Cytochrome P450 enzymes

Cytochrome P450 enzymes

Most of the Phase I reactions are caused by the cytochrome P450 microsomal oxidase system. There are 18 families of cytochrome P450 genes with 43 subfamilies (more genes have been identified but their function is unknown). Each enzyme is identifiable by the abbreviation CYP followed by the class (number) and then subfamily (letter) and gene (number).

CYP 1, 2, 3 families are known to metabolize

lipophilic drugs and the most important 8 are shown in the figure. The remaining enzymes synthesize or degrade other lipophilic compounds such as cholesterol, bile acids, hormones, etc.

It is often important to know if a drug is a “substrate”, “inhibitor” or “inducer” of a particular enzyme system.