Involved in the regulation of the intracellular balance between NAD(H) and NADP(H), and is a key enzyme in the biosynthesis of NADP. Catalyzes the phosphorylation and dephosphorylation of NAD and NADP, respectively. Although it shows conflicting dual activities and is able to supply NADP, it seems that its physiological role is to prevent excess accumulation of NADP. Kinase can use ATP and other nucleoside triphosphates (UTP, TTP, CTP, GTP) as well as inorganic polyphosphate (poly(P)) as phosphoryl donors, however poly(P) is not considered to be the physiological phosphoryl donor. NAD is the preferred substrate for the kinase, but NADH can also be used as phosphoryl acceptor. Phosphatase can use NADP or NADPH as phosphoryl donor, but NADP is the preferred substrate. Phosphatase also has an activity toward the terminal phosphate group at C-2 of adenosine in 2'-AMP and toward the phosphate group at C-1 of fructose 1,6-bisphosphate, but not toward inositol 1-phosphate.