Cytochrome P450 isoform (CYP (with specific isoforms typically indicated as CYP1A2, CYP2D6, CYP3A4, etc.))

The cytochrome P450 isoforms (CYPs) constitute a large superfamily of heme-containing enzymes present in nearly all domains of life and are especially abundant in the human liver and small intestine[1][5][6]. They catalyze the oxidative metabolism of a wide range of endogenous compounds (steroids, fatty acids) and exogenous substances (including most drugs), primarily via monooxygenase reactions that introduce an oxygen atom into substrates, making them more water-soluble for elimination[1][2]. These isoforms are classified into families (e.g., CYP1, CYP2, CYP3), with further subfamily and individual enzyme designation (e.g., CYP3A4, CYP2C9)[2][5]. CYPs are central to drug metabolism and are a major source of pharmacokinetic variability and drug-drug interactions, as some drugs are substrates, inhibitors, or inducers of specific CYP enzymes[2][3][6]. Genetic polymorphisms in specific isoforms (such as CYP2D6 and CYP2C19) underlie significant ethnic and inter-individual variability in drug response and adverse reactions[6]. Clinical consequences include altered efficacy or toxicity of drugs, especially agents metabolized by CYP3A4, CYP2C9, CYP2C19, and CYP2D6[2][3]. “Cytochrome P450 isoforms” as a group does not correspond to a single molecular entity, but refers to a large family of related enzymes with similar structure and conserved mechanism[1].

Other names

Cytochrome P450P450sCYPsP450 enzymes

Substrate oxidation (functionalization of drugs and endogenous substrates) Drug activation/inactivation Inhibition (competitive, noncompetitive, or mechanism-based inhibition) Induction (increasing enzyme expression to affect drug clearance)