Catalyzes the hydrolysis of sphingomyelin to form ceramide and phosphocholine. Ceramide mediates numerous cellular functions, such as apoptosis and growth arrest, and is capable of regulating these 2 cellular events independently. Also hydrolyzes sphingosylphosphocholine. Binds to anionic phospholipids (APLs) such as phosphatidylserine (PS) and phosphatidic acid (PA) that modulate enzymatic activity and subcellular location (By similarity). Regulates the cell cycle by acting as a growth suppressor in confluent cells. Acts as a regulator of postnatal development and participates in bone and dentin mineralization. May be involved in IL-1-beta-induced JNK activation in hepatocytes. May act as a mediator in transcriptional regulation of NOS2/iNOS via the NF-kappa-B activation under inflammatory conditions. a sphingomyelin + H2O = an N-acylsphing-4-enine + H(+) + phosphocholine H2O + N-(15Z-tetracosenoyl)sphing-4-enine-1-phosphocholine = H(+) + N-(15Z-tetracosenoyl)-sphing-4-enine + phosphocholine H2O + N-(tetracosanoyl)-sphing-4-enine-1-phosphocholine = H(+) + N-tetracosanoyl-sphing-4-enine + phosphocholine an N-(acyl)-sphingosylphosphocholine + H2O = an N-acyl-sphingoid base + H(+) + phosphocholine 1-hexadecanoyl-sn-glycero-3-phosphocholine + H2O = 1-hexadecanoyl-sn-glycerol + H(+) + phosphocholine 1-O-octadecyl-sn-glycero-3-phosphocholine + H2O = 1-O-octadecyl-sn-glycerol + H(+) + phosphocholine a sphingosylphosphocholine + H2O = a sphingoid base + H(+) + phosphocholine H2O + N-(hexadecanoyl)-sphing-4-enine-1-phosphocholine = H(+) + N-hexadecanoylsphing-4-enine + phosphocholine Inhibited by nSMase inhibitor GW4869. Binding of anionic phospholipids (APLs) such as phosphatidylserine (PS) and phosphatidic acid (PA) increases enzymatic activity. Lipid metabolism; sphingolipid metabolism. May localize to detergent-resistant subdomains of Golgi membranes of hypothalamic neurosecretory neurons (PubMed:10823942). In brain sections, it is restricted to neurons and especially prominent in large cells, including Purkinje cells, pyramidal cells, neurons of the dentate gyrus granular layer, and neurons in the pontine nuclei. Also present in the hypothalamic nuclei, neurons in the piriform cortex, and nuclei of the brainstem (at protein level). Mainly expressed in brain and jejunum. Weakly or not expressed in heart, spleen, lung, liver, kidney and testis. Palmitoylated, palmitoylation-deficient proteins are targeted for lysosomal degradation. Belongs to the neutral sphingomyelinase family.