Reactions Sequence of Leucine Activation Catalysed by Leucyl-RNA Synthetase. 2. Formation of Complexes between the Enzyme and Substrates

In order to obtain information on the sequence of reactions which participate in the activation of leucine, the formation of complexes between the leucyl-RNA synthetase and its substrates was examined. A leucyladenylate-enzyme complex able to transfer its leucine to the RNA was isolated. Likewise, an enzyme-ATP complex was separated; when re-incubated with leucine, it reacts to form the leucyladenylate-enzyme complex. The effect of leucinol, leucinol-AMP and 6-N-hydroxyethyl-ATP on the formation of these complexes was examined. The results indicate that during the activation of leucine, the leucyl-RNA synthetase first binds ATP and then reacts with leucine.