Oxygen-18 Labeling Defines a Ferric Peroxide (Compound 0) Mechanism in the Oxidative Deformylation of Aldehydes by Cytochrome P450 2B4

Abstract

Most cytochrome P450 (P450) oxidations are considered to occur with the active oxidant being a perferryl oxygen (FeO 3+ , Compound I). However, a ferric peroxide (FeO 2 ̅ , Compound 0) mechanism has been proposed, as well, particularly for aldehyde substrates. We investigated three of these systems, the oxidative deformylation of the model substrates citronellal, 2phenylpropionaldehyde, and 2-methyl-2-phenylpropionaldehyde by rabbit P450 2B4, using 18 O labeling. The formic acid product contained one 18 O derived from 18 O 2 , which is indicative of a dominant Compound 0 mechanism. The formic acid also contained only one 18 O derived from H 2 18 O, which ruled out a Compound I mechanism. The possibility of a Baeyer−Villiger reaction was examined by using synthesized possible intermediates, but our data do not support its presence. Overall, these findings unambiguously demonstrate the role of the Compound 0 pathway in these aldehyde oxidative deformylation reactions.

Local Electric Fields Drives the Proton-Coupled Electron Transfer within Cytochrome P450 Reductase

“…Cytochrome P450 monooxygenases (P450s) are prevalent in animals, plants, eukaryotes, and bacteria, catalyzing numerous essential oxidative transformations in the biosynthesis and metabolism. − In mammals, P450s are crucial for metabolizing exogenous drugs and for the biosynthesis and degradation of endogenous compounds such as hormones, fatty acids, and steroids. − The typical P450 catalytic cycle activates oxygen to form the active oxo-iron­(IV) porphyrin π-radical cation, known as Compound I (Cpd I). − Oxygen activation in this cycle typically requires two electrons, supplied by NAD­(P)H through sequential electron transfers via redox partners. , P450s are classified into two broad categories based on their redox partner systems. ,, One category uses a flavin adenine dinucleotide (FAD)-containing ferredoxin reductase (FdR) and an iron–sulfur-containing ferredoxin (Fdx), and the other uses NADPH-cytochrome P450 reductase (CPR). , CPR, the focus of this study, is the primary redox partner of microsomal cytochrome P450. − Therefore, comprehending CPR’s electron transfer mechanism is crucial for understanding drug metabolism in vivo and the pathogenesis of certain diseases.…”