[Effects of lead ions on activities of tRNALeu and leucyl-tRNA synthetase of mouse liver].

Unlabelled: The objective of this study was to examine effect of lead ions on activities of mice liver tRNA(Leu) and leucyl-tRNA synthetase.
Material and Methods: For researching white non-breed laboratory mice (20-25 g) were used. Intoxication with ions of lead was performed by injection of sublethal dose of lead acetate solution (50 mg ions of lead per 1 kg of body weight) into abdominal cavity of laboratory animals. Eight hours after intoxication from intoxicated and normal (control) mice liver preparations of tRNA and aminoacyl-tRNA synthetases were isolated. Acceptor activity of tRNA(Leu) and activity of leucyl-tRNA synthetase were determined in tRNA aminoacylation reaction using [(14)C]-labeled leucine. Actions of lead ions on acceptor activity of tRNA(Leu) and on activity of leucyl-tRNA synthetase from liver of control animals in vitro were determined after addition into reaction mixture different concentrations of lead acetate solution.
Results: It was determined that acceptor activity of mice liver tRNA(Leu) 8 h after intoxication with lead ions was reduced by 37 percent and activity of leucyl-tRNA synthetase was increased by 22 percent as compared to control. Experiments in vitro have shown that 10 micro M concentration of lead ions in reaction mixture stimulate acceptor activity of mice liver tRNA(Leu) by 17 percent, higher concentrations of lead ions (30-60 microM)--suppress it by 9-80 percent. The study of leucyl-tRNA synthetase activity in vitro has shown that 30 microM concentration of lead ions in reaction mixture increases activity of this enzyme by 16 percent, higher concentrations of lead ions (40-60 microM)--decrease by 17-23 percent.
Conclusions: After 8 h intoxication with lead ions acceptor activity of tRNA(Leu) was decreased and activity of leucyl-tRNA synthetase was increased. It may be part of the compensatory mechanism of the cell to keep synthesis of proteins at the normal level under extreme conditions. Low concentrations of lead ions in reaction mixture increase tRNA(Leu) and leucyl-tRNA synthetase activities, higher concentrations of these ions decrease activity of those components of protein synthesis system. The results show that ions of lead directly suppress activity of both components of translation machinery.