Nucleic Acids Research, 1984, Vol. 12, No. 19 7549-7563
© 1984
CHEMISTRY |
Selective binding of amino add residues to tRNAPhe
Max-Planck-Institut für biophysikalische Chemie 3400 Göttingen, FRG
Received July 17, 1984. Accepted September 13, 1984.
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 asides of e.g. glycine and lencine do not induce quenching nnder the sane 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 aromatio 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 tENA residue in the tryptophanamido-tRNAPhe oomplex characterised by a pK value of about 7.0.
*On leave from Department of Biopolymer Biochemistry, Pozna
University, 61-701 Pozna, Poland