Involved in the regulation of the intracellular balance of NAD and NADP, and is a key enzyme in the biosynthesis of NADP. Catalyzes specifically the phosphorylation on 2'-hydroxyl of the adenosine moiety of NAD to yield NADP. It can use ATP and other nucleoside triphosphates (GTP,UTP) as well as inorganic polyphosphate (poly(P)) as a source of phosphorus. NAD is the preferred substrate for the kinase, but NADH can also be used as phosphoryl acceptor. ATP + NAD(+) = ADP + H(+) + NADP(+) Optimum pH is 6.8. At 70 degrees Celsius for 60 minutes, the enzyme does not lose activity in a pH range of 4.0 to 10.5. Extremely high thermostability. Upon heating at 95 degrees Celsius for 10 minutes the kinase activity is not lost, but about 80% of the activity is lost upon incubation at 100 degrees Celsius for 10 minutes. Homotetramer. Belongs to the NAD kinase family.