ABSTRACT
The cytochrome P450s (CYPs), a large diverse heme-containing enzyme superfamily with a large number of members, are found across all organisms in prokaryotic and eukaryotic worlds from animals, plants, fungi, protists, bacteria, and archaea to viruses (Bolwell et al. 1994; Danielson 2002; Feyereisen 1999; Gillam and Hayes 2013; Kelly and Kelly 2013; Munro and Lindsay 1996; Podust and Sherman 2012; Roberts 1999; Werck-Reichhart and Feyereisen 2000). These proteins were first discovered in 1958 by their unusual reduced carbon monoxide difference spectrum that exhibits a Soret peak at 450 nm, thus called “Pigment at 450 nm” or “P450” (Omura and Sato 1964). The unique spectral peak is produced by a thiolate anion acting as the fifth ligand to the heme. This peak is a unique feature only observed in four classes of hemoproteins, namely, P450s, nitric oxide synthases, chloroperoxidases, and protein H450 (Omura 2005; Poulos 2014; van Rantwijk and Sheldon 2000). The nomenclature of CYPs is based on the protein sequences, with similar sequences being clustered into families and subfamilies. CYP genes form a multigene family and encode proteins with amino acid sequence identities >40%. Each family comprises subfamilies with amino acid sequence identities >55%. In the classification of CYPs, a clan is defined as a higher-order category of CYP families. To date, the CYP genes from all organisms consist of at least 700 families and 800 subfamilies.
