Mechanisms of Sulfur Transfer Catalysis

Simple thiols catalyze the transfer of a sulfur atom from thiosulfonates to cyanide by way of persulfide intermediates. Kinetic analysis of the formal mechanisms of the rhodanese-catalyzed and thiol-catalyzed transfer reactions has permitted comparative evaluation of the apparent rate constants for cleavage of the sulfur-sulfur bonds of two closely related aliphatic thiosulfonates. The results are relevant to several features of the catalytic mechanism of rhodanese. The simpler catalytic systems are inferior in protecting reactive intermediates from side reactions, as well as in overall efficiency, but appear to surpass the enzyme in formal mechanistic versatility.