On the stereochemistry of activation of phenylalanine by phenylalanyl-tRNA synthetase from baker's yeast.

Because of its chiralic alpha-phosphorus atom adenosine 5'-O-(1-thiotriphosphate) (ATPalphaS) exists in two diastereomeric forms, arbitrarily named (A) and (B). For phenylalanyl-tRNA synthetase ATPalphaS (A) is a substrate whereas ATPalphaS (B) is neither a substrate nor an inhibitor. During the ATPalphaS (A)/PPi exchange reaction with phenylalanyl-tRNA synthetase the configuration at the alpha-phosphorus is retained. The mechanistic implications of these findings are discussed. Preliminary investigations with several other aminoacyl-tRNA synthetases show that the stereochemical requirement with respect to the alpha-phosphorus of ATP is not identical for all aminoacyl-tRNA synthetases.