[Fluorescence spectroscopy studies of interactions of leucyl-tRNA-synthetase with substrates].

Interactions of leucyl-tRNA synthetase with substrates were studied by fluorescence spectroscopy. The formation of enzyme-substrate complexes results in the quenching of protein fluorescence. The equilibrium binding constants were determined for L-leucine, ATP, tRNAleu and leucyladenylate. It is shown that the interaction of the enzyme with ATP or tRNAleu leads to 10-30-fold increase in the binding constants for subsequent interaction of the second substrate. The data obtained indicate to the cooperative interaction between ATP and tRNA binding sites.