The Effect of Adenylic Acid on Yeast Nicotinamide Adenine Dinucleotide Isocitrate Dehydrogenase, a Possible Metabolic Control Mechanism.

The nicotinamide adenine dmucleotide-specific isocitrate dehydrogenase of yeast was reported by Kornberg and Pricer (1) to have an absolute requirement for adenylic acid and not to catalyze the reverse reaction under conditions suitable for such catalysis by the nicotinamide adenine dinucleotide phosphatespecific enzyme. Similar results have been obtained for the nicotinamide adenine dinucleotide enzyme of Aspergillus (2), but variable slight stimulation by adenosine 5’-phosphate, rather than an absolute requirement, has been reported for the enzyme from animal sources (3). In contrast, the nicotinamide adenine dinucleotide-specific enzymes of Acetobacter aceti (4) and of pea seedlings (5) are apparently not affected by adenosine 5’-phosphate although reversibility was not demonstrated in either case. In studies on the NAD-specific isocitrate dehydrogenase of Acetobacter peroxydans we were unable to demonstrate any effect of adenylic acid and the enzyme-catalyzed reaction was found to be freely reversible. Because of the difference between these properties and those of the yeast enzyme, we reinvestigated the latter enzyme. Adenylic acid was found not to be required for enzymic activity but to affect very markedly the rate of the reaction under some conditions. These properties are described in this paper along with the conditions under which reversal of the reaction may be observed. Partial purification and some properties of the enzyme from Acetobacter peroxydans are also reported.