Nicotinamide/nicotinate-nucleotide adenylyltransferase that acts as an axon maintenance factor (By similarity). Catalyzes the formation of NAD(+) from nicotinamide mononucleotide (NMN) and ATP (PubMed:16118205, PubMed:17402747). Can also use the deamidated form; nicotinic acid mononucleotide (NaMN) as substrate but with a lower efficiency (PubMed:16118205, PubMed:17402747). Cannot use triazofurin monophosphate (TrMP) as substrate (PubMed:16118205, PubMed:17402747). Also catalyzes the reverse reaction, i.e. the pyrophosphorolytic cleavage of NAD(+) (PubMed:16118205, PubMed:17402747). For the pyrophosphorolytic activity prefers NAD(+), NADH and NaAD as substrates and degrades nicotinic acid adenine dinucleotide phosphate (NHD) less effectively (PubMed:16118205, PubMed:17402747). Fails to cleave phosphorylated dinucleotides NADP(+), NADPH and NaADP(+) (PubMed:16118205, PubMed:17402747). Axon survival factor required for the maintenance of healthy axons: acts by delaying Wallerian axon degeneration, an evolutionarily conserved process that drives the loss of damaged axons (By similarity). ATP + beta-nicotinamide D-ribonucleotide + H(+) = diphosphate + NAD(+) ATP + H(+) + nicotinate beta-D-ribonucleotide = deamido-NAD(+) + diphosphate Divalent metal cations. Mg(2+) confers the highest activity. Inhibited by P1-(adenosine-5')-P3-(nicotinamide-riboside-5')-triphosphate (Np3AD) and P1-(adenosine-5')-P4-(nicotinamide-riboside-5')-tetraphosphate (Np4AD). KM is >100 uM for triazofurin monophosphate. Optimum pH is 6.0-9.0. Cofactor biosynthesis; NAD(+) biosynthesis; NAD(+) from nicotinamide D-ribonucleotide: step 1/1. Cofactor biosynthesis; NAD(+) biosynthesis; deamido-NAD(+) from nicotinate D-ribonucleotide: step 1/1. Monomer. Delivered to axons with Golgi-derived cytoplasmic vesicles. Highly expressed in brain, in particular in cerebrum, cerebellum, occipital lobe, frontal lobe, temporal lobe and putamen. Also found in the heart, skeletal muscle, pancreas and islets of Langerhans. Degraded in response to injured neurite. Degradation is probably caused by ubiquitination by MYCBP2 (By similarity). Ubiquitinated on threonine and/or serine residues by MYCBP2; consequences of threonine and/or serine ubiquitination are however unclear (PubMed:29643511). Palmitoylated; palmitoylation is required for membrane association. Belongs to the eukaryotic NMN adenylyltransferase family. Extended N-terminus.