Purification and subunit structure studies of human placental threonyl‐tRNA synthetase

Abstract

Human threonyl-tRNA synthetase has been purified from full-term placenta over 5000-fold with a 13% overall yield by a combination of affinity chromatographic methods and conventional procedures. The product was apparently homogeneous by the criterion of sodium dodecyl sulfate-polyacrylamide gel electrophoresis. The purified enzyme catalyzed the esterification of -3500nmol L-threonine t o tRNA per min per mg of protein at 37O, corresponding t o a molecular activity of -700/min. The apparent molecular weight of the native enzyme ranged from 210 000 to 220 000 by gel-filtration on Sephadex G-200, and was either -11 0 000 or 228 000 by sucrose gradient centrifugation for different preparations. Sodium dodecyl sulfate-polyacrylamide gel electrophoresis demonstrated a single band of molecular weight 85 000 or 1 15 000 for different preparations. These results suggest that human placental threonyl-tRNA synthetase has a subunit structure of the type a2 with a subunit molecular weight of about 100000. However, some other molecular forms with lower specific activity were also found t o exist under certain conditions.

Kinetic mechanism of threonyl‐tRNA synthetase from human placenta

“…Human threonyl-tRNA synthetase was purified from placenta and assayed according to the procedures of Pan et al (4).…”