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| - Reactive Sulfur Species: Kinetics and Mechanisms of the Reactionof Cysteine Thiosulfinate Ester with Cysteine to Give CysteineSulfenic Acid
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| - The kinetics and mechanisms of the reaction of cysteine with cysteine thiosulfinate ester in aqueoussolution have been studied by stopped-flow spectrophotometry between pH 6 and 14. Two reactionpathways were observed for pH > 12: (1) an essentially pH-independent nucleophilic attack of cysteinateon cysteine thiosulfinate ester, and (2) a pH-dependent fast equilibrium protonation of cysteine sulfenatethat is followed by rate-limiting comproportionation of cysteine sulfenic acid with cysteinate to givecystine. For 6 < pH < 12, the rate-determining reaction between cysteinate and cysteine thiosulfinateester becomes pH-dependent due to the protonation of their amine groups. Hydrolysis of cysteinethiosulfinate ester does not play a role in the aforementioned mechanisms because the rate-determiningnucleophilic attack by hydroxide is relatively slow.
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