Cytochrome P450, E-class, group I, CYP2J-like (Cyt_P450_E_grp-I_CYP2J-like)
Type: Family

This entry represents the CYP2J family from group I, class E, cytochrome P450 proteins, as well as other CYP2 family proteins. The CYP2 family comprises 15 subfamilies (A-H, J-N, P and Q). The first five (A-E) are present in mammalian liver, but in differing amounts and with different inducibilities. These five subfamilies show varied substrate specificities, with some degree of overlap. Several CYP2J isoforms have been reported, including rabbit CYP2J1; human CYP2J2, the only member of the human CYP2J subfamily known for its role as arachidonic acid epoxygenase and antihistamine drugs are also substrates of it ; rat CYP2J3 and CYP2J4; mouse CYP2J5, CYP2J6, CYP2J7, CYP2J8 and CYP2J9; and rat CYP2J10. Both rat CYP2J3 and human CYP2J2 catalyse vitamin D 25-hydroxylase, but with distinct preferences: rat for vitamin D3 and human for vitamin D2 . Rat CYP2J4 is expressed in the intestine, where it is active towards all-trans and 9-cis-retinal, producing the corresponding retinoic acids . Mouse CYP2J5 is abundant in the kidney, where it is active in the metabolism of arachidonic acid to epoxyeicosatrienoic acids, and may be influenced by sex hormones .

Cytochrome P450 enzymes are a superfamily of haem-containing mono-oxygenases that are found in all kingdoms of life, and which show extraordinary diversity in their reaction chemistry. In mammals, these proteins are found primarily in microsomes of hepatocytes and other cell types, where they oxidise steroids, fatty acids and xenobiotics, and are important for the detoxification and clearance of various compounds, as well as for hormone synthesis and breakdown, cholesterol synthesis and vitamin D metabolism. In plants, these proteins are important for the biosynthesis of several compounds such as hormones, defensive compounds and fatty acids. In bacteria, they are important for several metabolic processes, such as the biosynthesis of antibiotic erythromycin in Saccharopolyspora erythraea (Streptomyces erythraeus).

Cytochrome P450 enzymes use haem to oxidise their substrates, using protons derived from NADH or NADPH to split the oxygen so a single atom can be added to a substrate. They also require electrons, which they receive from a variety of redox partners. In certain cases, cytochrome P450 can be fused to its redox partner to produce a bi-functional protein, such as with P450BM-3 from Bacillus megaterium , which has haem and flavin domains.

Organisms produce many different cytochrome P450 enzymes (at least 58 in humans), which together with alternative splicing can provide a wide array of enzymes with different substrate and tissue specificities. Individual cytochrome P450 proteins follow the nomenclature: CYP, followed by a number (family), then a letter (subfamily), and another number (protein); e.g. CYP3A4 is the fourth protein in family 3, subfamily A. In general, family members should share >40% identity, while subfamily members should share >55% identity.

Cytochrome P450 proteins can also be grouped by two different schemes. One scheme was based on a taxonomic split: class I (prokaryotic/mitochondrial) and class II (eukaryotic microsomes). The other scheme was based on the number of components in the system: class B (3-components) and class E (2-components). These classes merge to a certain degree. Most prokaryotes and mitochondria (and fungal CYP55) have 3-component systems (class I/class B) -a FAD-containing flavoprotein (NAD(P)H-dependent reductase), an iron-sulphur protein and P450. Most eukaryotic microsomes have 2-component systems (class II/class E) -NADPH:P450 reductase (FAD and FMN-containing flavoprotein) and P450. There are exceptions to this scheme, such as 1-component systems that resemble class E enzymes . The class E enzymes can be further subdivided into five sequence clusters, groups I-V, each of which may contain more than one cytochrome P450 family (eg, CYP1 and CYP2 are both found in group I). The divergence of the cytochrome P450 superfamily into B-and E-classes, and further divergence into stable clusters within the E-class, appears to be very ancient, occurring before the appearance of eukaryotes.