Purification and characterization of pulmonary cytochrome P-450 from 3-methylcholanthrene-treated rats.

A major form of pulmonary cytochrome P-450 (pulmonary P-450MC) was purified approximately 313 fold from lung microsomes of 3-methylcholanthrene (MC)-treated rats. The purified preparation contained 12.5 nmol of cytochrome P-450 per mg protein and was essentially free from NADPH-cytochrome c-reductase, NADH-cytochrome b5-reductase, and cytochrome b5. By SDS-polyacrylamide gel electrophoresis, the molecular weight of pulmonary P-450MC was estimated to be 54,000, which is smaller than that of a major form of hepatic cytochrome P-450 (hepatic P-450MC) purified from MC-treated rats. The peptide patterns of the purified pulmonary P-450MC were apparently different from those of hepatic P-450MC on partial proteolysis with either S. aureus V8 protease or papain, indicating that the primary structure of pulmonary P-450MC is different from that of hepatic P-450MC. In reconstituted systems, pulmonary P-450MC efficiently catalyzed benzo(a)pyrene hydroxylation and ethoxycoumarin O-deethylation, but showed a low activity for benzphetamine N-demethylation. Pulmonary P-450MC formed a single precipitation line with the antibody prepared against hepatic P-450MC in Ouchterlony double diffusion analysis. The pulmonary and hepatic P-450MC activities of benzo(a)pyrene hydroxylation and ethoxycoumarin O-deethylation were inhibited in the same manner by the antibody against hepatic P-450MC. These results suggest that pulmonary P-450MC is immunologically very similar to hepatic P-450MC.