Abstract
The mechanism of cleavage of the pyrimidinyl-phosphate bond of 32P- and pyrimidine-2- 14C-labeled diazinon or 32P-labeled diazoxon by soluble enzyme preparations from rat liver and fat body of American cockroach was studied. The reaction products were identified as diethyl phosphorothioic acid and S-(2-isopropyl-4-methyl-6-pyrimidinyl) glutathione, which were formed by conjugation of reduced glutathione and the pyrimidinyl moiety of diazinon with the simultaneous cleavage of the phosphate ester bond. Several tissues in cockroach and rat were active in this conjugation, but the highest activity was found in the fat body and the liver. The glutathione S-transferase catalyzing the conjugation was specific for glutathione, and could not be replaced by other SH compounds. Diazoxon, n-propyl, and isopropyl diazinons having the structure similar to diazinon were also cleaved to give the glutathione conjugates. The pH optimum was 6.5 for the fat body and 6.0 for the liver enzyme. Both enzymes were inhibited by various SH reagents, oxidized glutathione, and some chelating agents. The fat body enzyme showed marked sensitivity to inhibition by o-phenanthroline.
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