Abstract
1. Factors affecting aminoacyl-tRNA synthesis in vitro by cell-free preparations from bean leaves were investigated. 2. Evidence was obtained that optimum concentrations as well as correct ratios of Mg(2+) and ATP are required for aminoacyl-tRNA synthesis in the bean-leaf system. 3. The results indicated that pH is a controlling factor having differential effects on the formation of individual aminoacyl-tRNA species. The possible micro-regulatory function of pH in protein synthesis in vivo is discussed with special reference to alanyl-tRNA formation. 4. Very low rates of alanine-stimulated pyrophosphate exchange were observed in the absence of tRNA. This observation is discussed relative to proposals about the mechanism of aminoacyl-tRNA synthesis.