[Cytochrome P450 isoenzymes in metabolism of endo- and exogenic compounds].

Cytochrome P450 enzymes (CYPs) belong to hemeproteins found in all living organisms. In eucaryotic cells they are responsible for biosynthesis and transformations of endogenic lipids as well as for the metabolism of xenobiotics, including therapeutic agents. C-Oxidation (hydroxylation, epoxydation, peroxydation), N-oxidation and S-oxidation as well as oxidative O-, S-, and N-dealkylation of substrates are catalysed by CYPs. These monooxygenation reactions sometimes result in dimerisation, isomerisation or cyclisation of the substrate. Human cytochrome P450 isoenzymes are described by 57 genes and products of their expression are different in specificity. For instance CYP51A1 is crucial for sterol biosynthesis, whereas CYP7A1, 7B1 and 39A1 take part in synthesis of bile acids and CYP46A1 in metabolism of cholesterol. Therapeutic agents are metabolised mainly by CYP3A4, 2D6, 2C9 and 2C19. In addition, CYP2E1 takes part in metabolism of ethyl alcohol and CYP1A1/2 in activation of carcinogens. Metabolism of xenobiotics seems to be the defence mechanism against toxic effects of strange chemicals, whereas, it is also the way of drug activation and detoxication.