Abstract

Enzyme components and activities of the cytochrome P-450 monooxygenase system in microsomal preparations from the Clara cell, alveolar type II cell, and alveolar macrophage fractions isolated from lungs of untreated rabbits and rabbits treated with 2,3,7,8-tetrachlorodibenzo-p-dioxin were examined. Results are compared to those obtained with microsomal preparations from whole lung. Concentrations of cytochrome P-450 isozymes 2 and 5 and NADPH-cytochrome P-450 reductase activities were higher in preparations from Clara cell fractions than in preparations from type II cell fractions or whole lung. For the most part, however, differences among these preparations were 2-fold or less. Microsomal preparations from the macrophage fraction contained low or undetectable levels of cytochrome P-450 isozymes but relatively high levels of cytochrome P-450 reductase activity. The concentration of cytochrome P-450 isozyme 6, in contrast to those of isozymes 2 and 5, was found to be highest in microsomal preparations from whole lung. Treatment of rabbits with 2,3,7,8-tetrachlorodibenzo-p-dioxin increased the concentrations of isozyme 6 in preparations from the Clara and type II cell fractions and from whole lung about 20-fold. In contrast, the content of isozyme 6 in preparations from the macrophage fraction increased greater than 90-fold. In all cases, induction of isozyme 6 resulted in substantial increases in the O-deethylation of 7-ethoxyresorufin and only minor increases in the hydroxylation of benzo(a)pyrene. Activities per unit of isozyme 6, following induction, were similar in all preparations, and we estimate that less than 20% of the potential activity of isozyme 6 is expressed with benzo(a)pyrene and greater than 40% with 7-ethoxyresorufin. These similarities exist in spite of significant differences among the preparations from different fractions in the ratios of isozyme 6 to NADPH-cytochrome P-450 reductase.