The aim of this study was to examine the effects of zinc ions on activities of tRNA(Leu) and leucyl-tRNA synthetase of mice liver.
Material and methods: White laboratory mice (20-25 g) were used for study purposes. Animals were intoxicated with ions of zinc by injection of 0.15 LD50 dose of zinc sulphate solution (1.56 mg Zn2+ per 1 kg of body weight) into abdominal cavity. After 8 hours, preparations of total tRNA and aminoacyl-tRNA synthetases were isolated from the intoxicated and normal (control) mice liver. Acceptor activity of tRNA(Leu) and activity of leucyl-tRNA synthetase were determined in tRNA aminoacylation reaction using [14C]-labeled leucine. Actions of zinc 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 zinc sulphate solution.
Results: It was determined that acceptor activity of mice liver tRNA( Leu)8 hours after intoxication with zinc ions has increased by 29% and activity of leucyl-tRNA synthetase has increased by 20% as compared to control. Experiments in vitro have shown that 5-20 microM concentrations of zinc ions in reaction mixture stimulate the acceptor activity of mice liver tRNA(Leu)by 18-30%, higher concentration of zinc ions (40 microM)--suppresses it by 26%. The study of leucyl-tRNA synthetase activity in vitro has shown that 5-10 microM concentrations of zinc ions in reaction mixture increase activity of this enzyme by 11-16%, higher concentrations of zinc ions (20-40 microM)--decrease it by 13-21%.
Conclusions: After 8-hour intoxication with zinc ions the activities of both studied components of the translation machinery--tRNA(Leu) and leucyl-tRNA synthetase were increased. It may be connected with the stimulation of zinc-binding metallothionein synthesis which is involved in the detoxification of heavy metals. Low concentrations of zinc 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 zinc ions directly act on the activities of both components of translation machinery.