Properties and substrate specificity of the leucyl-, the threonyl- and the valyl-transfer-ribonucleic acid synthetases from Aesculus species

摘要

p1. Leucyl- and threonyl-tRNA synthetases were partially purified up to 100-fold and 30-fold respectively from cotyledons of iAesculus hippocastanum/i and were largely separated from the other aminoacyl-tRNA synthetases. Valyl-tRNA synthetase was purified 25-fold from cotyledons of iAesculus californica/i. 2. Some properties are reported for the three enzymes when assayed by the [sup32/supP]pyrophosphate-ATP exchange technique. 3. β-(Methylenecyclopropyl)alanine, isoleucine, azaleucine, norleucine and γ-hydroxynorvaline acted as alternative substrates for the leucyl-tRNA synthetase; the enzyme9s affinity for β-(methylenecyclopropyl)-alanine and for isoleucine was about 80-fold less than that exhibited for leucine. 4. α-Cyclopropylglycine and α-cyclobutylglycine acted as alternative substrates for the valyl-tRNA synthetase./p