Cytochrome P450
Cytochromes P450 (P450s or CYPs) are a superfamily of enzymes containing heme as a cofactor that mostly, but not exclusively, function as monooxygenases.[1] However, they are not omnipresent; for example, they have not been found in Escherichia coli.[2] In mammals, these enzymes oxidize steroids, fatty acids, xenobiotics, and participate in many biosyntheses.[1] By hydroxylation, CYP450 enzymes convert xenobiotics into hydrophilic derivatives, which are more readily excreted.
Further information: Cytochrome P450 (individual enzymes)P450s are, in general, the terminal oxidase enzymes in electron transfer chains, broadly categorized as P450-containing systems. The term "P450" is derived from the spectrophotometric peak at the wavelength of the absorption maximum of the enzyme (450 nm) when it is in the reduced state and complexed with carbon monoxide. Most P450s require a protein partner to deliver one or more electrons to reduce the iron (and eventually molecular oxygen).
Nomenclature[edit]
Genes encoding P450 enzymes, and the enzymes themselves, are designated with the root symbol CYP for the superfamily, followed by a number indicating the gene family, a capital letter indicating the subfamily, and another numeral for the individual gene. The convention is to italicize the name when referring to the gene. For example, CYP2E1 is the gene that encodes the enzyme CYP2E1—one of the enzymes involved in paracetamol (acetaminophen) metabolism. The CYP nomenclature is the official naming convention, although occasionally CYP450 or CYP450 is used synonymously. These names should never be used as according to the nomenclature convention (as they denote a P450 in family number 450). However, some gene or enzyme names for P450s are also referred to by historical names (e.g. P450BM3 for CYP102A1) or functional names, denoting the catalytic activity and the name of the compound used as substrate. Examples include CYP5A1, thromboxane A2 synthase, abbreviated to TBXAS1 (ThromBoXane A2 Synthase 1), and CYP51A1, lanosterol 14-α-demethylase, sometimes unofficially abbreviated to LDM according to its substrate (Lanosterol) and activity (DeMethylation).[3]
The current nomenclature guidelines suggest that members of new CYP families share at least 40% amino-acid identity, while members of subfamilies must share at least 55% amino-acid identity. Nomenclature committees assign and track both base gene names (Cytochrome P450 Homepage Archived 2010-06-27 at the Wayback Machine) and allele names (CYP Allele Nomenclature Committee).[4][5]
Related hydroxylation enzymes[edit]
Many hydroxylation reactions (insertion of hydroxyl groups) use CYP enzymes, but many other hydroxylases exist. Alpha-ketoglutarate-dependent hydroxylases also rely on an Fe=O intermediate but lack hemes. Methane monooxygenase, which converts methane to methanol, are non-heme iron-and iron-copper-based enzymes.[7]