A. Viviani, Werner K. Lutz

• The lnfluence of mlcrosomal and nuclear aryl hydrocarbon hydroxylase (AHH) actlvlty on the covalent blndlng of [G·3H]benzo(a )pyrene to rat llver DNA was evaluated in viWJ. lnductlon of mlcrosomal AHH was obtalned alter phenobarbltal treatment (160% of control), whlch also lncreased DNA blndlng to 190%, but left the nuclear actlvlty unchanged. Nuclear AHH was lnduced wlth dleldrln (150%), and the blndlng was decreased to 75%, whereaa the mlcrosomal AHH was at control Ievei. The lncreaslng effect of mlcrosomal AHH lnductlon as weil as theThe lnfluence of mlcrosomal and nuclear aryl hydrocarbon hydroxylase (AHH) actlvlty on the covalent blndlng of [G·3H]benzo(a )pyrene to rat llver DNA was evaluated in viWJ. lnductlon of mlcrosomal AHH was obtalned alter phenobarbltal treatment (160% of control), whlch also lncreased DNA blndlng to 190%, but left the nuclear actlvlty unchanged. Nuclear AHH was lnduced wlth dleldrln (150%), and the blndlng was decreased to 75%, whereaa the mlcrosomal AHH was at control Ievei. The lncreaslng effect of mlcrosomal AHH lnductlon as weil as the decreaslng effect of nuclear AHH lnductlon on the blndlng was shown clearly when the data of the Individual rata were uaed to solve the equatlon Binding = e•(mlcroeomal AHH) + b•(nuclear AHH) + c Multiple linear regresslon analysls wlth the data from 10 anlmala reaulted ln positive valuea for a and c, a negative value for b, and a good multiple correlatlon coefflclent of r = 0.974. Pretreatment wlth 3-methylcholanthrene ln· duced mlcrosomal AHH to 380% of control and nuclear AHH to 590% and lncreased the blndlng' to 175,.-o. The blndlng was hlgher than predlcted by the formula found, probably because the lncreaslng lnfluence of lnduced mlcrosomal AHH overahadowed the decreaslng effect of the nuclear AHH. The study ahows clearly that the blndlng of a forelgn compound to DNA in viWJ Ia dependent not only on mlcrosomal enzyme actlvltles but also on nuclear actlvltles even lf the latter are conslderably lower than thoae of mlcrosomes.…