Category: amino-acid
Aliases: Cys, C, L-Cysteine
Thiol side chain forms disulfide bridges critical to protein tertiary structure (e.g., immunoglobulins, insulin, keratin). Rate-limiting precursor to glutathione (γGlu-Cys-Gly) and taurine. Central to metallothionein's metal-binding. Free cysteine is unstable in aqueous solution — most supplementation uses NAC or cystine (dimer).