Unique heme environment at the putative distal region of hydrogen peroxide-dependent fatty acid alpha-hydroxylase from Sphingomonas paucimobilis (Peroxygenase P450(SP alpha))

Fatty acid alpha-hydroxylase from Sphingomonas paucimobilis is a hydrogen p eroxide-dependent cytochrome P450 (P450) enzyme (P450(SP alpha)). In this s tudy, heme-ligand exchange reactions of P450(SP alpha) were investigated us ing the optical spectroscopic method and com pared with those of various P4 50s, Alkylamines (C greater than or equal to 5) induced changes in the spec trum 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 tho se for other P450s, and a substrate, laurate, did not interfere with the bi nding 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-met hylimidazole, induced no change in the spectrum of P450(SP alpha) in either the ferric or ferrous state. Practically no spectral change was observed o n the addition of alkyl isocyanides to ferric P450s. On the other hand, cya nide induced a change in the spectrum of ferric P450(SP alpha) to one chara cteristic of cyanide-bound form of ferric P450, The affinity of cyanide inc reased 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 o ther P450s. These findings suggest a unique heme environment of P450(SP alp ha) in which most compounds usually acting as external ligands of ferric P4 50s are prevented from gaining access to the heme iron of P450(SP alpha). T he 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 possibl y related with such a specific heme environment of this P450, A possible me chanism for the peroxygenase reaction of P450(SP alpha) is proposed.