Phenylalanyl-tRNA, lysyl-tRNA, isoleucyl-tRNA and arginyl-tRNA synthetases. Substrate specificity in the ATP/PPi exchange with regard to ATP analogs.

The analogs of ATP have been 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, seven for lysyl-tRNA, two for isoleucyl-tRNA and five for arginyl-tRNA synthetase. Their Km and V values have been determined. No analog was an inhibitor. (3'-dATP), 3'-Deoxyadenosine 5'-triphosphate which is an inhibitor of the four enzymes in the aminoacylation reaction, becomes a good substrate in the PPi exchange. Additionally lysyl-tRNA synthetase accepts two analogs with modifications at position 6 of the purine and three 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.