Effect of chronic administration of morphine on mouse brain aminoacyl-tRNA synthetase and tRNA-amino acid binding

Abstract

Summary Effects of the chronic administration of morphine to mice on the activity of aminoacyl-tRNA synthetase and the amino acid-tRNA binding were investigated. Aminoacyl-tRNA synthetase and tRNAs were purified partially from brains of control mice and mice chronically treated with increasing doses of morphine (up to 100 mg/kg). The partially purified brain synthetase from the control and morphine-treated mice catalyzed thein vitro binding of [14C]labeled arginine, leucine and phenylalanine with unfractionated tRNAs obtained fromE. coli, mouse brains and mouse liver. However, the synthetase purified from the brains of the morphine-treated mice had lower specific activities than that purified from the brains of control mice. The decreased specific activities of synthetase of brains of morphine-treated mice were fairly proportional to the doses of morphine administered and persisted for 5 days after withdrawal of morphine. Administration of a single dose of morphine produced no significant decrease in synthetase activity. Moreover, chronic administration of morphine did not significantly alter physico-chemical properties and amino acid-binding capacities of tRNAs from the brains of mice chronically treated with morphine. Morphine did, however, moderately inhibit the binding of amino acids withE. coli tRNA in the presence of synthetase isolated from brains of either control mice or morphine-treated mice. The pretreatment of purified synthetase with morphine caused slight decreases of synthetase activity. Morphine did not bindin vivo with synthetase or tRNA in the presence of synthetases isolated from brains of either control mice or morphine-treated mice. The pretreatment of purified synthetase with morphine caused slight decreases of synthetase activity. Morphine did not bindin vivo with synthetase or tRNA during chronic administration of morphine nor with purified synthetase or tRNAin vitro.