Pathway Human Homo sapiens

Cytochrome P450 - arranged by substrate type

R-HSA-211897 in Reactome release 97: under Phase I - Functionalization of compounds, with 67 genes placed in it by the mapping files and 6 child pathways in the hierarchy.

The same number in the other species

Reactome writes the mouse and rat events it infers from a human pathway under the human number with the species token. A door opens only where that species' own list in this release holds the id: R-MMU-211897 (mouse), R-RNO-211897 (rat). Whether the event was inferred from this one is what the record says.

The record
The genes
Parents and children

Scripts are off

This page reads the pathway's record from its source while you read the rest; with scripts off the card stays at its loading line. Reload with scripts on to see it, or open the source's own page from the link in the card.

01The record

Reactome's own record of this pathway

What this tells you

The pathway list, the hierarchy and the genes on this page are read from the files Reactome publishes for Reactome release 97, built into this site on 2026-09-09: the pathway list, the hierarchy relationship file and the two gene mapping files. The record card is the one live read, Reactome's own record of this pathway.

Reactome's download page describes the mapping files: Mapping files link the source database identifier to the lowest level pathway diagram or subset of the pathway, all levels of the pathway hierarchy or database identifier to all reactions. [R13] The gene list here is the all-levels mapping of NCBI Gene ids, filled from the all-levels mapping of Ensembl ids where the NCBI file has no row for a gene; each row names which file it came from by the shape of its source id. Each row carries the evidence codes the file writes for it, as written and unranked, and both where the file writes both; no page of Reactome's documentation the survey read defines the codes, so this page does not expand them. A gene id the identity files do not name is kept as the source's own id with no door rather than turned into a symbol.

On citing what a search finds, Reactome says: It should be remembered that while we strive to contain the most current and accurate data, Reactome should not be used in citations where other primary sources of information are available. [R12] The record card prints the literature Reactome attaches to a curated pathway for that reason. The data are public domain: All data in the Reactome database and files derived from that data are licensed under the Creative Commons Public Domain Dedication (CC0). User may copy, modify, and distribute these data, even for commercial purposes, without asking for permission. Attribution is encouraged but not required. [R10] The pathway illustrations are licensed apart, under CC BY 4.0, and none is shown here.

A gene on this list is one Reactome places in this pathway in this release, and that is all the row says: it does not say the gene is expressed in a tissue or associated with a disease, which are the other two explorers' questions, read from other sources. Reactome's papers of record are [R01] [R02].

[R01] Ragueneau E, Gong C, Sinquin P, Sevilla C, Beavers D, Grentner A, et al. (2026). The Reactome Knowledgebase 2026. Nucleic Acids Research 54:D673-D681. PMID 41251150, doi 10.1093/nar/gkaf1223.
[R02] Milacic M, Beavers D, Conley P, Gong C, Gillespie M, Griss J, et al. (2024). The Reactome Pathway Knowledgebase 2024. Nucleic Acids Research 52:D672-D678. PMID 37941124, doi 10.1093/nar/gkad1025.
[R10] Reactome, reactome.org. License Agreement. https://reactome.org/license, read 2026-09-09.
[R12] Reactome, reactome.org. Citing us. https://reactome.org/cite, read 2026-09-09.
[R13] Reactome, reactome.org. Download. https://reactome.org/download-data, read 2026-09-09.

Stable id: R-HSA-211897.6
Class: Pathway
Species: Homo sapiens (human)
Inferred: no: a curated human pathway
Disease pathway: no
Released: 2008-06-30
Last updated: 2023-09-13
Events inside: 7, counted from the record

The P450 isozyme system is the major phase 1 biotransforming system in man, accounting for more than 90% of drug biotransformations. This system has huge catalytic versatility and a broad substrate specificity, acting upon xenobiotica and endogenous compounds. It is also called the mixed-function oxidase system, the P450 monooxygenases and the heme-thiolate protein system. All P450 enzymes are a group of heme-containing isozymes which are located on the membrane of the smooth endoplasmic reticulum. They can be found in all tissues of the human body but are most concentrated in the liver. The name "cytochrome P450" (CYP) is derived from the spectral absorbance maximum at 450nm when carbon monoxide binds to CYP in its reduced (ferrous, Fe2+) state. The basic reaction catalyzed by CYP is mono-oxygenation, that is the transfer of one oxygen atom from molecular oxygen to a substrate. The other oxygen atom is reduced to water during the reaction with the equivalents coming from the cofactor NADPH. The basic reaction is; RH (substrate) + O2 + NADPH + H+ = ROH (product) + H2O + NADP+

The end results of this reaction can be (N-)hydroxylation, epoxidation, heteroatom (N-, S-) oxygenation, heteroatom (N-, S-, O-) dealkylation, ester cleavage, isomerization, dehydrogenation, replacement by oxygen or even reduction under anaerobic conditions.

The metabolites produced from these reactions can either be mere intermediates which have relatively little reactivity towards cellular sysytems and are readily conjugated, or, they can be disruptive to cellular systems. Indeed, inert compounds need to be prepared for conjugation and thus the formation of potentially reactive metabolites is in most cases unavoidable.

There are 57 human CYPs (in 18 families and 42 subfamilies), mostly concentrated in the endoplasmic reticulum of liver cells although many tissues have them to some extent (Nelson DR et al, 2004). CYPs are grouped into 14 families according to their sequence similarity. Generally, enzymes in the same family share 40% sequence similarity and 55% within a subfamily. Nomenclature of P450s is as follows. CYP (to represent cytochrome P450 superfamily), followed by an arabic number for the family, a capital letter for the subfamily and finally a second arabic number to denote the isoenzyme. An example is CYP1A1 which is the first enzyme in subfamily A of cytochrome P450 family 1.

The majority of the enzymes are present in the CYP1-4 families. CYP1-3 are primarily concerned with xenobiotic biotransformation whereas the other CYPs deal primarily with endogenous compounds. The CYP section is structured by the typical substrate they act upon. Of the 57 human CYPs, 7 encode mitochondrial enzymes, all involved in sterol biosynthesis. Of the remaining 50 microsomal enzymes, 20 act upon endogenous compounds, 15 on xenobiotics and 15 are the so-called "orphan enzymes" with no substrate identified.

The P450 catalytic cycle (picture) shows the steps involved when a substrate binds to the enzyme.

(1) The normal state of a P450 with the iron in its ferric [Fe3+] state.

(2) The substrate binds to the enzyme.

(3) The enzyme is reduced to the ferrous [Fe2+] state by the addition of an electron from NADPH cytochrome P450 reductase. The bound substrate facilitates this process.

(4,5) Molecular oxygen binds and forms an Fe2+OOH complex with the addition of a proton and a second donation of an electron from either NADPH cytochrome P450 reductase or cytochrome b5. A second proton cleaves the Fe2+OOH complex to form water.

(6) An unstable [FeO]3+ complex donates its oxygen to the substrate (7). The oxidised substrate is released and the enzyme returns to its initial state (1).

Literature Reactome attaches

Cytochrome P450s and other enzymes in drug metabolism and toxicityAAPS J, 2006, vol. 8, p. E101-11PubMed 16584116
57 varieties: the human cytochromes P450Pharmacogenomics, 2004, vol. 5, p. 305-18PubMed 15102545
The cytochrome P450 superfamily: biochemistry, evolution and drug metabolism in humansCurr Drug Metab, 2002, vol. 3, p. 561-97PubMed 12369887

Reactome's record lists 13 orthologous events, R-MMU-211897 (Mus musculus), R-RNO-211897 (Rattus norvegicus) among the species this site serves, and 11 in species this site opens no page for.

Reactome ContentService, this pathway's record · Reactome v97 · read 2026-09-30 ET · Reactome pathway browser"Cytochrome P450 - arranged by substrate type". Reactome, release 97, https://reactome.org/PathwayBrowser/#/R-HSA-211897 with StableID: R-HSA-211897.6 (accessed 2026-09-30 ET). Reactome version 97 (CC0).

Reading this pathway's record from Reactome (the pathway record).Still reading. A first read of a pathway can take a while; this page waits up to 35 seconds for it, and its scripts then bring in the panel, or a line saying what did not arrive.

02The genes

Genes Reactome places in this human pathway

The mapping files place 67 genes in this human pathway; showing 1 to 67, in pages of 100, sorted by symbol for reading. The order carries no ranking.

Genes Reactome places in this human pathway, page 1 of 1
Gene	Authority id	Mapping file id	Evidence codes
GeneADH7	AuthorityHGNC:256	Mapping file id131 NCBI file	EvidenceTAS
GeneAHR	AuthorityHGNC:348	Mapping file id196 NCBI file	EvidenceTAS
GeneAHRR	AuthorityHGNC:346	Mapping file id57491 NCBI file	EvidenceTAS
GeneARNT	AuthorityHGNC:700	Mapping file id405 NCBI file	EvidenceTAS
GeneARNT2	AuthorityHGNC:16876	Mapping file id9915 NCBI file	EvidenceTAS
GeneCYP11A1	AuthorityHGNC:2590	Mapping file id1583 NCBI file	EvidenceTAS
GeneCYP11B1	AuthorityHGNC:2591	Mapping file id1584 NCBI file	EvidenceTAS
GeneCYP11B2	AuthorityHGNC:2592	Mapping file id1585 NCBI file	EvidenceTAS
GeneCYP19A1	AuthorityHGNC:2594	Mapping file id1588 NCBI file	EvidenceTAS
GeneCYP1A1	AuthorityHGNC:2595	Mapping file id1543 NCBI file	EvidenceTAS
GeneCYP1A2	AuthorityHGNC:2596	Mapping file id1544 NCBI file	EvidenceTAS
GeneCYP1B1	AuthorityHGNC:2597	Mapping file id1545 NCBI file	EvidenceTAS
GeneCYP21A2	AuthorityHGNC:2600	Mapping file id1589 NCBI file	EvidenceTAS
GeneCYP24A1	AuthorityHGNC:2602	Mapping file id1591 NCBI file	EvidenceTAS
GeneCYP26A1	AuthorityHGNC:2603	Mapping file id1592 NCBI file	EvidenceTAS
GeneCYP26B1	AuthorityHGNC:20581	Mapping file id56603 NCBI file	EvidenceTAS
GeneCYP26C1	AuthorityHGNC:20577	Mapping file id340665 NCBI file	EvidenceTAS
GeneCYP27A1	AuthorityHGNC:2605	Mapping file id1593 NCBI file	EvidenceTAS
GeneCYP27B1	AuthorityHGNC:2606	Mapping file id1594 NCBI file	EvidenceTAS
GeneCYP2A13	AuthorityHGNC:2608	Mapping file id1553 NCBI file	EvidenceTAS
GeneCYP2A6	AuthorityHGNC:2610	Mapping file id1548 NCBI file	EvidenceTAS
GeneCYP2A7	AuthorityHGNC:2611	Mapping file id1549 NCBI file	EvidenceTAS
GeneCYP2B6	AuthorityHGNC:2615	Mapping file id1555 NCBI file	EvidenceTAS
GeneCYP2C18	AuthorityHGNC:2620	Mapping file id1562 NCBI file	EvidenceTAS
GeneCYP2C19	AuthorityHGNC:2621	Mapping file id1557 NCBI file	EvidenceTAS
GeneCYP2C8	AuthorityHGNC:2622	Mapping file id1558 NCBI file	EvidenceTAS
GeneCYP2C9	AuthorityHGNC:2623	Mapping file id1559 NCBI file	EvidenceTAS
GeneCYP2D6	AuthorityHGNC:2625	Mapping file id1565 NCBI file	EvidenceTAS
GeneCYP2E1	AuthorityHGNC:2631	Mapping file id1571 NCBI file	EvidenceTAS
GeneCYP2F1	AuthorityHGNC:2632	Mapping file id1572 NCBI file	EvidenceTAS
GeneCYP2J2	AuthorityHGNC:2634	Mapping file id1573 NCBI file	EvidenceTAS
GeneCYP2R1	AuthorityHGNC:20580	Mapping file id120227 NCBI file	EvidenceTAS
GeneCYP2S1	AuthorityHGNC:15654	Mapping file id29785 NCBI file	EvidenceTAS
GeneCYP2U1	AuthorityHGNC:20582	Mapping file id113612 NCBI file	EvidenceTAS
GeneCYP2W1	AuthorityHGNC:20243	Mapping file id54905 NCBI file	EvidenceTAS
GeneCYP39A1	AuthorityHGNC:17449	Mapping file id51302 NCBI file	EvidenceTAS
GeneCYP3A4	AuthorityHGNC:2637	Mapping file id1576 NCBI file	EvidenceTAS
GeneCYP3A43	AuthorityHGNC:17450	Mapping file id64816 NCBI file	EvidenceTAS
GeneCYP3A5	AuthorityHGNC:2638	Mapping file id1577 NCBI file	EvidenceTAS
GeneCYP3A7	AuthorityHGNC:2640	Mapping file id1551 NCBI file	EvidenceTAS
GeneCYP3A7-CYP3A51P	AuthorityHGNC:51504	Mapping file id100861540 NCBI file	EvidenceTAS
GeneCYP46A1	AuthorityHGNC:2641	Mapping file id10858 NCBI file	EvidenceTAS
GeneCYP4A11	AuthorityHGNC:2642	Mapping file id1579 NCBI file	EvidenceTAS
GeneCYP4A22	AuthorityHGNC:20575	Mapping file id284541 NCBI file	EvidenceTAS
GeneCYP4B1	AuthorityHGNC:2644	Mapping file id1580 NCBI file	EvidenceTAS
GeneCYP4F11	AuthorityHGNC:13265	Mapping file id57834 NCBI file	EvidenceTAS
GeneCYP4F12	AuthorityHGNC:18857	Mapping file id66002 NCBI file	EvidenceTAS
GeneCYP4F2	AuthorityHGNC:2645	Mapping file id8529 NCBI file	EvidenceTAS
GeneCYP4F22	AuthorityHGNC:26820	Mapping file id126410 NCBI file	EvidenceTAS
GeneCYP4F3	AuthorityHGNC:2646	Mapping file id4051 NCBI file	EvidenceTAS
GeneCYP4F8	AuthorityHGNC:2648	Mapping file id11283 NCBI file	EvidenceTAS
GeneCYP4V2	AuthorityHGNC:23198	Mapping file id285440 NCBI file	EvidenceTAS
GeneCYP51A1	AuthorityHGNC:2649	Mapping file id1595 NCBI file	EvidenceTAS
GeneCYP7A1	AuthorityHGNC:2651	Mapping file id1581 NCBI file	EvidenceTAS
GeneCYP7B1	AuthorityHGNC:2652	Mapping file id9420 NCBI file	EvidenceTAS
GeneCYP8B1	AuthorityHGNC:2653	Mapping file id1582 NCBI file	EvidenceTAS
GeneFDX1	AuthorityHGNC:3638	Mapping file id2230 NCBI file	EvidenceTAS
GeneFDX2	AuthorityHGNC:30546	Mapping file id112812 NCBI file	EvidenceTAS
GeneFDXR	AuthorityHGNC:3642	Mapping file id2232 NCBI file	EvidenceTAS
GeneNCOA1	AuthorityHGNC:7668	Mapping file id8648 NCBI file	EvidenceTAS
GeneNCOA2	AuthorityHGNC:7669	Mapping file id10499 NCBI file	EvidenceTAS
GeneNR1H4	AuthorityHGNC:7967	Mapping file id9971 NCBI file	EvidenceTAS
GenePOMC	AuthorityHGNC:9201	Mapping file id5443 NCBI file	EvidenceTAS
GenePOR	AuthorityHGNC:9208	Mapping file id5447 NCBI file	EvidenceTAS
GenePTGIS	AuthorityHGNC:9603	Mapping file id5740 NCBI file	EvidenceTAS
GeneRXRA	AuthorityHGNC:10477	Mapping file id6256 NCBI file	EvidenceTAS
GeneTBXAS1	AuthorityHGNC:11609	Mapping file id6916 NCBI file	EvidenceTAS

Evidence codes on this page: TAS, as the mapping file writes them; a row carrying two was written twice by the file, once under each. The mapping file id says which file placed the gene: an NCBI Gene id from NCBI2Reactome_All_Levels.txt, an Ensembl gene id from Ensembl2Reactome_All_Levels.txt. The two files can disagree about a code, so a row's codes are the one file's view. Measured by this site's build over this release on 2026-09-09: of the 138,908 human pathway-gene pairs both files place, 207 (0.149 per cent, over 47 genes) carry TAS in the Ensembl file where the NCBI rows carry IEA alone.

Reactome mapping files, the human rows for this pathway · Reactome release 97 · read 2026-09-09 · Reactome downloads"NCBI2Reactome_All_Levels.txt" and "Ensembl2Reactome_All_Levels.txt", Reactome, release 97, https://reactome.org/download-data/ (date of access 2026-09-09). Data CC0; attribution encouraged.

03The hierarchy

Parents and children in this release's hierarchy

Parents

Phase I - Functionalization of compoundsR-HSA-211945106 genes

Children

Reactome's hierarchy is a graph rather than a tree: a pathway can sit under more than one parent, and the gene counts are each pathway's own placements at every level under it, so a parent's count is not the sum of its children's.

Reactome, the human pathway list and hierarchy relationship file · Reactome release 97 · read 2026-09-09 · Reactome downloads"ReactomePathways.txt" and "ReactomePathwaysRelation.txt", Reactome, release 97, https://reactome.org/download-data/ (date of access 2026-09-09). Data CC0; attribution encouraged.