Assay and characterization of the enzyme system

j Microsomal preparations of Aspergillus ochraceus TS oxidised benzo(a)pyrene very efficiently in the presence of NADPH and 02 and exhibits a pH optimum of 8,0-8.2. The hydroxylation is also effected in presence of NaI04. Hydroxylation was inhibited by metyrapone, SKF-525A, PCMB, imidazole, carbon monoxide and flavone but not by cyanide, azide and antimycin A indicating thereby the involvement of cytochrome P-450 in this reaction. Inhibition by cytochrome C is consistant with the participation of NADPHcytochrome C reductase in this hydroxylation. Reduced microsomes and its solubilized preparation, when treated with carbon mono­ xide, showed absorption maxima at 453 and 449 respectively. Diffe­ rent classical inducers of cytochrome P-450 induce the benzo(a)pyrene hydroxylase activity to varying degree and as such suggests the existence of multiple forms of cytochrome P-450 in this fungus.