Nicotinamide mononucleotide adenylyltransferase 2 (NMNAT2) catalyzes the formation of NAD+ from nicotinamide mononucleotide (NMN) and ATP. Can also use the deamidated form nicotinic acid mononucleotide (NaMN) as a substrate but with lower efficiency. NMNAT2 also catalyzes the reverse reaction, i.e. the pyrophosphorolytic cleavage of NAD+. It is highly expressed in brain, in particular in cerebrum, cerebellum, occipital lobe, frontal lobe, temporal lobe and putamen. NMNAT2 is also found in the heart, skeletal muscle, pancreas and islets of Langerhans. NMNAT2 is essential for axon growth and survival. Its loss from injured axons may activate Wallerian degeneration (axon degeneration induced by nerve injury), whereas NMNAT overexpression rescues axons from degeneration.