Thiamine Derivatives of Disulfide Type. XII. Kinetic Studies on the Reaction between Propyl Propane-Thiolsulfinate or -Thiolsulfonate and Cysteine

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The kinetic studies were conducted on the reaction between propyl propane-thiol-sulfinate (PrSSOPr) or -thiolsulfonate (PrSSO₂Pr) and 1-cysteine. The reactions were shown by the following equations. PrSSOPr+CySH→CySSPr+(PrSOH) 2(PrSOH)→PrSSOPr+H₂O and PrSSO₂Pr+CySH→CySSPr+PrSO₂H The studies were carriepd out at an acidic pH because of the very fast rates of these reactions. The reaction species of cysteine was proved to be the protonated S-anion, RN⁺H₃·S-. The values of the enthalpy of activation and the entropy of activation were calculated to be 8.4 kcal/mole, -15.1 e.u. for PrSSOPr and 2.9 kcal/mole, -19.2 e. u. for PrSSO₂Pr.