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cytochrome P450
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{{Pfam box| Symbol = p450| Name = Cytochrome P450| image =Structure of lanosterol 14 α-demethylase (CYP51).png| width =| caption = Structure of lanosterol 14α-demethylase (CYP51)| Pfam= PF00067| InterPro= IPR0011| SMART=| PROSITE= PDOC00081| SCOP = 2cpp| TCDB =| OPM family= 39| OPM protein= 2bdm| PDB = | Membranome superfamily= 265}}Cytochromes P450 (CYPs) are proteins of the superfamily containing heme as a cofactor and, therefore, are hemeproteins.JOURNAL, Gonzalez FJ, Gelboin HV, Human cytochromes P450: evolution and cDNA-directed expression, Environmental Health Perspectives, 98, 81–5, November 1992, 1486867, 1519618, 10.1289/ehp.929881, CYPs use a variety of small and large molecules as substrates in enzymatic reactions. They 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.CYP enzymes have been identified in all kingdoms of life: animals, plants, fungi, protists, bacteria, archaea, and even in viruses.JOURNAL, Lamb DC, Lei L, Warrilow AG, Lepesheva GI, Mullins JG, Waterman MR, Kelly SL, The first virally encoded cytochrome p450, Journal of Virology, 83, 16, 8266–9, August 2009, 19515774, 10.1128/JVI.00289-09, 2715754, However, they are not omnipresent; for example, they have not been found in Escherichia coli.BOOK, Roland Sigel, Sigel, Astrid, Sigel, Helmut, The Ubiquitous Roles of Cytochrome P450 Proteins: Metal Ions in Life Sciences, Wiley, New York, 2007, 978-0-470-01672-5, JOURNAL, Danielson PB, The cytochrome P450 superfamily: biochemistry, evolution and drug metabolism in humans, Current Drug Metabolism, 3, 6, 561–97, December 2002, 12369887, 10.2174/1389200023337054, More than 50,000 distinct CYP proteins are known.WEB,weblink Cytochrome P450 Homepage, Nelson D, University of Tennessee, 2014-11-13, Most CYPs require a protein partner to deliver one or more electrons to reduce the iron (and eventually molecular oxygen). Based on the nature of the electron transfer proteins, CYPs can be classified into several groups:BOOK, Hanukoglu, Israel, Electron Transfer Proteins of Cytochrome P450 Systems, 14, 1996, 29–56, 1569-2558, 10.1016/S1569-2558(08)60339-2,weblink Advances in Molecular and Cell Biology, 9780762301133, The most common reaction catalyzed by cytochromes P450 is a monooxygenase reaction, e.g., insertion of one atom of oxygen into the aliphatic position of an organic substrate (RH) while the other oxygen atom is reduced to water:RH + O2 + NADPH + H+ → ROH + H2O + NADP+
Many hydroxylation reactions (insertion of hydroxyl groups) use CYP enzymes.

Nomenclature

Genes encoding CYP 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 italicise 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. However, some gene or enzyme names for CYPs may differ from this nomenclature, 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).WEB,weblink
accessdate=2007-11-19, 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. There are nomenclature committees that assign and track both base gene names (Cytochrome P450 Homepage) and allele names (CYP Allele Nomenclature Committee).

Mechanism

Image:P450cycle.svg|The P450 catalytic cycle|thumb|400px|The "Fe(V) intermediate" at the bottom left is a simplification: it is an Fe(IV) with a radical heme ligand.]]

Structure

The active site of cytochrome P450 contains a heme-iron center. The iron is tethered to the protein via a cysteine thiolate ligand. This cysteine and several flanking residues are highly conserved in known CYPs and have the formal PROSITE signature consensus pattern [FW] - [SGNH] - x - [GD] - {F} - [RKHPT] - {P} - C - [LIVMFAP] - [GAD].weblinkPROSITE consensus pattern for P450 Because of the vast variety of reactions catalyzed by CYPs, the activities and properties of the many CYPs differ in many aspects. In general, the P450 catalytic cycle proceeds as follows:

Catalytic cycle

  1. Substrate binds in proximity to the heme group, on the side opposite to the axial thiolate. Substrate binding induces a change in the conformation of the active site, often displacing a water molecule from the distal axial coordination position of the heme iron,JOURNAL, Meunier B, de Visser SP, Shaik S, Mechanism of oxidation reactions catalyzed by cytochrome p450 enzymes, Chemical Reviews, 104, 9, 3947–80, September 2004, 15352783, 10.1021/cr020443g, and changing the state of the heme iron from low-spin to high-spin.JOURNAL, Poulos TL, Finzel BC, Howard AJ, High-resolution crystal structure of cytochrome P450cam, Journal of Molecular Biology, 195, 3, 687–700, June 1987, 3656428, 10.1016/0022-2836(87)90190-2,
  2. Substrate binding induces electron transfer from NAD(P)H via cytochrome P450 reductase or another associated reductase.JOURNAL, Sligar SG, Cinti DL, Gibson GG, Schenkman JB, Spin state control of the hepatic cytochrome P450 redox potential, Biochemical and Biophysical Research Communications, 90, 3, 925–32, October 1979, 228675, 10.1016/0006-291X(79)91916-8,
  3. Molecular oxygen binds to the resulting ferrous heme center at the distal axial coordination position, initially giving a dioxygen adduct not unlike oxy-myoglobin.
  4. A second electron is transferred, from either cytochrome P450 reductase, ferredoxins, or cytochrome b5, reducing the Fe-O2 adduct to give a short-lived peroxo state.
  5. The peroxo group formed in step 4 is rapidly protonated twice, releasing one molecule of water and forming the highly reactive species referred to as P450 Compound 1 (or just Compound I). This highly reactive intermediate was isolated in 2010,JOURNAL, Rittle J, Green MT, Cytochrome P450 compound I: capture, characterization, and C-H bond activation kinetics, Science, 330, 6006, 933–7, November 2010, 21071661, 10.1126/science.1193478, 2010Sci...330..933R, P450 Compound 1 is an iron(IV) oxo (or ferryl) species with an additional oxidizing equivalent delocalized over the porphyrin and thiolate ligands. Evidence for the alternative perferryl iron(V)-oxo is lacking.
  6. Depending on the substrate and enzyme involved, P450 enzymes can catalyze any of a wide variety of reactions. A hypothetical hydroxylation is shown in this illustration. After the product has been released from the active site, the enzyme returns to its original state, with a water molecule returning to occupy the distal coordination position of the iron nucleus.
File:FeIVO 2.tif|thumb|left|300px
  1. An alternative route for mono-oxygenation is via the "peroxide shunt" (path "S" in figure). This pathway entails oxidation of the ferric-substrate complex with oxygen-atom donors such as peroxides and hypochlorites. A hypothetical peroxide "XOOH" is shown in the diagram.

Spectroscopy

Binding of substrate is reflected in the spectral properties of the enzyme, with an increase in absorbance at 390 nm and a decrease at 420 nm. This can be measured by difference spectrometry and is referred to as the "type I" difference spectrum (see inset graph in figure). Some substrates cause an opposite change in spectral properties, a "reverse type I" spectrum, by processes that are as yet unclear. Inhibitors and certain substrates that bind directly to the heme iron give rise to the type II difference spectrum, with a maximum at 430 nm and a minimum at 390 nm (see inset graph in figure). If no reducing equivalents are available, this complex may remain stable, allowing the degree of binding to be determined from absorbance measurements in vitroBOOK, Ortiz de Montellano, Paul R., Paul R. Ortiz de Montellano, Cytochrome P450: structure, mechanism, and biochemistry, 3rd, Kluwer Academic/Plenum Publishers, New York, 2005, 978-0-306-48324-0, C: If carbon monoxide (CO) binds to reduced P450, the catalytic cycle is interrupted. This reaction yields the classic CO difference spectrum with a maximum at 450 nm.

P450s in humans

Human CYPs are primarily membrane-associated proteinsJOURNAL, Berka K, Hendrychová T, Anzenbacher P, Otyepka M, Membrane position of ibuprofen agrees with suggested access path entrance to cytochrome P450 2C9 active site, The Journal of Physical Chemistry A, 115, 41, 11248–55, October 2011, 21744854, 3257864, 10.1021/jp204488j, 2011JPCA..11511248B, located either in the inner membrane of mitochondria or in the endoplasmic reticulum of cells. CYPs metabolize thousands of endogenous and exogenous chemicals. Some CYPs metabolize only one (or a very few) substrates, such as CYP19 (aromatase), while others may metabolize multiple substrates. Both of these characteristics account for their central importance in medicine. Cytochrome P450 enzymes are present in most tissues of the body, and play important roles in hormone synthesis and breakdown (including estrogen and testosterone synthesis and metabolism), cholesterol synthesis, and vitamin D metabolism. Cytochrome P450 enzymes also function to metabolize potentially toxic compounds, including drugs and products of endogenous metabolism such as bilirubin, principally in the liver.The Human Genome Project has identified 57 human genes coding for the various cytochrome P450 enzymes.WEB, P450 Table,weblink

Drug metabolism

(File:PropDrugsMetabCYP.png|thumb|400px|Proportion of antifungal drugs metabolized by different families of CYPs.doctorfungus > Antifungal Drug Interactions {{webarchive|url=https://archive.is/20120801072859weblink |date=2012-08-01 }} Content Director: Russell E. Lewis, Pharm.D. Retrieved on Jan 23, 2010){{Further|Drug metabolism}}CYPs are the major enzymes involved in drug metabolism, accounting for about 75% of the total metabolism.JOURNAL, Guengerich FP, Cytochrome p450 and chemical toxicology, Chemical Research in Toxicology, 21, 1, 70–83, January 2008, 18052394, 10.1021/tx700079z, (Metabolism in this context is the chemical modification or degradation of drugs.) Most drugs undergo deactivation by CYPs, either directly or by facilitated excretion from the body. Also, many substances are bioactivated by CYPs to form their active compounds like clopidogrel.

Drug interaction

Many drugs may increase or decrease the activity of various CYP isozymes either by inducing the biosynthesis of an isozyme (enzyme induction) or by directly inhibiting the activity of the CYP (enzyme inhibition). This is a major source of adverse drug interactions, since changes in CYP enzyme activity may affect the metabolism and clearance of various drugs. For example, if one drug inhibits the CYP-mediated metabolism of another drug, the second drug may accumulate within the body to toxic levels. Hence, these drug interactions may necessitate dosage adjustments or choosing drugs that do not interact with the CYP system. Such drug interactions are especially important to take into account when using drugs of vital importance to the patient, drugs with important side-effects and drugs with small therapeutic windows, but any drug may be subject to an altered plasma concentration due to altered drug metabolism.A classical example includes anti-epileptic drugs. Phenytoin, for example, induces CYP1A2, CYP2C9, CYP2C19, and CYP3A4. Substrates for the latter may be drugs with critical dosage, like amiodarone or carbamazepine, whose blood plasma concentration may either increase because of enzyme inhibition in the former, or decrease because of enzyme induction in the latter.{{Citation needed|date=January 2010}}

Interaction of other substances

Naturally occurring compounds may also induce or inhibit CYP activity. For example, bioactive compounds found in grapefruit juice and some other fruit juices, including bergamottin, dihydroxybergamottin, and paradicin-A, have been found to inhibit CYP3A4-mediated metabolism of certain medications, leading to increased bioavailability and, thus, the strong possibility of overdosing.JOURNAL, Bailey DG, Dresser GK, Interactions between grapefruit juice and cardiovascular drugs, American Journal of Cardiovascular Drugs, 4, 5, 281–97, 2004, 15449971, 10.2165/00129784-200404050-00002, Because of this risk, avoiding grapefruit juice and fresh grapefruits entirely while on drugs is usually advised.WEB,weblink Grapefruit juice: Can it cause drug interactions?, Zeratsky K, 2008-11-06, Ask a food & nutrition specialist, MayoClinic.com, 2009-02-09, Other examples:
  • Saint-John's wort, a common herbal remedy induces CYP3A4, but also inhibits CYP1A1, CYP1B1.JOURNAL, Chaudhary A, Willett KL, Inhibition of human cytochrome CYP 1 enzymes by flavonoids of St. John's wort, Toxicology, 217, 2–3, 194–205, January 2006, 16271822, 10.1016/j.tox.2005.09.010, JOURNAL, Strandell J, Neil A, Carlin G, An approach to the in vitro evaluation of potential for cytochrome P450 enzyme inhibition from herbals and other natural remedies, Phytomedicine, 11, 2–3, 98–104, February 2004, 15070158, 10.1078/0944-7113-00379,
  • Tobacco smoking induces CYP1A2 (example CYP1A2 substrates are clozapine, olanzapine, and fluvoxamine)JOURNAL, Kroon LA, Drug interactions with smoking, American Journal of Health-System Pharmacy, 64, 18, 1917–21, September 2007, 17823102, 10.2146/ajhp060414,
  • At relatively high concentrations, starfruit juice has also been shown to inhibit CYP2A6 and other CYPs.JOURNAL, Zhang JW, Liu Y, Cheng J, Li W, Ma H, Liu HT, Sun J, Wang LM, He YQ, Wang Y, Wang ZT, Yang L, Inhibition of human liver cytochrome P450 by star fruit juice, Journal of Pharmacy & Pharmaceutical Sciences, 10, 4, 496–503, 2007, 18261370, 10.18433/j30593, Watercress is also a known inhibitor of the cytochrome P450 CYP2E1, which may result in altered drug metabolism for individuals on certain medications (e.g., chlorzoxazone).JOURNAL, Leclercq I, Desager JP, Horsmans Y, Inhibition of chlorzoxazone metabolism, a clinical probe for CYP2E1, by a single ingestion of watercress, Clinical Pharmacology and Therapeutics, 64, 2, 144–9, August 1998, 9728894, 10.1016/S0009-9236(98)90147-3,
  • Tributyltin has been found to inhibit the function of cytochrome P450, leading to masculinization of mollusks.WEB, Walmsley, Simon, Tributyltin pollution on a global scale. An overview of relevant and recent research: impacts and issues.,weblink WWF UK,
  • Goldenseal, with its two notable alkaloids berberine and hydrastine, has been shown to alter P450-marker enzymatic activities (involving CYP2C9, CYP2D6, and CYP3A4).JOURNAL, Chatterjee P, Franklin MR, Human cytochrome p450 inhibition and metabolic-intermediate complex formation by goldenseal extract and its methylenedioxyphenyl components, Drug Metabolism and Disposition, 31, 11, 1391–7, November 2003, 14570772, 10.1124/dmd.31.11.1391,

Other specific CYP functions

Steroid hormones

File:Steroidogenesis.svg|thumb|400px|(Steroidogenesis]], showing many of the enzyme activities that are performed by cytochrome P450 enzymes.JOURNAL, Richfield, David, 2014, Diagram of the pathways of human steroidogenesis, WikiJournal of Medicine, 1, 1, 10.15347/wjm/2014.005, 2002-4436, Häggström, Mikael, HSD: Hydroxysteroid dehydrogenase.)A subset of cytochrome P450 enzymes play important roles in the synthesis of steroid hormones (steroidogenesis) by the adrenals, gonads, and peripheral tissue:

Polyunsaturated fatty acids and eicosanoids

Certain cytochrome P450 enzymes are critical in metabolizing polyunsaturated fatty acids (PUFAs) to biologically active, intercellular cell signaling molecules (eicosanoids) and/or metabolize biologically active metabolites of the PUFA to less active or inactive products. These CYPs possess cytochrome P450 omega hydroxylase and/or epoxygenase enzyme activity.
  • CYP1A1, CYP1A2, and CYP2E1 metabolize endogenous PUFAs to signaling molecules: they metabolize arachidonic acid (i.e. AA) to 19-hydroxyeicosatetraenoic acid (i.e. 19-HETE; see 20-hydroxyeicosatetraenoic acid); eicosapentaenoic acid (i.e. EPA) to epoxyeicosatetraenoic acids (i.e. EEQs); and docosahexaenoic acid (i.e. DHA) to epoxydocosapentaenoic acids (i.e. EDPs).
  • CYP2C8, CYP2C9, CYP2C18, CYP2C19, and CYP2J2 metabolize endogenous PUFAs to signaling molecules: they metabolize AA to epoxyeicosatetraenoic acids (i.e. EETs); EPA to EEQs; and DHA to EDPs.
  • CYP2S1 metabolizes PUFA to signaling molecules: it metabolizes AA to EETs ad EPA to EEQs.
  • CYP3A4 metabolizes AA to EET signaling molecules.
  • CYP4A11 metabolizes endogenous PUFAs to signaling molecules: it metabolizes AA to 20-HETE and EETs; it also hydroxylates DHA to 22-hydroxy-DHA (i.e. 12-HDHA).
  • CYP4F2, CYP4F3A, and CYP4F3B (see CYP4F3 for latter two CYPs) metabolize PUFAs to signaling molecules: they metabolizes AA to 20-HETE. They also metabolize EPA to 19-hydroxyeicosapentaenoic acid (19-HEPE) and 20-hydroxyeicosapentaenoic acid (20-HEPE) as well as metabolize DHA to 22-HDA. They also inactivate or reduce the activity of signaling molecules: they metabolize leukotriene B4 (LTB4) to 20-hydroxy-LTB4, 5-hydroxyeicosatetraenoic acid (5-HETE) to 5,20-diHETE, 5-oxo-eicosatetraenoic acid (5-oxo-ETE) to 5-oxo,20-hydroxy-ETE, 12-hydroxyeicosatetraenoic acid (12-HETE) to 12,20-diHETE, EETs to 20-hydroxy-EETs, and lipoxins to 20-hydroxy products.
  • CYP4F8 and CYP4F12 metabolize PUFAs to signaling molecules: they metabolizes EPA to EEQs and DHA to EDPs. They also metabolize AA to 18-hydroxyeicosatetraenoic acid (18-HETE) and 19-HETE.
  • CYP4F11 inactivates or reduces the activity of signaling molecules: it metabolizes LTB4 to 20-hydroxy-LTB4, (5-HETE) to 5,20-diHETE, (5-oxo-ETE) to 5-oxo,20-hydroxy-ETE, (12-HETE) to 12,20-diHETE, EETs to 20-hydroxy-EETs, and lipoxins to 20-hydroxy products.
  • CYP4F22 ω-hydroxylates extremely long "very long chain fatty acids", i.e. fatty acids that are 28 or more carbons long. The ω-hydroxylation of these special fatty acids is critical to creating and maintaining the skins water barrier function; autosomal recessive inactivating mutations of CYP4F22 are associated with the Lamellar ichthyosis subtype of Congenital ichthyosiform erythrodema in humans.JOURNAL, Sugiura K, Akiyama M, Update on autosomal recessive congenital ichthyosis: mRNA analysis using hair samples is a powerful tool for genetic diagnosis, Journal of Dermatological Science, 79, 1, 4–9, July 2015, 25982146, 10.1016/j.jdermsci.2015.04.009,

CYP families in humans

Humans have 57 genes and more than 59 pseudogenes divided among 18 families of cytochrome P450 genes and 43 subfamilies.Nelson D (2003). Cytochromes P450 in humans. Retrieved May 9, 2005. This is a summary of the genes and of the proteins they encode. See the homepage of the cytochrome P450 Nomenclature Committee for detailed information.{| class="wikitable"
Family >Function >Members >| Names
|-
| CYP1 || drug and steroid (especially estrogen) metabolism, benzo[a]pyrene toxification (forming (+)-benzo[a]pyrene-7,8-dihydrodiol-9,10-epoxide) || 3 subfamilies, 3 genes, 1 pseudogene || CYP1A1, CYP1A2, CYP1B1
|-
| CYP2 || drug and steroid metabolism || 13 subfamilies, 16 genes, 16 pseudogenes || CYP2A6, CYP2A7, CYP2A13, CYP2B6, CYP2C8, CYP2C9, CYP2C18, CYP2C19, CYP2D6, CYP2E1, CYP2F1, CYP2J2, CYP2R1, CYP2S1, CYP2U1, CYP2W1
|-
| CYP3 || drug and steroid (including testosterone) metabolism || 1 subfamily, 4 genes, 2 pseudogenes || CYP3A4, CYP3A5, CYP3A7, CYP3A43
|-
| CYP4 || arachidonic acid or fatty acid metabolism || 6 subfamilies, 12 genes, 10 pseudogenes || CYP4A11, CYP4A22, CYP4B1, CYP4F2, CYP4F3, CYP4F8, CYP4F11, CYP4F12, CYP4F22, CYP4V2, CYP4X1, CYP4Z1
|-
| CYP5 || thromboxane A2 synthase || 1 subfamily, 1 gene || CYP5A1
|-
| CYP7 || bile acid biosynthesis 7-alpha hydroxylase of steroid nucleus || 2 subfamilies, 2 genes || CYP7A1, CYP7B1
|-
| CYP8 || varied || 2 subfamilies, 2 genes || CYP8A1 (prostacyclin synthase), CYP8B1 (bile acid biosynthesis)
|-
| CYP11 || steroid biosynthesis || 2 subfamilies, 3 genes || CYP11A1, CYP11B1, CYP11B2
|-
| CYP17 || steroid biosynthesis, 17-alpha hydroxylase || 1 subfamily, 1 gene || CYP17A1
|-
| CYP19 || steroid biosynthesis: aromatase synthesizes estrogen || 1 subfamily, 1 gene || CYP19A1
|-
| CYP20 || unknown function || 1 subfamily, 1 gene || CYP20A1
|-
| CYP21 || steroid biosynthesis || 2 subfamilies, 1 gene, 1 pseudogene || CYP21A2
|-
| CYP24 || vitamin D degradation || 1 subfamily, 1 gene || CYP24A1
|-
| CYP26 || retinoic acid hydroxylase || 3 subfamilies, 3 genes || CYP26A1, CYP26B1, CYP26C1
|-
| CYP27 || varied || 3 subfamilies, 3 genes || CYP27A1 (bile acid biosynthesis), CYP27B1 (vitamin D3 1-alpha hydroxylase, activates vitamin D3), CYP27C1 (unknown function)
|-
| CYP39 || 7-alpha hydroxylation of 24-hydroxycholesterol || 1 subfamily, 1 gene || CYP39A1
|-
| CYP46 || cholesterol 24-hydroxylase || 1 subfamily, 1 gene || CYP46A1
|-
| CYP51 || cholesterol biosynthesis || 1 subfamily, 1 gene, 3 pseudogenes || CYP51A1 (lanosterol 14-alpha demethylase)

P450s in other species

Animals

Many animals have as many or more CYP genes than humans do. Reported numbers range from 35 genes in the sponge Amphimedon queenslandica to 235 genes in the cephalochordate Branchiostoma floridae.JOURNAL, Nelson DR, Goldstone JV, Stegeman JJ, The cytochrome P450 genesis locus: the origin and evolution of animal cytochrome P450s, Philosophical Transactions of the Royal Society of London. Series B, Biological Sciences, 368, 1612, 20120474, February 2013, 23297357, 3538424, 10.1098/rstb.2012.0474, Mice have genes for 101 CYPs, and sea urchins have even more (perhaps as many as 120 genes).JOURNAL, Goldstone JV, Hamdoun A, Cole BJ, Howard-Ashby M, Nebert DW, Scally M, Dean M, Epel D, Hahn ME, Stegeman JJ, The chemical defensome: environmental sensing and response genes in the Strongylocentrotus purpuratus genome, Developmental Biology, 300, 1, 366–84, December 2006, 17097629, 3166225, 10.1016/j.ydbio.2006.08.066, Most CYP enzymes are presumed to have monooxygenase activity, as is the case for most mammalian CYPs that have been investigated (except for, e.g., CYP19 and CYP5). Gene and genome sequencing is far outpacing biochemical characterization of enzymatic function, though many genes with close homology to CYPs with known function have been found, giving clues to their functionality.The classes of CYPs most often investigated in non-human animals are those either involved in development (e.g., retinoic acid or hormone metabolism) or involved in the metabolism of toxic compounds (such as heterocyclic amines or polyaromatic hydrocarbons). Often there are differences in gene regulation or enzyme function of CYPs in related animals that explain observed differences in susceptibility to toxic compounds (ex. canines inability to metabolize xanthines such as caffeine). Some drugs undergo metabolism in both species via different enzymes, resulting in different metabolites, while other drugs are metabolized in one species but excreted unchanged in another species. For this reason, one species's reaction to a substance is not a reliable indication of the substance's effects in humans.CYPs have been extensively examined in mice, rats, dogs, and less so in zebrafish, in order to facilitate use of these model organisms in drug discovery and toxicology. Recently CYPs have also been discovered in avian species, in particular turkeys, that may turn out to be a useful model for cancer research in humans.JOURNAL, Rawal S, Kim JE, Coulombe R, Aflatoxin B1 in poultry: toxicology, metabolism and prevention, Research in Veterinary Science, 89, 3, 325–31, December 2010, 20462619, 10.1016/j.rvsc.2010.04.011, CYP1A5 and CYP3A37 in turkeys were found to be very similar to the human CYP1A2 and CYP3A4 respectively, in terms of their kinetic properties as well as in the metabolism of aflatoxin B1.JOURNAL, Rawal S, Coulombe RA, Metabolism of aflatoxin B1 in turkey liver microsomes: the relative roles of cytochromes P450 1A5 and 3A37, Toxicology and Applied Pharmacology, 254, 3, 349–54, August 2011, 21616088, 10.1016/j.taap.2011.05.010, CYPs have also been heavily studied in insects, often to understand pesticide resistance. For example, CYP6G1 is linked to insecticide resistance in DDT-resistant Drosophila melanogasterJOURNAL, McCart C, Ffrench-Constant RH, Dissecting the insecticide-resistance- associated cytochrome P450 gene Cyp6g1, Pest Management Science, 64, 6, 639–45, June 2008, 18338338, 10.1002/ps.1567, and CYP6Z1 in the mosquito malaria vector Anopheles gambiae is capable of directly metabolizing DDT.JOURNAL, Chiu TL, Wen Z, Rupasinghe SG, Schuler MA, Comparative molecular modeling of Anopheles gambiae CYP6Z1, a mosquito P450 capable of metabolizing DDT, Proceedings of the National Academy of Sciences of the United States of America, 105, 26, 8855–60, July 2008, 18577597, 2449330, 10.1073/pnas.0709249105, 2008PNAS..105.8855C,

Microbial

Microbial cytochromes P450 are often soluble enzymes and are involved in diverse metabolic processes. In bacteria the distribution of P450s is very variable with many bacteria having no identified P450s (e.g. E.coli). Some bacteria, predominantly actinomycetes, have numerous P450s (e.g.,JOURNAL, McLean KJ, Clift D, Lewis DG, Sabri M, Balding PR, Sutcliffe MJ, Leys D, Munro AW, The preponderance of P450s in the Mycobacterium tuberculosis genome, Trends in Microbiology, 14, 5, 220–8, May 2006, 16581251, 10.1016/j.tim.2006.03.002, JOURNAL, Ikeda H, Ishikawa J, Hanamoto A, Shinose M, Kikuchi H, Shiba T, Sakaki Y, Hattori M, Omura S, Complete genome sequence and comparative analysis of the industrial microorganism Streptomyces avermitilis, Nature Biotechnology, 21, 5, 526–31, May 2003, 12692562, 10.1038/nbt820, ). Those so far identified are generally involved in either biotransformation of xenobiotic compounds (e.g. CYP105A1 from Streptomyces griseolus metabolizes sulfonylurea herbicides to less toxic derivatives,JOURNAL, Leto, O'Keefe, Identification of constitutive and herbicide inducible cytochromes P-450 in Streptomyces griseolus, Arch Microbiol, 1988, 149, 5, 406–12, 10.1007/BF00425579, ) or are part of specialised metabolite biosynthetic pathways (e.g. CYP170B1 catalyses production of the sesquiterpenoid albaflavenone in Streptomyces albus,JOURNAL, Moody SC, Zhao B, Lei L, Nelson DR, Mullins JG, Waterman MR, Kelly SL, Lamb DC, Investigating conservation of the albaflavenone biosynthetic pathway and CYP170 bifunctionality in streptomycetes, The FEBS Journal, 279, 9, 1640–9, May 2012, 22151149, 10.1111/j.1742-4658.2011.08447.x, ). Although no P450 has yet been shown to be essential in a microbe, the CYP105 family is highly conserved with a representative in every streptomycete genome sequenced so far (JOURNAL, Moody SC, Loveridge EJ, CYP105-diverse structures, functions and roles in an intriguing family of enzymes in Streptomyces, Journal of Applied Microbiology, 117, 6, 1549–63, December 2014, 25294646, 4265290, 10.1111/jam.12662, ). Due to the solubility of bacterial P450 enzymes, they are generally regarded as easier to work with than the predominantly membrane bound eukaryotic P450s. This, combined with the remarkable chemistry they catalyse, has led to many studies using the heterologously expressed proteins in vitro. Few studies have investigated what P450s do in vivo, what the natural substrate(s) are and how P450s contribute to survival of the bacteria in the natural environment.Three examples that have contributed significantly to structural and mechanistic studies are listed here, but many different families exist.
  • Cytochrome P450cam (CYP101) originally from Pseudomonas putida has been used as a model for many cytochromes P450 and was the first cytochrome P450 three-dimensional protein structure solved by X-ray crystallography. This enzyme is part of a camphor-hydroxylating catalytic cycle consisting of two electron transfer steps from putidaredoxin, a 2Fe-2S cluster-containing protein cofactor.
  • Cytochrome P450 eryF (CYP107A1) originally from the actinomycete bacterium Saccharopolyspora erythraea is responsible for the biosynthesis of the antibiotic erythromycin by C6-hydroxylation of the macrolide 6-deoxyerythronolide B.
  • Cytochrome P450 BM3 (CYP102A1) from the soil bacterium Bacillus megaterium catalyzes the NADPH-dependent hydroxylation of several long-chain fatty acids at the ω–1 through ω–3 positions. Unlike almost every other known CYP (except CYP505A1, cytochrome P450 foxy), it constitutes a natural fusion protein between the CYP domain and an electron donating cofactor. Thus, BM3 is potentially very useful in biotechnological applications.JOURNAL, Narhi LO, Fulco AJ, Characterization of a catalytically self-sufficient 119,000-dalton cytochrome P-450 monooxygenase induced by barbiturates in Bacillus megaterium, The Journal of Biological Chemistry, 261, 16, 7160–9, June 1986, 3086309,weblink JOURNAL, Girvan HM, Waltham TN, Neeli R, Collins HF, McLean KJ, Scrutton NS, Leys D, Munro AW, Flavocytochrome P450 BM3 and the origin of CYP102 fusion species, Biochemical Society Transactions, 34, Pt 6, 1173–7, December 2006, 17073779, 10.1042/BST0341173,
  • Cytochrome P450 119 (CYP119) isolated from the thermophillic archea Sulfolobus acidocaldarius JOURNAL, Wright RL, Harris K, Solow B, White RH, Kennelly PJ, Cloning of a potential cytochrome P450 from the archaeon Sulfolobus solfataricus, FEBS Letters, 384, 3, 235–9, April 1996, 8617361, 10.1016/0014-5793(96)00322-5, has been used in a variety of mechanistic studies. Because thermophillic enzymes evolved to function at high temperatures, they tend to function more slowly at room temperature (if at all) and are therefore excellent mechanistic models.

Fungi

The commonly used azole class antifungal drugs work by inhibition of the fungal cytochrome P450 14α-demethylase. This interrupts the conversion of lanosterol to ergosterol, a component of the fungal cell membrane. (This is useful only because humans' P450 have a different sensitivity; this is how this class of antifungals work.)JOURNAL, Vanden Bossche H, Marichal P, Gorrens J, Coene MC, Biochemical basis for the activity and selectivity of oral antifungal drugs, British Journal of Clinical Practice. Supplement, 71, 41–6, September 1990, 2091733, Significant research is ongoing into fungal P450s, as a number of fungi are pathogenic to humans (such as Candida yeast and Aspergillus) and to plants.Cunninghamella elegans is a candidate for use as a model for mammalian drug metabolism.

Plants

Plant cytochrome P450s are involved in a wide range of biosynthetic reactions and target a diverse range of biomolecules. These reactions lead to various fatty acid conjugates, plant hormones, secondary metabolites, lignins, and a variety of defensive compounds.JOURNAL, Schuler MA, Werck-Reichhart D, Functional genomics of P450s, Annual Review of Plant Biology, 54, 1, 629–67, 2003-01-01, 14503006, 10.1146/annurev.arplant.54.031902.134840, Plant genome annotations suggest that cytochrome P450 genes make up as much as 1% of the plant genes. The number and diversity of P450 genes is responsible, in part, for the multitude of bioactive compounds.JOURNAL, Mizutani M, Sato F, Unusual P450 reactions in plant secondary metabolism, Archives of Biochemistry and Biophysics, 507, 1, 194–203, March 2011, 20920462, 10.1016/j.abb.2010.09.026,weblink P450 Catalysis Mechanisms,

P450s in biotechnology

The remarkable reactivity and substrate promiscuity of P450s have long attracted the attention of chemists.JOURNAL, Chefson A, Auclair K, Progress towards the easier use of P450 enzymes, Molecular BioSystems, 2, 10, 462–9, October 2006, 17216026, 10.1039/b607001a, Recent progress towards realizing the potential of using P450s towards difficult oxidations have included: (i) eliminating the need for natural co-factors by replacing them with inexpensive peroxide containing molecules,JOURNAL, Chefson A, Zhao J, Auclair K, Replacement of natural cofactors by selected hydrogen peroxide donors or organic peroxides results in improved activity for CYP3A4 and CYP2D6, ChemBioChem, 7, 6, 916–9, June 2006, 16671126, 10.1002/cbic.200600006, (ii) exploring the compatibility of P450s with organic solvents,JOURNAL, Chefson A, Auclair K, CYP3A4 activity in the presence of organic cosolvents, ionic liquids, or water-immiscible organic solvents, ChemBioChem, 8, 10, 1189–97, July 2007, 17526062, 10.1002/cbic.200700128, and (iii) the use of small, non-chiral auxiliaries to predictably direct P450 oxidation.{{Citation needed|date=April 2011}}

InterPro subfamilies

{{Cleanup|section|reason=broken links; fragmented paragraph.|date=September 2016}}InterPro subfamilies:
  • Cytochrome P450, B-class {{InterPro|IPR002397}}
  • Cytochrome P450, mitochondrial {{InterPro|IPR002399}}
  • Cytochrome P450, E-class, group I {{InterPro|IPR002401}}
  • Cytochrome P450, E-class, group II {{InterPro|IPR002402}}
  • Cytochrome P450, E-class, group IV {{InterPro|IPR002403}}
  • Aromatase
Clozapine, imipramine, paracetamol, phenacetin Heterocyclic aryl aminesInducible and CYP1A2 5-10% deficientoxidize uroporphyrinogen to uroporphyrin (CYP1A2) in heme metabolism, but they may have additional undiscovered endogenous substrates. are inducible by some polycyclic hydrocarbons, some of which are found in cigarette smoke and charred food.These enzymes are of interest, because in assays, they can activate compounds to carcinogens. High levels of CYP1A2 have been linked to an increased risk of colon cancer. Since the 1A2 enzyme can be induced by cigarette smoking, this links smoking with colon cancer.JOURNAL, Petros WP, Younis IR, Ford JN, Weed SA, Effects of tobacco smoking and nicotine on cancer treatment, Pharmacotherapy, 32, 10, 920–31, October 2012, 23033231, 3499669, 10.1002/j.1875-9114.2012.01117,

See also

References

{{Reflist}}

Further reading

  • JOURNAL, Gelboin HV, Krausz K, Monoclonal antibodies and multifunctional cytochrome P450: drug metabolism as paradigm, Journal of Clinical Pharmacology, 46, 3, 353–72, March 2006, 16490812, 10.1177/0091270005285200,
  • JOURNAL, Gelboin HV, Krausz KW, Gonzalez FJ, Yang TJ, Inhibitory monoclonal antibodies to human cytochrome P450 enzymes: a new avenue for drug discovery, English, Trends in Pharmacological Sciences, 20, 11, 432–8, November 1999, 10542439, 10.1016/S0165-6147(99)01382-6,weblink
  • WEB,weblink Cytochrome P450 Mediated Drug and Carcinogen Metabolism using Monoclonal Antibodies, home.ccr.cancer.gov, 2018-04-02,
  • JOURNAL, Krausz KW, Goldfarb I, Buters JT, Yang TJ, Gonzalez FJ, Gelboin HV, Monoclonal antibodies specific and inhibitory to human cytochromes P450 2C8, 2C9, and 2C19, Drug Metabolism and Disposition, 29, 11, 1410–23, November 2001, 11602516,weblink
  • JOURNAL, Gonzalez FJ, Gelboin HV, Role of human cytochromes P450 in the metabolic activation of chemical carcinogens and toxins, Drug Metabolism Reviews, 26, 1–2, 165–83, 1994, 8082563, 10.3109/03602539409029789,

External links

{{Commons category|Cytochrome P450}} {{Hemeproteins}}{{Cytochrome P450}}{{Enzymes}}

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