cytochrome P450

Cytochrome P450 is the body's master workshop for chemically altering drugs. Think of a versatile factory crew that can grab almost any incoming molecule and clip an oxygen atom onto it, making it easier to dispose of. This crew handles the majority of drug oxidation in the body.

P450s are a superfamily of heme-containing enzymes embedded in the smooth endoplasmic reticulum, most abundantly in liver hepatocytes. Their name comes from the 450-nanometer light absorption peak of their carbon-monoxide-bound heme. They are organized by family and subfamily (e.g., CYP3A4, CYP2D6, CYP2C9), and just a handful of isoforms account for most drug metabolism.

Because so many drugs share these enzymes, P450s are the crossroads of drug interactions. One drug can induce or inhibit a P450 and dramatically change the blood levels of another. Genetic differences in P450 genes also explain why some patients are 'fast' or 'slow' metabolizers of the same medication.