title: Reactive sulfur species: kinetics and mechanisms of the reaction of cysteine thiosulfinate ester with cysteine to give cysteine sulfenic acid.
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.
authors.affiliation: Department of Chemistry and Biochemistry, University of Oklahoma, Norman, OK 73019, USA.
authors.forename: Péter
authors.initials: P
authors.lastname: Nagy
authors.forename: Kelemu
authors.initials: K
authors.lastname: Lemma
authors.forename: Michael T
authors.initials: MT
authors.lastname: Ashby
mesh_terms: D003545:Cysteine / Q000031:analogs & derivatives* / Q000138:chemical synthesis / Q000737:chemistry*; D004952:Esters / Q000737:chemistry*; D006863:Hydrogen-Ion Concentration; D007700:Kinetics; D015394:Molecular Structure; D013441:Sulfinic Acids / Q000737:chemistry*
chemical_list: D004952:Esters; D013441:Sulfinic Acids; C100040:thiosulfinic acids; D003545:Cysteine; C013461:cysteine sulfinic acid