Reactive sulfur species: kinetics and mechanisms of the reaction of cysteine thiosulfinate ester with cysteine to give cysteine sulfenic acid.
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.
Nagy
Péter
P
Department of Chemistry and Biochemistry, University of Oklahoma, Norman, OK 73019, USA.
Lemma
Kelemu
K
Ashby
Michael T
MT
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*
D004952:Esters; D013441:Sulfinic Acids; C100040:thiosulfinic acids; D003545:Cysteine; C013461:cysteine sulfinic acid