Chemical mechanisms for cytochrome P-450 oxidation: spectral and catalytic properties of a manganese-substituted protein.

Abstract

Bacterial [Pseudomonas putida] cytochrome P-450 induced by camphor (P-450cam) is reconstituted with Mn protoporphyrin IX, yielding an enzyme that displays unique spectral properties relative to previously characterized Mn porphyrin systems. The nitric oxide complex of the Mn (II)-protein shows a hyper-metalloporphyrin spectrum suggestive of thiolate ligation to the porphyrin-bound Mn ion. In the presence of iodosobenzene as a source of active oxygen, Mn-substituted cytochrome P-450cam serves as a catalyst for the epoxidation of an enzyme-bound olefin substrate. This reactivity proceeds through a spectrally detectable intermediate that resembles the Mn (V)-oxo complexes; these complexes have been well documented with model systems employing artificial Mn metalloporphyrins in organic solution. Interestingly, Mn-substituted cytochrome-P-450cam shows no hydroxylation activity either in the reconstituted camphor hydroxylase system with pyridine nucleotide or in the presence of iodosobenzene and the Mn(III) form of the protein.