Cation Dependence of the Transfer Reaction Catalyzed by Phenylalanyl Transfer Ribonucleic Acid Synthetase from Bakers' Yeast

Abstract

Abstract The ability of yeast phenylalanyl-tRNA synthetase to transfer the phenylalanyl moiety from its phenylalanyladenylate complex to purified yeast phenylalanine tRNA (tRNAphe) has been examined in the presence of various cations. With the assay conditions employed (10 mm Trisacetate, pH 7.2, 21°), this transfer reaction was completely dependent upon the addition of an oligovalent cation. Low concentrations of Mg2+, organic diamines, spermidine, or spermine were effective in stimulating the formation of phenylalanyl-tRNA. The concentration-dependent stimulation of the transfer reaction by Mg2+, spermidine, and spermine correlated reasonably well with the concentration-dependent enhancement of the fluorescence of tRNAphe effected by these same cations. Organic diamines (0.7 mm) exhibited a diminishing ability to stimulate the rate of the transfer reaction as the number of carbon atoms between the two amine groups increased. NaCl, at concentrations as high as 1.0 m, appeared not to stimulate the transfer reaction. In the presence of Mg2+ (0.3 mm), concentrations of NaCl greater than 0.2 m increasingly inhibited the rate of the transfer reaction. The cation-specific differences in transfer efficiency were shown not to be caused by any major variation in the stability of the phenylalanyladenylate-enzyme complex under the different ionic conditions examined. These results are consistent with those of our previous study of yeast tRNAphe (Robison, B., and Zimmerman, T. P., J. Biol. Chem., 246, 110 (1971)) in support of the hypothesis that the oligovalent cation-induced fluorescence/conformational changes of tRNAphe represent the conversion to its biologically active form, principally through the formation of tertiary structure.