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 (By similarity). ATP + NAD(+) = ADP + H(+) + NADP(+) H2O + NADP(+) = NAD(+) + phosphate Homotetramer. In the N-terminal section; belongs to the inositol monophosphatase superfamily. In the C-terminal section; belongs to the NAD kinase family.