Unique heme environment at the putative distal region of hydrogen peroxide-dependent fatty acid α-hydroxylase from Sphingomonas paucimobilis (Peroxygenase P450SPα)

Fatty acid alpha-hydroxylase from Sphingomonas paucimobilis is a hydrogen peroxide-dependent cytochrome P450 (P450) enzyme (P450(SP alpha)). In this study, heme-ligand exchange reactions of P450(SP alpha) were investigated using the optical spectroscopic method and com pared with those of various P450s, Alkylamines (C greater than or equal to 5) induced changes in the spectrum of ferric P450(SP alpha) to one typical of a nitrogenous ligand-bound low-spin form of ferric P450, although their affinities were lower than those for other P450s, and a substrate, laurate, did not interfere with the binding in contrast with in the cases of other P450s, Other compounds having a nitrogen donor atom to the heme iron of P450, including pyridine or 1-methylimidazole, induced no change in the spectrum of P450(SP alpha) in either the ferric or ferrous state. Practically no spectral change was observed on the addition of alkyl isocyanides to ferric P450s. On the other hand, cyanide induced a change in the spectrum of ferric P450(SP alpha) to one characteristic of cyanide-bound form of ferric P450, The affinity of cyanide increased when the substrate was added, in contrast with in the cases of other P450s, Ferrous P450(SP alpha) combined with CO and alkyl isocyanides, and the affinity for CO was of the same order of magnitude as in the cases of other P450s. These findings suggest a unique heme environment of P450(SP alpha) in which most compounds usually acting as external ligands of ferric P450s are prevented from gaining access to the heme iron of P450(SP alpha). The unique properties of the hydroxylase reaction catalyzed by P450(SP alpha), where an oxygen atom of hydrogen peroxide but not of molecular oxygen is utilized and incorporated into a fatty acid at its or position, is possibly related with such a specific heme environment of this P450, A possible mechanism for the peroxygenase reaction of P450(SP alpha) is proposed.