P450enzymer

Cytochrome P450 enzymes, commonly abbreviated as P450s or CYPs, are a large family of heme-containing monooxygenases that oxidize a wide range of substrates. In humans they metabolize xenobiotics, pharmaceuticals and many endogenous compounds, including steroids, fatty acids and bile acids.

Most P450s are located in the endoplasmic reticulum of liver cells, anchored to the membrane; a subset localizes to mitochondria and participates in steroidogenesis. They operate with NADPH-cytochrome P450 reductase to transfer electrons from NADPH to the heme, enabling monooxygenation: RH + O2 + NADPH + H+ → ROH + H2O + NADP+. One oxygen atom is inserted into the substrate.

In humans, CYP1–CYP3 families are most involved in drug metabolism. CYP3A4/5 handles a large share of drugs, while CYP2D6, CYP2C9 and CYP2C19 are also important. Other family members contribute to steroid biosynthesis, vitamin D metabolism and detoxification. Genetic variation in CYP genes can yield poor, intermediate, extensive or ultrarapid metabolizer phenotypes.

Expression is regulated by nuclear receptors (PXR, CAR) and is inducible by many xenobiotics; inhibitors or inducers can markedly alter drug pharmacokinetics, causing interactions. Environmental and disease factors also modulate activity.

Clinical relevance: understanding P450 function informs pharmacology, toxicology and pharmacogenomics, guiding drug development, dosing and personalized medicine.