The reaction of chicken liver sulfite oxidase with dimethylsulfite

Abstract

We have undertaken a steady-state and rapid kinetic study of the reaction of enzyme with sulfite and dimethylsulfite. Methylation of sulfite results in a significant increase in K m and K d for the substrate in the course of steady-state and rapid reaction kinetics, respectively, but k cat and the limiting rate constant for enzyme reduction ( k red) are essentially unchanged. This indicates that while substrate oxyanion groups are effective in stabilizing the E ox · S complex, the breakdown of this complex proceeds at the same rate even in their absence. The critical element of the substrate required for reactivity is a suitable lone-pair available to undertake nucleophilic attack on a MoO group of the active site.