KINETICS OF THE REACTION OF 3-DEOXYHEXOSULOSE WITH THIOLS

Mercaptoethanol (ME) and glutathione (GSH) react with 3-deoxyhexosulose (DH) with 2:1 stoichiometry, the initial reaction being first order with respect to DH but zero order with respect to H+ and thiol. The reaction is accelerated by glycine and two parallel rate-determining processes, one dependent on glycine concentration, are proposed. The rate constants are compared with those for the reaction of DH with sulphite species (S(IV)), which shows similar kinetic behaviour; however, the rate constant of the DH-thiol reaction is c. 2-3 times the value of that for the DH-S(IV) reaction but the effect of glycine is smaller by a factor of c. 3. Possible differences in mechanism are considered. The reaction of DH with cysteine shows complex behaviour. An initial rapid formation of a 1:1 adduct is followed by liberation of thiol. A mechanism involving the formation of a thiazolidine compound by addition of cysteine to a carbonyl group, followed by Strecker degradation, is suggested.