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  • Title: Reactive sulfur species: kinetics and mechanisms of the reaction of cysteine thiosulfinate ester with cysteine to give cysteine sulfenic acid.
    Author: Nagy P, Lemma K, Ashby MT.
    Journal: J Org Chem; 2007 Nov 09; 72(23):8838-46. PubMed ID: 17941676.
    Abstract:
    The kinetics and mechanisms of the reaction of cysteine with cysteine thiosulfinate ester in aqueous solution have been studied by stopped-flow spectrophotometry between pH 6 and 14. Two reaction pathways were observed for pH > 12: (1) an essentially pH-independent nucleophilic attack of cysteinate on cysteine thiosulfinate ester, and (2) a pH-dependent fast equilibrium protonation of cysteine sulfenate that is followed by rate-limiting comproportionation of cysteine sulfenic acid with cysteinate to give cystine. For 6 < pH < 12, the rate-determining reaction between cysteinate and cysteine thiosulfinate ester becomes pH-dependent due to the protonation of their amine groups. Hydrolysis of cysteine thiosulfinate ester does not play a role in the aforementioned mechanisms because the rate-determining nucleophilic attack by hydroxide is relatively slow.
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