FLUORESCENCE STUDY OF INTERACTIONS BETWEEN VALYL-TRNA SYNTHETASE AND VALINE-SPECIFIC TRNAS FROM ESCHERICHIA COLI

Substrate-induced fluorescence variations have been used to study the association of valyl-tRNA synthetase (VRS) and tRNAval. The binding of tRNA to the enzyme leads to a decrease of the enzyme fluorescence quantum yield. A ten-fold increase in the binding constant was observed when the pH was lowered from 7.0 to 5.5. The fluorescence quantum yield of VRS alone decreases when the pH is lowered; a pK of 5.9 is obtained from the fluorescence titration curve. This suggests that ionization of residues with a pK of 5.9 (probably histidine) leads to an increase in the affinity of VRS for tRNA. It is also shown that two different species of tRNAval from E. coli differ in their affinities for the enzyme by a factor of ten. © 1969.