THE REACTION OF CHICKEN LIVER SULFITE OXIDASE WITH DIMETHYLSULFITE

We have undertaken a steady-state and rapid kinetic study of the react ion 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-slate 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 oxya nion groups are effective in stabilizing the E(ox) S complex, the brea kdown of this complex proceeds at the same rate even in their absence. The critical element of the substrate required for reactivity is a su itable lone-pair available to undertake nucleophilic attack on a Mo=O group of the active site.