Studies on valyl-tRNA synthetase obtained from chick embryo brain. Purification and properties.

Valyl-tRNA synthetase (L-valine tRNA ligase (AMP) E. C. 6.1 . 1.9) from chick embryo brain was isolated by two chromatographic steps from the cytosol fraction of brain homogenates. The protein was found to be more than 90 per cent homogeneous on the basis of polyacrylamide gel electrophoresis. It had a molecular weight of 110,000 daltons determined by both high speed equilibrium centrifugation and gel filtration. No evidence was found for a subunit structure. The optimum reaction conditions as well as the kinetic constants for ATP, valine and tRNA were determined. Enzyme stability during storage as a function of temperature and in the presence and absence of polyhydric alcohols is described. Polyhydric alcohols were found to protect the enzyme from inactivation.