In vivo and in vitro effects of methylmercury on the activities of aminoacyl-tRNA synthetases in rat brain.

The activities of six aminoacyl-tRNA synthetase species were determined using enzyme preparations partially purified from the brains of control and methylmercury (MeHg)-treated rats. The activities of Asp-, Leu- and Tyr-tRNA synthetases were significantly reduced in the brains of MeHg-intoxicated rats, whereas those of Lys- and Met-tRNA synthetases remained unchanged. In contrast, the activity of His-tRNA synthetase was significantly increased in the symptomatic phase of MeHg intoxication. The activities of these six aminoacyl-tRNA synthetases in the control brains were affected to different extents on the direct addition of MeHg to the assay system in vitro. No positive correlation was observed between the in vivo and in vitro effects of MeHg on the enzyme activities. These results indicate that the aminoacylation of tRNA is one of the actions of MeHg, which leads to inhibition of protein synthesis, and it is suggested that the syntheses of cellular proteins may be modified in different ways by MeHg, depending on their amino acid compositions.