Mechanism of dioxygen formation catalyzed by vanadium bromoperoxidase from Macrocystis pyrifera and Fucus distichus: steady state kinetic analysis and comparison to the mechanism of V-BrPO from Ascophyllum nodosum.

Vanadium bromoperoxidase (V-BrPO) catalyzes the oxidation of bromide by hydrogen peroxide, which results in the bromation of appropriate organic substrates or the formation of dioxygen, in the absence of an organic substrate and under certain other conditions. The mechanism of the bromide-assisted disproportionation of hydrogen peroxide catalyzed by V-BrPO, which is the reaction that forms dioxygen, has been investigated for V-BrPO isolated from two new marine algal sources, Macrocystis pyrifera and Fucus distichus. The steady state kinetic studies have been performed under conditions of 0.02-40 mM H2O2, 1-500 mM Br- and pH 4.0-8.0. The rate data is consistent with a substrate-inhibited bi bi ping pong mechanism, in which the substrate bromide, is also an inhibitor by a noncompetitive-type mechanism. Bromide inhibits V-BrPO from M. pyrifera most strongly at pH 5.0-5.5 and V-BrPO from F. distichus most strongly at pH 5.5-6.0. The steady state mechanism of the Macrocystis and the Fucus enzymes are compared to the mechanism of the bromide-assisted disproportionation of hydrogen peroxide catalyzed by V-BrPO from Ascophyllum nodosum. In addition, the substrate hydrogen peroxide can also inhibit V-BrPO.