ENZYMATIC REDUCTION OF INORGANIC ANIONS - PRE-STEADY-STATE KINETIC-ANALYSIS OF THE DISSIMILATORY SULFITE REDUCTASE (DESULFOVIRIDIN) FROM DESULFOVIBRIO-VULGARIS (HILDENBOROUGH) - MECHANISTIC IMPLICATIONS

Pre-steady-state kinetic experiments have been performed on the dissim ilatory sulfite reductase (desulfoviridin) from Desulfovibrio vulgaris (Hildenborough). Microscopic rate constants for binding (k2) and redu ctive cleavage of bonds (k(r)) during enzymatic reduction of SO32- and NO2- have been determined. For N02- reduction the reactivity of react ion intermediates has also been measured and a mechanistic scheme has been devised. The experimental rate constants are as follows: k2(SO32- ) approximately 4.3 X 10(3) M-1 s-1, kr(SO32-) approximately 12 s-1; k 2(NO2-) approximately 3.6 X 10(3) M-1 s-1, kr(NO2-) approximately 14 s -1; k2(NO) approximately 7 X 10(5) M-1 s-1, k(r)(NO) approximately 6.5 s-1, k2(NH2OH) approximately 24 M-1 s-1, kr(NH2OH) approximately 9 s- 1. Second-order rate constants for ligand association [k2(AsO2-) appro ximately 3 X 10(3) M-1 s-1; k2(HS-) approximately 1.8 M-1 s-1] are con sistent with the dominance of pi-acceptor or sigma-donor properties, r espectively, of substrate molecules. A systematic strategy for the ana lysis of a multistep enzymatic reduction of an inorganic anion is desc ribed.