The Journal of Biochemistry
Online ISSN : 1756-2651
Print ISSN : 0021-924X
Unique Heme Environment at the Putative Distal Region of Hydrogen Peroxide-Dependent Fatty Acid α-Hydroxylase from Sphingomonas paucinwbilis (Peroxygenase P450SPa)
Yoshio ImaiIsamu MatsunagaEmi KusunoseKosuke Ichihara
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2000 Volume 128 Issue 2 Pages 189-194

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Abstract

Fatty acid α-hydroxylase from Sphingomonas paucimobilis is a hydrogen peroxide-de-pendent cytochrome P450 (P450) enzyme (P450SPa). In this study, heme-ligand exchange reactions of P450SPa were investigated using the optical spectroscopic method and compared with those of various P450s. Alkylamines (C_??_5) induced changes in the spectrum of ferric P450SPa 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 P450SPa 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 P450SPa 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 P450SPa 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 P450SPa, in which most compounds usually acting as external ligands of ferric P450s are prevented from gaining access to the heme iron of P450SPa. The unique properties of the hydroxylase reaction catalyzed by P450SPa, where an oxygen atom of hydrogen peroxide but not of molecular oxygen is utilized and incorporated into a fatty acid at its a position, is possibly related with such a specific heme environment of this P450. A possible mechanism for the peroxygenase reaction of P450SPa is proposed.

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© The Japanese Biochemical Society
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