Deamido NAD

NAD+ synthetase (ammonia-utilizing) [EC 6.3.1.5] catalyzes the reaction of ATP with deamido-NAD+ and ammonia to produce NAD+, AMP, and pyrophosphate (or, diphosphate). NAD+ synthetase (glutamine-utilizing) [EC 6.3.5.1] catalyzes the reaction of ATP with deamido-NAD+, glutamine, and water to produce NAD+, glutamate, AMP, and pyrophosphate. 

This enzyme [EC 2.7.7.1], also known as NAD pyropho-sphorylase, catalyzes the reaction of ATP with nicotinamide ribonucleotide to produce NAD+ and pyrophosphate (or, diphosphate). Nicotinate nucleotide is also a substrate. Nicotinate-nucleotide adenylyltransferase [EC 2.7.7.18] uses nicotinate ribonucleotide as the pyridine substrate, thereby producing deamido-NAD and pyrophosphate. 

Conversion of nicotinic acid to NAD is illustrated by the following experiment involving mice (Figure 9.63). The animals were injected with carbon-14-labeled nicotinic acid. The livers were removed at the indicated times — 0.33,1.0,3.0, and 10 minutes — and used for analysis of the radioactive metabolites. At 20 seconds, unchanged nicotinic acid (O) was the major metabolite. At 1 to 3 minutes, there was a temporary accumulation of nicotinic acid ribonucleotide (V) and deamido-NAD (A). NAD ( ) was the major metabolite after 3 minutes. 

NaAD nicotinic acid adenine dinucleotide or deamido-NAD... 

NAD is the active form of a vitamin, nicotinamide. The evidence available indicates that nicotinic acid is the intermediate in NAD synthesis. Thus, if the vitamin nicotinamide is used for NAD synthesis, it is used only after deamination. Nicotinic acid reacts with PRPP to yield the mononucleotide of nicotinic acid which forms deamido NAD in the presence of ATP and an enzyme present in liver nuclei. The amida-tion of the deamido NAD occurs in the presence of ATP, glutamine, and an enzyme present in the supernatant of liver homogenates. 

Thus, in the cell, the newly synthesized NAD is faced with several foes, and the cell must either provide NAD at a rate more rapid than that at which the coenzyme is hydrolyzed, or the new NAD must be kept separate from the catabolic enzymes. The intracellular distribution of the enzymes involved in NAD metabolism, therefore, is of capital interest. The enzyme that catalyzes the formation of deamido NAD from ATP and nicotinic acid mononucleotide is in the nucleus, as was first shown by Hogeboom and Schneider [93]. Later, Elyane Baltus also demonstrated that, at least in the starfish, this reaction is restricted to the nucleolus [94]. 

Nicotinic acid mononucleotide reacts with ATP in the presence of nicotinic acid adenine dinucleotide pyrophosphorylase, a magnesium-dependent enzyme, to yield the deamido derivative of NAD (see Fig. 4-11). Deamido NAD, in the presence of ATP, glutamine, Mg, K", and an NAD synthetase, is converted to NAD. In this reaction, the amino group of glutamine is transferred to the carboxyl group of the nicotinic acid moiety of deamido NAD. Yet the nicotinamide moiety of NAD synthetase is found in liver supernatant and, as may be expected, it is inhibited by azaserine. 

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