Reversible interconversion of two forms of a valyl-tRNA synthetase-containing protein complex.

When an enzyme-containing complex from yeast was incubated in a buffered solution at room temperature, the valyl-transfer RNA synthetase activity and total protein oscillated synchronously between two physical states. This observation suggests a regulatory process that controls a number of enzymes as a group, an integrated function of a kind not heretofore recognized. The two forms of the complex were separated by ammonium sulfate precipitation of one of them in samples withdrawn from the incubated solution every 30 seconds. Glutathione and dithiothreitol in high concentrations (50 mM) enhance formation of the 50% saturated ammonium sulfate-soluble form. Oxidized glutathione, diphosphopyridine nucleotide, triphosphopyridine nucleotide, and a mercurial thiol binding agent in moderate concentrations (0.1 to 1.0 mM) shift the distribution toward the precipitable form. It is suggested that the two forms represent functional and nonfunctional complex-bound enzymes which are interconverted in response to oxidoreductive signals.