1,3-Dinitrobenzene metabolism and protein binding.

Abstract

1,3-Dinitrobenzene is a testicular toxicant, which produces a lesion in the seminiferous tubules of the rat. In the present study, we investigated which subcellular fractions of the seminiferous tubules are capable of 1,3-dinitrobenzene metabolism and protein adduct formation. Subcellular fractions of the liver were used as positive controls and to further investigate potentially important binding proteins. Microsomes, cytosol, and mitochondria prepared from each tissue were incubated with 200 microM [(14)C]1,3-dinitrobenzene and 2 mM NADH or NADPH. Since nitroreduction is an oxygen sensitive metabolic pathway, incubations were carried out in the presence and absence of oxygen. Under anaerobic conditions, 1,3-dinitrobenzene was metabolized to nitroaniline and/or nitrophenylhydroxylamine. Metabolite formation was inhibited under aerobic conditions, suggesting the presence of an oxygen-dependent redox-cycle. For the seminiferous tubules, no metabolites were generated under aerobic conditions. In the absence of oxygen, only the mitochondria produced 1,3-dinitrobenzene metabolites. For the liver, under anaerobic conditions, all three subcellular fractions produced 1,3-dinitrobenzene metabolites with the microsomes containing the greatest activity. However, under aerobic conditions, only the microsomes generated metabolites. One-dimensional gel electrophoresis demonstrated that protein adduct formation within the liver and seminiferous tubule subcellular fractions correlated with metabolite formation. Addition of GSH to seminiferous tubule mitochondrial incubations decreased the amount of (14)C-labeled protein. Moreover, when seminiferous tubule mitochondria were incubated with 1,3-dinitrobenzene at an increased protein concentration, radioactive labeling of a 54 kDa protein became more prominent. Two-dimensional gel electrophoresis of liver mitochondrial protein incubated with [(14)C]1,3-dinitrobenzene and NADPH yielded three predominantly radiolabeled proteins of the same approximate size (54 kDa). Amino acid sequencing identified each of these proteins as rat mitochondrial aldehyde dehydrogenase.