Alternative substrates for glutamate dehydrogenases

Summary The amide group of glutamine functions as a nitrogen donor in the reactions catalyzed by both the NADP-specific glutamate dehydrogenase of Neurospora crassa and the bovine liver enzyme, but not by the NAD-specific Neurospora enzyme. Asparagine serves as nitrogen source only for the NADP-specific Neurospora dehydrogenase. The optimum for utilization of the amide substrates is at pH 8.4 with both enzymes as contrasted to the value of pH 7.6 to 7.8 obtained with ammonia as the source of nitrogen. The maximal rate of reaction with ammonia is 2.5 times greater than that with glutamine and 10 times greater than that with asparagine at the respective pH optima. Acetamide does not serve as a source of nitrogen for either of these two enzymes.