Desamino DPN

Taka-diastase deaminase. The product of deamination of DPN is called desamino DPN. This compound has also been prepared by treatment of DPN with nitrous acid. ... 

Coenzyme Specificity of Dehydrogenases. A number of dehydrogenases have been reported to require DPN, others are specific for TPN, and several react with both, although not necessarily at the same rate. Examples have already been cited of enzymes that catalyze identical reactions but possess different coenzyme requirements. An additional means for studying pyridine nucleotide reactions became available with desamino DPN. Certain dehydrogenases (e.g., liver alcohol dehydrogenase) react at equal rates with DPN and desamino DPN. Others (as... 

DPN. The rate of hydrolysis of desamino DPN by this enzyme is much slower than the rate with DPN or TPN. ... 

The reaction depends upon all of the components shown in equation (I). It has been proposed that an imino acid is an intermediate, but no evidence for the existence of such a compound has been reported. If a nonenzymatic reaction between ammonia and a-ketoglutarate were to form the true substrate, the apparent requirements for enzyme saturation should be equivalent for both compounds and the apparent requirement for each should depend on the concentration of the other, because the hypothetical imino acid would be formed in a second-order reaction of ammonia and the keto acid. Instead, a Km of 1.2 X 10 was found for a-ketoglutarate and 5.7 X 10 for NH4. Other Km values for this enzyme are 2 X 10 for glutamate, 2.5 X 10 for DPN, and 1.8 X 10 for DPNH. These values are influenced by ions in the medium and pH, and are not fixed properties of the enzyme. As with other enzymes that use both DPN and TPN, glutamic dehydrogenase also acts with desamino DPN and acetylpyridine DPN. 

These investigators were able to show that an electron rather than a phosphate transfer was involved. With desamino DPN (prepared by enzymatic hydrolysis of the 6-amino group of adenine), which can replace DPN in this reaction, the product in the case of electron transfer would be desamino DPNH2, whereas in the case of phosphate transfer it would be desamino TPN. The occurrence of the reaction ... 

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