Arylamines are a ubiquitous group of chemical agents that influence human health in a variety of ways. In particular, the mutagenic and carcinogenic properties of arylamines are of concern. Environmental and dietary arylamines have been shown to produce breast cancer, intestinal cancer and liver cancer in animals, as well as bladder cancer in humans. Mammalian acetyltransferase enzymes play critical roles in the detoxification, bioactivation and disposition of carcinogenic arylamines and their metabolites. This investigation has two major objectives. One objective is to gain insight into the molecular basis of the catalytic mechanism, active site topology and substrate specificity of carcinogen metabolizing hamster hepatic acetyltransferase isozymes by identifying critical peptide and amino acid residues and, ultimately, elucidating their contribution to catalysis and binding. The second major objective is to identify the specific arylamine-peptide adducts formed as a result of the reaction of acetyltransferase- bioactivated carcinogenic arylhydroxamic acids with the acetyltransferases. Interactions between reactive, bioactivated carcinogens and the specific enzymes that catalyze the bioactivation reactions may be important factors in the disposition of carcinogens. Thus, identification of enzyme-carcinogen adducts will contribute to definitive characterization of the chemical mechanisms through which the bioactivated carcinogens react with their biological targets and will add to the understanding of the structure and catalytic mechanisms of these important enzymes. Isozyme-selective affinity labels will be synthesized in radiolabeled form and will be used as active site directed irreversible inactivators of hamster hepatic monomorphic N-acetyltransferase. The affinity labeled enzymes will be characterized by enzymatic digestion and identification of the affinity labeled amino acid and peptide residues. Radiolabeled carcinogenic arylhydroxamic acids will be synthesized and used as mechanism based irreversible inactivators (suicide inactivators) of the monomorphic acetyltransferase isozyme; the structures of the covalently modified amino acid residues and peptides will be identified. The cDNA for the hamster hepatic polymorphic acetyltransferase isozyme will be cloned, characterized and expressed to provide sufficient quantities of the protein for future research with affinity labels and mechanism based inhibitors, and for more extensive studies of active site topology and catalytic mechanisms.
NIH ExPorter
NIH ExPorter