Threonyl-tRNA synthetase from bovine liver. Purification and kinetic properties in the ATP-pyrophosphate exchange reaction.

Threonyl-tRNA synthetase (E.C. 6.1.1.3) from bovine liver has been purified to near homogeneity approximately 500 fold with a recovery of 48%. Two bands of molecular weight 90,000 and 82,000 respectively, were obtained by sodium dodecyl sulfate gel electrophoresis. The enzyme has an isoelectric point of 5.2 by polyacrylamide containing ampholine gel electrophoresis. Optimum assay conditions and apparent Km values have been determined in the ATP-PPi exchange reaction. Effects of divalent cations and diamine in substitution to Mg2+ and effects of sulfhydryl reagents on ATP-PPi exchange activity have also been observed.