur · rate-limiting
Cysteine carries the sulphur atom that becomes the thiol working surface of glutathione. It is conditionally essential — the body can produce it from methionine, but the pathway has limits. In free amino acid pools and in dietary supply, cysteine is consistently the least abundant of the three. The literature describes it as the rate-limiting substrate for glutathione synthesis.
III
Glycine
The third amino acid · the smallest in biology
Glycine is the smallest amino acid the body uses — a single carbon at its centre, with no side chain. It is one-third of collagen by mass and abundant in any preparation that includes connective tissue. In glutathione, it occupies the third position, and is added in the second enzymatic step of biosynthesis.
II
Why cysteine is the one —
the rate-limiting amino acid in glutathione synthesis.
The literature on glutathione synthesis has long converged on a single observation: of the three amino acids, the one that determines how much glutathione a cell can produce is almost always cysteine. The body has more glutamate than it needs for glutathione synthesis. The body has more glycine than it needs. The body, more often than not, has less free cysteine available than the synthesis machinery would otherwise use. Cysteine is the rate-limiting substrate. This observation is the conceptual anchor of an entire branch of supplementation research — the research into glutathione precursors, NAC, and the cysteine pool.
The biology of cysteine sourcing is itself complex. Cysteine is described in nutritional literature as conditionally essential — meaning it is not strictly essential (the body can produce it from methionine, another sulphur-containing amino acid) but the production pathway has limits, and dietary cysteine remains relevant. The transsulphuration pathway, by which methionine is converted to cysteine through several enzymatic steps, has been extensively studied. The pathway is itself sensitive to other nutritional cofactors, including B-vitamin status and the broader sulphur amino acid pool. Cysteine, in short, is rarely as abundant as the cell would prefer.
The sulphur atom that cysteine carries is not interchangeable with anything else. Many of the body's small molecules contain nitrogen, oxygen, carbon, hydrogen — the standard four. The sulphur amino acids (cysteine and methionine) are the principal source of biological sulphur in the body. And glutathione is one of the principal users of that sulphur. The body's sulphur economy and its glutathione economy are not the same conversation, but they are tightly linked. Anything that affects sulphur amino acid availability has implications for the cell's glutathione synthesis capacity. This is one of the reasons the field has paid such close attention to cysteine pools across decades of research.
Replace any of the three.
Reorder any of the three.
The result is no longer glutathione.
The molecule is unambiguous.
The amino acid composition
Three amino acids in defined ratios —
and one sulphur atom that does most of the chemistry.
1 : 1 : 1
The amino acid composition — one glutamate, one cysteine, one glycine per glutathione molecule
Every glutathione molecule the body produces contains exactly one of each of the three amino acids. The ratio is fixed. Whether the cell maintains glutathione at one millimolar or ten millimolar, the proportional demand for each amino acid remains the same: one for one for one.
1 of 3
Cysteine is one of just two sulphur-containing amino acids the body uses — the rare one matters
Of the twenty amino acids the body assembles into proteins, only two contain sulphur: cysteine and methionine. Both are involved in the body's sulphur economy. The presence of sulphur in cysteine is what gives glutathione its thiol working surface — and what makes cysteine availability a recurring topic in the literature.
γ-bond
The unusual gamma peptide bond between glutamate and cysteine — atypical in biology, intentional in chemistry
The bond between the first two amino acids in glutathione is a gamma-bond rather than the standard alpha-bond used in most peptide chemistry. The unusual linkage makes glutathione resistant to many of the protein-cleaving enzymes that would otherwise dismantle it. The molecule was, in effect, designed by biology to be stable.
III
Where the three amino acids appear in food —
and what dietary sourcing looks like in practice.
Glutamate is among the most widely distributed amino acids in the human diet. It is present in essentially every protein-rich food — meat, fish, eggs, dairy, legumes, grains, many vegetables. Free glutamate (not bound up in protein) is what gives many traditional culinary preparations their characteristic depth of flavour; the umami taste sensation is the taste receptor's response to free glutamate. Tomatoes, aged cheeses, fermented soy preparations, mushrooms, and slow-cooked broths all contain substantial free glutamate. The world's bone broth traditions are, in part, glutamate traditions: long simmering releases free amino acids from protein, and the broth carries them.
Glycine is similarly abundant. It is the most plentiful amino acid in collagen — by mass, approximately one-third of every collagen molecule is glycine. Any preparation that contains collagen (bone broth, gelatine, slow-cooked cuts of meat, fish skin) carries substantial glycine. Free glycine is also present in many plant proteins. Most human diets supply more than enough glycine for the body's metabolic uses, although the question of glycine adequacy under conditions of high collagen synthesis demand is a topic that has been examined in some detail in the literature.
Cysteine occupies a different place in the dietary landscape. It is present in many protein-rich foods — eggs are particularly noted, as are poultry, dairy, and some legumes — but the absolute amounts are smaller than for glutamate or glycine, and the body's metabolic uses for cysteine extend well beyond glutathione synthesis. Cysteine is needed for the production of many other sulphur-containing molecules in the body: taurine, sulphate, methionine recycling, coenzyme A, biotin metabolism, and a long list of other cellular dependents. The amount that reaches glutathione synthesis is what remains after these other demands are met. The biosynthesis pathway describes the enzymes that work with whatever cysteine the cell has available. Studies referenced were conducted independently and did not involve any specific Codeage product.
Codeage · Cellular Longevity · Pillar 03
The Codeage glutathione line —
formats from the Pillar 03 architecture.
Formulations from the Codeage glutathione line — the tripeptide the body produces, in formats designed for daily use.
Liposomal Glutathione
The flagship of the Codeage glutathione architecture. Reduced L-glutathione (GSH) supplied in a phospholipid vesicle format — the Helix Liposomal delivery system used in select Codeage formulations. The Pillar 03 anchor of the cellular redox conversation.
View Product →L-Glutathione
Reduced L-glutathione presented in a classic non-liposomal format. The molecule itself, without the vesicle architecture, for those approaching the category in its most direct form.
View Product →L-Glutathione Powder
The powder format of the direct reduced L-glutathione preparation. A simple daily approach for those building the cellular redox category into broader supplementation routines.
View Product →Article A1 · Previously in this cluster
Glutathione — The Tripeptide at the Centre of Cellular Redox Biology
Codeage · The Longevity Code
Pillar 03 —
the cellular dimension
of the longevity code.
Pillar 03 of the Longevity Code addresses the molecules the cell uses to sustain itself across time — glutathione, NMN, NAD+ precursors, and the broader cellular architecture.
Explore The Longevity Code →
