The measurement of FAD-containing mono-oxygenase activity in microsomes containing cytochrome P-450.

Antibodies to NADPH-cytochrome P-450 reductase have been used to essentially abolish the contribution of cytochrome P-450 to xenobiotic metabolism by mammalian microsomes. This permits the determination of the activity of the FAD-containing mono-oxygenase and the stoichiometry between substrate, O2 and NADPH, in the microsomal membrane, and in the absence of cytochrome P-450-dependent activity. FAD-containing mono-oxygenase oxidation rates were determined for sulphur- and nitrogen-containing substrates, including: thiols; sulphides; thioamides; primary, secondary and tertiary amines; hydrazines. Although the enzyme in mouse, rabbit, rat and pig microsomes displays similar substrate specificity, some catalytic characteristics are different between species and tissues.