[Catalytic activity of isolated cytochromes P-450d and P-450c]. / Kataliticheskaia aktivnost' izolirovannykh tsitokhromov P-450d i P-450c.

Cytochrome P-450d was isolated from isosafrol-induced rat liver microsomes by affinity chromatography on 1.8-diaminooctyl-Sepharose 4B and chromatography on hydroxylapatite using a linear potassium phosphate gradient (45-250 mM). The enzyme has a molecular mass of 54 kDa, CO-maximum 448 nm is characterized by a high spin state; the rate of 4-aminobiphenyl hydroxylation is 54 nmol/min/nmol of cytochrome P-450d (37 degrees C), those, of 7-ethoxyresorufin O-deethylation and benz (a) pyrene oxidation are 1 nmol/min/nmol of cytochrome P-450d (22 degrees C) and 2 nmol/min/nmol of cytochrome P-450d (37 degrees C), respectively. The properties of cytochrome P-450d were compared to those of cytochrome P-450c isolated from 3-methylcholanthrene-induced rats. The yield of these cytochromes under the conditions used (10% P-450d from isosafrol-induced microsomes and 15% P-450c from 3-methylcholanthrene-induced microsomes) was relatively high. Antibodies to cytochromes P-450d and P-450c were obtained. Using rocket immunoelectrophoresis the percentage of these hemoprotein forms in 3-methylcholanthrene-induced (P-450d-20%, P-450c-70%) and isosafrol-induced rat liver microsomes (P-450d-50%, P-450c-15%) was determined.

[Relation between the 7-ethoxyresorufin-O-deethylase activity of the liver microsomal monooxygenase system and the level of methylcholanthrene-induced form of cytochrome P-450]. / Sootnoshenie mezhdu 7-étoksirezorufin-O-deétilaznoi aktivnost'iu mikrosomnoi monooksigenaznoi sistemy pecheni i kontsentratsiei metilkholantrenindutsiruemoi formy tsitokhroma P-450.

Changes in the metabolic activity of 7-ethoxyresorufin in rat liver microsomes containing different amounts of cytochrome P-450 induced by 3-methylcholanthrene and other polycyclic hydrocarbons (P-450c) were studied. Using antibodies to cytochrome P-450c for the determination of the cytochrome P-450c content and its metabolic role, it was demonstrated that 7-ethoxyresorufin O-deethylation by the liver microsomal monooxygenase system is catalyzed exclusively by cytochrome P-450c. The rate of the substrate metabolism is correlated with the cytochrome P-450c content in microsomal membranes; the cytochrome P-450c activity does not depend on the cytochrome P-450c/NADPH-cytochrome P-450 reductase ratio. The experimental results suggest that the level of 7-ethoxyresorufin metabolism in liver microsomes can be regarded as a measure of the cytochrome P-450c content, whose function is associated with the stimulation of potential carcinogenic and toxic substances.