Regulation of Aryl Hydrocarbon Hydroxylase in Intraspecific Hybrids of Human, Mouse, and Hamster Cells

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Abstract
Microsomal aryl hydrocarbon (benzo{a}-pyrene) hydroxylase is an enzyme complex highly inducible by various substrates. The activity of this enzyme complex was studied in hybrid cell strains obtained from parent cells that differ widely in basal as well as in induced enzyme activity. Hybrid cells were made from mouse fibroblasts, 3T3-4C2, with moderate basal and induced enzyme activity and the L-cell subline, A9, which has no detectable hydroxylase activity. Hybrid A9/3T3-4C2 cells exhibited enhanced basal and induced enzyme activities, which were 2- to 5-fold higher than those in 3T3-4C2 cells. In contrast, intraspecific hybrid cells of the human cell lines, JEC-3 and VA-2, and the hamster cell lines, OBP and BHK, exhibited a reduced basal and induced enzyme activity that was similar to or lower than that of the parent with low enzyme activity. In all hybrid cells examined, an association was observed between basal and induced enzyme activities, suggesting a closely coupled regulation of these activities.