Abstract
Aryl hydrocarbon (benzo (a)pyrene) hydroxylase induced by dibutyryl cyclic AMP (dcAMP), plus aminophylline (AHH l) can be distinguished from the hydroxylase induced by benz (a) anthracene (AHH II) by its lower Km for benzo (a)pyrene. Treatment with the combination of benz (a) anthracene and dcAMP plus aminophylline induced both AHH I and AHH II activities. After optimal induction of AHH II activity by benz (a)anthracene, the addition of dcAMP plus aminophylline gave an induction of AHH I. Although AHH I activity declined to an almost basal level 24 h after treatment with dcAMP plus aminophylline, the addition of benz (a) anthracene prevented this decline. Inducibility by dcAMP plus aminophylline or by benz (a)anthracene varied in different cell lines. Some cell lines were induced by both substances, with a higher induction by benz (a)βanthracene, while other lines were inducible only by benz (a)anthracene, and a third cell type was not inducible by either. Selection for resistance to benzo (a)pyrene of a cell line inducible by both compounds resulted in a fourth cell type which was mase inducible by dcAMP plus aminophylline than by benz (a)anthracene. The results suggest that therΓ© is an independent regulation of hydroxylase AHH I and AHH II and that the induction of these two enzyme activities is determined by different genetic control.