Fluorimetric Study of the Complex between Yeast Phenylalanyl‐tRNA Synthetase and tRNAPhe

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Abstract
The variations of several spectroscopic properties of yeast tRNAPhe and phenylalanyl-tRNA synthetase upon complex formation, were used to study the stoichiometry of the complex in different experimental conditions. In all cases, for the tRNAPhe-enzyme complex, in the absence of other ligands, the saturations of the different conformational changes monitored for both macromolecules, are achieved at a 2:1 tRNA/enzyme stoichiometry. Phenylalanine does not modify this saturation. In contrast, the presence of 1 mM ATP induces an asymmetric behavior of the synthetase: 2 tRNA are still bound per enzyme molecule but the conformational change of the latter is completed upon binding of a single tRNA molecule.