One of the key enzymes of the pyridine nucleotide cycle which permits cells to recycle the by products of NAD consumption back to NAD. Has no activity on NAD, NADP, nicotinamide or nicotinamide riboside. beta-nicotinamide D-ribonucleotide + H2O = NH4(+) + nicotinate beta-D-ribonucleotide Optimum pH is 5.5-9.0. Homodimer. Not essential for growth on defined medium, loss of NMN amidohydrolase activity. Belongs to the CinA family.