Plasma protein-bound cysteine pool

The plasma protein-bound cysteine pool is a major extracellular reservoir of the amino acid cysteine, primarily consisting of cysteine molecules covalently linked to serum albumin via disulfide bonds (Radtke et al., 2012; Zhou et al., 2015). This pool plays a vital role in maintaining systemic thiol-disulfide redox homeostasis and serves as a buffer that regulates the availability of free cysteine in the circulation (Schmitt et al., 2015). It is a key source of cysteine for the intracellular synthesis of glutathione (GSH), the body's primary antioxidant, especially during periods of increased oxidative stress (Brummer et al., 2002). Pharmacologically, this pool is the functional target of thiol-containing drugs such as N-acetylcysteine (NAC), which displace bound cysteine through thiol-disulfide exchange reactions to increase free cysteine levels and replenish cellular GSH (ACCP, 2015). The liberated cysteine is then transported into cells, often via the cystine-glutamate antiporter (system Xc-), to support antioxidant defenses (NIH, 2012). Consequently, the modulation of this pool is a therapeutic strategy for treating conditions characterized by oxidative imbalance and glutathione depletion, including Rett syndrome, childhood adrenoleukodystrophy, and acetaminophen toxicity (NIH, 2015). The dynamics of this pool are also influenced by competing thiols like homocysteine, which can displace cysteine and contribute to vascular pathology (ResearchGate, 2005).

Other names

Protein-bound cysteineAlbumin-bound cysteineS-thiolated plasma proteinsCysteine-albumin disulfideS-cysteinylated albumin

Thiol-disulfide exchange resulting in the displacement of cysteine from protein-binding sites