Structure of Cytochrome P450: Heme-Binding Site and Heme Reactivity

Abstract

Cytochrome P450 enzymes are responsible for the oxidative metabolism of a broad variety of endogenous and exogenous compounds, including sterols, fatty acids, drugs, and xenobiotics. The catalytic diversity required to bind and oxidize the many substrates of this monooxygenase system is possible due to the expression of multiple isozymes, many of which have overlapping substrate specificities. Relatively little is known about the topologies of the cytochrome P450 enzymes or the residues that control substrate specificity even though the complete sequences of over 150 cytochrome P450 isozymes have been determined. The exception to this is cytochrome P450cam, the only member of this family of enzymes for which a crystal structure is available (Poulos et al. 1987). The structure of cytochrome P450cam therefore serves as the template for all current efforts to model the active sites of cytochrome P450 enzymes.