The cytochrome P450 superfamily. The function of most CYP enzymes is to catalyze the oxidation of organic substances. The most common reaction catalyzed by cytochromes P450 is a monooxygenase reaction. RH (organic substrate) + O2 + 2H+ + 2eâ€“ â†’ ROH + H2O. CYP families in humans divided among 18 families of cytochrome P450 genes and 43 subfamilies.