Specific positions involved in enzyme catalyzed covalent binding of benzo[a]pyrene to poly(G)

Covalent binding of benzo[a]pyrene to poly(G) was studied with the use of a radioactive assay and specifically labeled substrates to define the role of the 1, 3- and 6-positions of the hydrocarbon during this process. Binding was shown to be dependent on microsomes, NADPH, O2 and poly(G). 7, 8-Benzoflavone and 2', 2'-diethylaminoethyl-2, 2-diphenyl valerate were inhibitory w.hereas modulators of epoxide hydrase activity had little effect. 3H and 14C studies suggested a possible loss of one to two protons. Incorporation of [6-3H1]benzo[a]pyrene provided evidence that the 6-position of the hydrocarbon was not metabolized during covalent attachment to poly(G) and, furthermore, results with [1, 3, 6-3H]benzo[a]pyrene suggest that the 1- and 3-positions may not be involved either. After scaling up of the standard assay 20-fold, characterization of the tritiated BaP-poly(G) complex was carried out by hydrolysis and subsequent chromatography. Thin-layer chromatography of the isolated hydrolysis products treated with HCl or alkaline phosphatase indicated that the complex formed between BaP and poly(G) was covalently linked and composed of hydrocarbon-nucleotide(s).