Valyl-tRNA synthetase from rabbit liver. I. Purification as a heterotypic complex in association with elongation factor 1.

Valyl-tRNA synthetase occurs as a high molecular mass entity of approximately equal to 700 kDa in the crude extract from rabbit liver. The enzyme was purified as a heterotypic complex comprising four polypeptides of 140, 50, 35, and 27 kDa in the molar proportions of 1:2:1:1, respectively, as determined by one-dimensional sodium dodecyl sulfate-polyacrylamide gel electrophoresis. Co-purification of these components at each step of the purification supports the conclusion that they are physically associated within the same complex. In addition to valyl-tRNA synthetase activity, which was assigned to the 140-kDa component, the purified complex exhibits a potent Elongation Factor 1 activity, determined by its ability to sustain poly(U)-dependent polyphenylalanine synthesis in the presence of Elongation Factor 2. Our results are essentially in agreement with those from a recent report (Motorin, Y., Wolfson, A., Orlovsky, A., and Gladilin, K. (1988) FEBS Lett. 238, 262-264), according to which the polypeptides other than that assigned to valyl-tRNA synthetase correspond to the subunits of Elongation Factor 1H.