Branched chain amino acids as activators of branched chain ketoacid dehydrogenase

During purification of branched chain ketoacid dehydrogenase from Pseudomonasputida, large losses in enzyme activity occurred. Much of the activity was restored by the addition of a heat-treated, soluble fraction. The factor had a molecular weight less than 1000 and, of several potential effectors tested, the branched chain amino acids were the only compounds which stimulated enzyme activity, with valine being the most effective. The concentration of valine in the heat-treated fraction was found to be sufficient to account for all of the stimulation produced by this fraction. Valine had no effect on either pyruvate or 2-ketoglutarate dehydrogenases.