cytochroomP450enzymen

Cytochrome P450 enzymes, commonly abbreviated CYP or CYP450, are a superfamily of heme-containing monooxygenases found in virtually all organisms. They catalyze the insertion of one atom of molecular oxygen into a substrate (monooxygenation), using reducing equivalents from NADPH via a membrane-associated heme protein and its reductase partner. The catalytic cycle involves activation of O2 to Compound I and transfer of an oxygen atom to the substrate, yielding a hydroxylated product and water.

Most human CYP enzymes are localized to the endoplasmic reticulum of hepatocytes and enterocytes, though several mitochondrial P450s participate in steroidogenesis, drug metabolism, and other pathways. Microsomal P450s rely on NADPH-cytochrome P450 reductase; mitochondrial P450 systems use adrenodoxin/adrenodoxin reductase.

Humans express many CYP families, including major drug-metabolizing isoforms such as CYP3A4 (with broad substrate range, responsible for a substantial share of drug metabolism), CYP2D6, CYP2C9, CYP2C19, and CYP1A2. Beyond detoxification, CYPs participate in endogenous pathways: steroid biosynthesis (CYP11A1, CYP17A1, CYP19A1), bile acid synthesis (CYP7A1), and fatty-acid metabolism (various CYPs).

Genetic variation in CYP genes underpins pharmacogenomic differences in drug response. Polymorphisms in CYP2D6, CYP2C9, and CYP2C19 can classify individuals as poor, intermediate, extensive, or ultra-rapid metabolizers, affecting efficacy and toxicity and guiding dosing and drug selection. Inducers and inhibitors can alter activity and cause drug interactions.

Evolutionarily, the CYP superfamily has diversified widely, reflecting adaptation to dietary, environmental, and physiological substrates. They are used as model systems in toxicology and medicine and are targets for drug development and personalized medicine.