CYP

CYP, short for cytochrome P450, refers to a large and diverse family of heme-containing monooxygenase enzymes found in bacteria, fungi, plants, and animals, including humans. They catalyze the insertion of one atom of oxygen into a wide range of substrates while the other oxygen atom is reduced to water. Electron supply for the reaction typically comes from NADPH via a dedicated reductase and, in some cases, cytochrome b5.

In humans, CYP enzymes are primarily expressed in the liver and intestine and are central to drug metabolism. The most clinically important families are CYP1, CYP2, and CYP3, with representatives such as CYP3A4, CYP2D6, CYP2C9, and CYP2C19. CYP3A4 is a major contributor to the metabolism of many drugs. Genetic variations in these enzymes lead to differences in enzymatic activity, giving rise to phenotypes such as poor, intermediate, extensive, or ultrarapid metabolizers, which can influence drug efficacy and risk of adverse effects.

Structure and mechanism: Cytochrome P450 enzymes contain a heme group with an iron atom coordinated by a cysteine ligand. Substrate binding can trigger changes that enable binding and activation of molecular oxygen. The catalytic cycle involves electron transfer from NADPH through P450 reductase (and sometimes cytochrome b5), formation of highly reactive intermediates, and insertion of an oxygen atom into the substrate.

Physiological and clinical relevance: Beyond drug metabolism, CYP enzymes participate in biosynthesis of cholesterol, steroids, and bile acids, as well as in the metabolism of endogenous lipids and environmental chemicals. Inhibitors or inducers of CYP activity can cause drug–drug interactions, and pharmacogenomic testing for certain CYPs informs personalized therapeutic choices.