Threonyl-tRNA, Lysyl-tRNA and Arginyl-tRNA Synthetases from Baker's Yeast. Substrate Specificity with Regard to ATP Analogues

Abstract
Sixteen analogs of ATP were tested in the aminoacylation reaction of threonyl-tRNA, lysyl-tRNA and arginyl-tRNA synthetases from baker''s yeast. Two compounds are substrates for threonyl-tRNA and for lysyl-tRNA synthetases and 5 compounds for arginyl-tRNA synthetase. These are 6 inhibitors for threonyl-tRNA, 9 for lysyl-tRNA and 6 for arginyl-tRNA synthetase. Their Km and Ki values were determined. Thus positions 2, 6, 7, 8 and 9 of the purine moiety and 2'' and 3'' of the sugar moiety of the ATP molecule are important for catalytic action of these aminoacyl-tRNA synthetases. Remarkably arginyl-tRNA synthetase is the 1st aminoacyl-tRNA synthetase which tolerates bulky substituents at the sugar moiety of ATP. These data fit with the idea that synthetases of subunit structure need Mg2+-ATP complexes with an anti conformation as substrates whereas single-chain enzymes accept this substrate in the syn conformation.

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