Catalyzes the ATP-dependent amidation of deamido-NAD to form NAD. Uses ammonia as a nitrogen source. ATP + deamido-NAD(+) + NH4(+) = AMP + diphosphate + H(+) + NAD(+) Optimum pH is 8. Cofactor biosynthesis; NAD(+) biosynthesis; NAD(+) from deamido-NAD(+) (ammonia route): step 1/1. Homodimer. Belongs to the NAD synthetase family.