Purification and Properties of Lysyl Transfer Ribonucleic Acid Synthetase from Bakers' Yeast

Lysyl transfer ribonucleic acid synthetase (L-lysine: tRNA ligase (AMP), EC 6.1.1.6)was pursed to a state of apparent homogeneity from bakers' yeast.For each of two different preparation procedures, a 250-to 500-fold purikation of the enzyme was obtained, and the final purification step yielded two distinct protein components with specific activity values of approximately 0.5 and 1.0 pmole of lysyl-tRNA formed per min per mg of protein at 30'.The major component showed the higher specific activity in the aminoacylation reaction, was free from aminoacyl-tRNA synthetases other than lysyl-tRNA synthetase, gave a single protein boundary on sedimentation in the analytical ultracentrifuge, and showed one band on polyacrylamide gel electrophoresis.Both enzyme components appeared to be acidic proteins.Amino acid analysis of the major component showed a high content of aspartic and glutamic acid residues.The two protein components were distinguished by their difference in electrophoretic mobility on starch and polyacrylamide gels and by position of elution on ion exchange columns.Both components catalyzed lysine-dependent exchange of azPpyrophosphate into ATP in the absence of lysine-acceptor RNA, each showing the same specific activity value of approximately 3 rmoles of inorganic pyrophosphate exchanged per min per mg of protein at 30'.Both showed similar apparent &, values for each of the substrates in the aminoacylation reaction and the ATP-PPi exchange reaction.The aminoacyl transfer ribonucleic acid synthetases have attracted wide interest because of the high specificity with which they catalyze the reactions which lead to the biosynthesis of proteins (l-3).As part of an investigation of the structure and function of lysine-acceptor ribonucleic acid, we have recently purified lysyl-tRNA synthetase (L-lysine: tRNA ligase (AMP), EC 6.1.1.6)from bakers' yeast.In each of two different purification procedures, the final step yielded two distinct but similar protein components possessing Lys-tRNA1 synthetase activity.