Selective loss of pulmonary cytochrome P-450I in rabbits pretreated with polychlorinated biphenyls

The polychlorinated biphenyls mixture, Aroclor 1254, generally considered a powerful inducer of rat hepatic and pulmonary microsomal monooxygenases, caused a 70% decrease in ethylmorphine N-demethylase activity, a 31% decrease in benzo(a)pyrene hydroxylase activity, and a 42% decrease in cytochrome P-450 content in rabbit lung microsomes. When pulmonary cytochrome P-450 was solubilized and subjected to column chromatography, the elution profiles of the two forms of the hemeprotein showed a marked decrease in cytochrome P-450I in treated rabbits, with no significant alteration in cytochrome P-450II content. These data were confirmed by subjecting the two cytochromes to gel electrophoresis and staining the electrophoretic bands for protein and heme-associated peroxidase activity. Cytochromes P-450I and P-450II isolated from Aroclor 1254-treated rabbits showed differences in spectral properties as well as in their stabilities. The CO difference spectral determinations showed absorbance maxima at 452 and 450 nm for cytochromes P-450I and P-450II, respectively. At room temperature, cytochrome P-450II was much more stable than P-450I. The present studies provide evidence not only for species differences in the biological actions of the polychlorinated biphenyls but also demonstrate differential effects of the environmental pollutant on the two major forms of cytochrome P-450 and associated enzymic activities in rabbit lungs.     

Chromatographic and catalytic properties of multiple forms of rabbit pulmonary cytochromes P-450

Rabbit pulmonary cytochrome P-450 forms 2,5, and 6 were resolved using anion-exchange high-performance liquid chromatography (HPLC) and their properties compared with rabbit liver cytochrome P-450 isozymes LM₂ and LM₆. Although rabbit pulmonary form 2 and liver LM₂ had similar electrophoretic mobilities and similar substrate specificities in reconstitution experiments, they differed in their HPLC elution profiles. High-performance liquid chromatography of pulmonary microsomes from rabbits treated with 3-methylcholanthrene (3-MC) revealed the induction of form 6 isozyme, which had a retention time, electro-phoretic mobility, and substrate specificity similar to those of rabbit liver LM₆. In reconstitution experiments, forms 2 and 6 showed the highest substrate specificities toward benzphetamine and 7-ethoxyresorufin, respectively. Rabbit lung cytochrome P-450 form 5 was relatively inactive toward all substrates tested.