Functional modulation of a peroxygenase cytochrome P450: novel insight into the mechanisms of peroxygenase and peroxidase enzymes.

Cytochrome P450(BSbeta) is a peroxygenase that catalyzes the alpha- or beta-hydroxylation of myristic acid by utilizing H(2)O(2). The wild-type enzyme not only hydroxylated myristic acid, but oxidized 3,5,3',5'-tetramethylbenzidine (TMB), a peroxidase substrate, in a myristic acid-dependent reaction. Study of inhibition of hydroxylation of myristic acid by TMB indicates these two substrates compete for the same highly reactive intermediate during the course of their respective reactions. When deuterated myristic acid was used as a substrate to decrease hydroxylation activity, the rate of TMB oxidation increased. This increased rate of TMB oxidation was greatly enhanced when the R242K mutant enzyme bound with deuterated myristic acid was used. These results suggest that there are critical structural elements at the distal active site which determine whether this enzyme acts as a peroxygenase or a peroxidase.