MECHANISM OF THE INACTIVATION OF RAT LIVER CYTOCHROME P-450 BY PARATHION

Abstract

Publisher Summary This chapter examines the mechanism of the inactivation of rat liver cytochrome P-450 by parathion. The investigation focuses on the relationship between the loss of cytochrome P-450, the loss of benzphetamine demethylase and ethoxycoumarin de-ethylase activity, and the extent of covalent binding of sulfur to cytochrome P-450 during the metabolism of parathion by a reconstituted system from liver microsomes of phenobarbital-treated rats. The chapter also discusses the nature of the protein-bound sulfur not dissociable with DTT. Cytochrome P-450 was purified from liver microsomes of phenobarbital-treated rats. The 16% polyethylene glycol supernatant from this procedure was used as the source of the NADPH-cytochrome P-450 reductase, which was purified by ammonium sulfate precipitation and affinity chromatography on ADP 2'5' Sepharose. Metabolism of parathion by the reconstituted system was found to be accompanied by a considerable loss of heme. In a series of six experiments described in the chapter, the heme loss was calculated to be 81 ± 10% of the cytochrome P-450 loss. Catalase offered little or no protection against the loss of heme, suggesting that it was not because of hydrogen peroxide formation during the metabolism of parathion.