BRS3(KC1) - Glutathione Precursor Sufficiency
(Cysteine- and glycine-linked precursor availability for glutathione synthesis)
1. Ambition
Maintain cysteine and glycine availability for glutathione synthesis so endogenous GSH-centred redox buffering can remain available under oxidative demand.
2. Core Nutritional Requirements
- Cysteine
- Glycine
3. Evidence Base
Summary
This constraint concerns cysteine and glycine availability for glutathione synthesis. Both amino acids are substrates of glutathione, and a human study in older adults with deficient synthesis found that combined provision restored synthesis and intracellular glutathione concentrations. Their availability can therefore form a coherent precursor bottleneck under relevant deficiency states. The evidence is conditional, however, and does not establish ordinary dietary limitation, a universal intake threshold or isolated effects of either amino acid in the general population (Sekhar et al., 2011).
- Constraint and membership boundary: Glutamate is required for glutathione structure but is not shown to be nutritionally limiting; polyphenols and vitamin C belong to wider redox biology rather than this precursor-availability constraint (Packer et al., 1997).
- Evidence and measurement boundary: The cited human evidence measured combined cysteine-and-glycine supplementation in older adults with deficient glutathione synthesis; it does not separate either amino acid's effect or establish the same limitation in other populations (Sekhar et al., 2011).
- Biological relevance and provision limitation: Adequate precursor availability can prevent glutathione-synthesis constraint under the studied conditions, but this does not show that extra intake improves redox function or clinical outcomes in glutathione-replete people (Sekhar et al., 2011).
Biological Importance
Cysteine is the sulfur-amino-acid substrate in glutathione. In older adults with deficient glutathione synthesis, combined cysteine and glycine provision restored synthesis, supporting conditional cysteine availability as one part of the precursor constraint.
Supporting Evidence
Sekhar et al., 2011 — Deficient glutathione synthesis in aging humans was correctable by dietary cysteine and glycine supplementation, supporting conditional precursor limitation. The trial does not establish a general-population intake threshold or isolated effects of either amino acid.
Biological Importance
Glycine contributes the terminal amino-acid residue of glutathione. In the same older-adult study, its combined provision with cysteine corrected deficient synthesis, supporting glycine as a conditional co-limiting precursor rather than a universally limiting dietary input.
Supporting Evidence
Sekhar et al., 2011 — Combined cysteine and glycine supplementation restored deficient glutathione synthesis and concentrations in older adults. The study does not isolate glycine's effect or establish ordinary dietary glycine limitation across populations.
4. Emerging Biological Supports
No Emerging Biological Supports are currently prioritised for this KC.
5. Connected Mechanisms
Functional Mechanisms
Primary Mechanisms
- BRS3-FM1-PM1 - NF-kB Signalling Regulation
- BRS3-FM2-PM3 - Nrf2-Mediated Cellular Defence Regulation
- BRS3-FM2-PM4 - ROS Generation vs Clearance Balance
- BRS3-FM2-PM5 - Lipid Peroxidation Control
- BRS3-FM1-PM2 - Gut-Derived Inflammatory Signalling
- BRS3-FM2-PM6 - Antioxidant Network Recycling
6. Key References
Core Nutritional Requirements
- Packer et al. (1997) — Vitamin E and the Metabolic Antioxidant Network
- Sekhar et al. (2011) — Deficient Synthesis of Glutathione
- Zelicha et al. (2022) — DIRECT PLUS Randomized Controlled Trial
Emerging Biological Supports
- None currently prioritised for this KC.