Phenylalanyl‐tRNA, Lysyl‐tRNA, Isoleucyl‐tRNA and Arginyl‐tRNA Synthetases

Abstract

Ten analogs of ATP were tested in the ATP/PPi exchange reaction of phenylalanyl-tRNA, lysyl-tRNA, isoleucyl-tRNA and arginyl-tRNA synthetases from baker''s yeast. Three compounds are substrates for phenylalanyl-tRNA, 7 for lysyl tRNA, 2 for isoleucyl-tRNA and 5 for arginyl-tRNA synthetase. Their Km and V were determined. No analog was an inhibitor. 3''-dATP, which is an inhibitor of the 4 enzymes in the aminoacylation reaction, becomes a good substrate in the PPi exchange. Additionally, lysyl-tRNA synthetase accepts 2 analogs with modifications at position 6 of the purine and 3 analogs modified at the ribose moiety as substrates in the PPi exchange, whereas these compounds are inactive or inhibitors in the aminoacylation reaction. In general the enzymes are less specific in the ATP/PPi exchange, and the results indicate a more sophisticated proof of the nucleotide moiety upon aminoacylation. This could occur with the aminoacyladenylate intermediate as well as with any other intermediate.