Phosphorylates both NAD(+) and NADH, with a twofold preference for NADH. Source of the cellular reductant NADPH which is an important antioxidant factor. ATP + NAD(+) = ADP + H(+) + NADP(+) ATP + NADH = ADP + H(+) + NADPH Measured at pH 7.9 and 25 degrees Celsius for all experiments. Optimum pH is 7.9 at 25 degrees Celsius. A number of isoforms are produced. According to EST sequences. Ubiquitous. Expressed during development from young seedlings to flowering plants. By gamma radiation, hydrogen peroxide and infection by P.syringae. Belongs to the NAD kinase family.