title: Selective binding of amino acid residues to tRNAPhe.
abstract: The interaction of amino acid amides with tRNAPhe was studied by measurements of the Wye base fluorescence. Binding of phenylalanine-, tyrosine- and tryptophan-amides leads to considerable quenching, whereas the amides of e.g. glycine and leucine do not induce quenching under the same conditions. Binding constants at 0.13 M salt - 100 M-1 for Phe-, 110 M-1 for Tyr- and 300 M-1 for Trp-amide - are about a factor of 6 higher than those evaluated from independent measurements for binding to simple single-stranded polynucleotides; the corresponding factor is 10 for double-stranded polynucleotides. Since the apparent enthalpy changes derived from measurements at different temperatures remains relatively low (-9 to -20 kJ/mol), the increased affinity appears to be mainly due to an increase of the entropy changes. Titration experiments performed in the presence of Mg2+ indicate cooperative interactions of the aromatic residues with the anticodon loop that are consistent with preferential binding to one of two loop conformations. Measurements of binding constants at different pH-values indicate the protonation of a tRNA residue in the tryptophanamide-tRNAPhe complex characterised by a pK value of about 7.0.
mesh_terms: D000494:Allosteric Regulation; D000596:Amino Acids / Q000378:metabolism*; D006863:Hydrogen-Ion Concentration; D007700:Kinetics; D008274:Magnesium / Q000378:metabolism; D008954:Models, Biological; D009994:Osmolar Concentration; D010649:Phenylalanine; D011485:Protein Binding; D012343:RNA, Transfer / Q000378:metabolism*; D012441:Saccharomyces cerevisiae; D013696:Temperature
chemical_list: D000596:Amino Acids; D010649:Phenylalanine; D012343:RNA, Transfer; D008274:Magnesium