The kinetics and mechanism of the oxidation of mercaptoethanol by riboflavin

Abstract

Kinetic study of the oxidation of mercaptoethanol (RSH) by riboflavin (FlH) over the pH range 8.5-10.5 establishes that the rate is given by the term 0.036[FlH][RSH][RS^-]]² mol^-2 s^-1, there being no buffer catalysis. Any reactivity of the N 3-ionized riboflavin species (Fl^-) is sufficiently low to be kinetically undetected. The kinetic form and lack of general acid catalysis are consistent with a nucleophilic (thiolate) 4a-addition-elimination mechanism previously proposed, but a possible alternative mechanism involving a flavin semiquinone (radical) intermediate is suggested.