Activating enzymes: multiple monooxygenase forms with different substrate preferences as related to toxic effects.

The presence of multiple molecular forms of cytochrome P-450 in experimental animals and perhaps is of considerable importance in dealing with the metabolism of drugs, mutagens, carcinogens and other toxic compounds. Differences in substrate specificity, positional specificity and stereoselectivity of various forms of cytochrome P-450 play an important role in regulating the balance between activation and inactivation pathways of a given chemical. The relative proportions of various forms of cytochrome P-450 in a given tissue or individual may be an important factor in determining the cytotoxic and carcinogenic action of many toxic compounds.