抄録
Isoleucyl-tRNA synthetase (IRS) was partially purified from an extreme thermophile, T. thermophilus HB 8. The molecular weight (11.5×104) and some kinetic constants were obtained and compared with IRS from other sources.
The present IRS catalyzed both isoleucine dependent and valine dependent ATP-PP1 exchange reactions (optimum at around 80°C) but not valyl-tRNA formation. The optimum temperature for isoleucyl-tRNA formation was 62°C with E. coli tRNA and 75°C with T. thermophilus tRNA.
The enzyme showed a remarkable thermostability. The addition of E. coli or T. thermophilus tRNA enhanced the thermostability of the enzyme, which was shown to be fully active up to 77°C. When E. coli tRNA was used, the loading activity decreased in parallel to the unfolding of the substrate tRNA molecule. From these results the relation is discussed between tRNA conformation and function.
