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

1. Leucyl- and threonyl-tRNA synthetases were partially purified up to 100-fold and 30-fold respectively from cotyledons of Aesculus hippocastanum and were largely separated from the other aminoacyl-tRNA synthetases. Valyl-tRNA synthetase was purified 25-fold from cotyledons of Aesculus californica. 2. Some properties are reported for the three enzymes when assayed by the [(32)P]pyrophosphate-ATP exchange technique. 3. beta-(Methylenecyclopropyl)alanine, isoleucine, azaleucine, norleucine and gamma-hydroxynorvaline acted as alternative substrates for the leucyl-tRNA synthetase; the enzyme's affinity for beta-(methylenecyclopropyl)-alanine and for isoleucine was about 80-fold less than that exhibited for leucine. 4. alpha-Cyclopropylglycine and alpha-cyclobutylglycine acted as alternative substrates for the valyl-tRNA synthetase.