The Interaction of Phenylalanyl Transfer Ribonucleic Acid Synthetase and Phenylalanine Transfer Ribonucleic Acid

Phenylalanyl transfer ribonucleic acid synthetase and phenylalanine transfer ribonucleic acid from Escherichia coli form complexes below pH 6.5 in sucrose gradients. The stoichiometry of the complex is 1 mole of synthetase per mole of tRNA and is specific for tRNAphe. At pH 5.0, the complex has an association constant of 1 x 107 m-1. The interaction between synthetase and tRNA was also measured by the marked quenching of the fluorescence of the tryptophan residues of the synthetase. The quenching is specific for tRNAphe. It was found that at pH 5.0 a concentration of tRNA 10-fold in excess of that needed to produce maximum complex formation on sucrose gradients was required to produce maximum fluorescence quenching.