PURIFICATION AND CHARACTERIZATION OF TYROSYL-RNA SYNTHETASE OF BAKERS YEAST

Tyrosyl-tRNA synthetase [EC 6. 1. 1. 1] was purified from baker's yeast. The purified preparation had no cross reaction with 19 other amino acids. Three kinds of assay involving hydroxamate formation, ATP-PP1 exchange and tyrosyl-tRNA formation were adopted to characterize the enzyme. It was observed that the Km values for tyrosine obtained with the above three methods were not the same. Among many tyrosine analogues only 3-iodo-tyrosine and D-tyrosine stimulated the ATP-PP1 exchange reaction, while tyrosol and tyramine were competitive inhibitors. Based on these results it was concluded that the hydroxyl group at the para-position and the α-amino group of the substrate have an essential role in binding to the enzyme.The effects of several metal ions upon enzymatic activity were studied. The effects differed remarkably depending upon the assay methods. © 1968 by the Journal of Biochemistry.