Choline-specific phosphodiesterase that hydrolyzes sphingomyelin releasing the ceramide and phosphocholine and therefore is involved in sphingomyelin digestion, ceramide formation, and fatty acid (FA) absorption in the gastrointestinal tract (PubMed:12885774, PubMed:12671034, PubMed:15205117, PubMed:16255717, PubMed:28292932). Has also phospholipase C activity and can also cleave phosphocholine from palmitoyl lyso-phosphatidylcholine and platelet-activating factor (PAF) leading to its inactivation (PubMed:16255717, PubMed:12885774). Does not have nucleotide pyrophosphatase activity (PubMed:12885774). May promote cholesterol absorption by affecting the levels of sphingomyelin derived from either diet or endogenous sources, in the intestinal lumen (By similarity). a sphingomyelin + H2O = an N-acylsphing-4-enine + H(+) + phosphocholine 1-hexadecanoyl-sn-glycero-3-phosphocholine + H2O = 1-hexadecanoyl-sn-glycerol + H(+) + phosphocholine a 1-O-alkyl-2-acetyl-sn-glycero-3-phosphocholine + H2O = a 1-O-alkyl-2-acetyl-sn-glycerol + H(+) + phosphocholine 1-O-octadecyl-2-acetyl-sn-glycero-3-phosphocholine + H2O = 1-O-octadecyl-2-acetyl-sn-glycerol + H(+) + phosphocholine Inhibited in a dose dependent manner by ATP, imidazole, orthovanadate and zinc ion. Not inhibited by ADP, AMP and EDTA. The catalytic domain is released into the extracellular medium when cells are treated with trypsin (PubMed:15205117). Localized at the surface of the microvillar membrane in small intestine enterocytes, and in endosome-like structures situated beneath the microvillar membrane, and in Golgi complex (PubMed:12671034, PubMed:12885774). Detected in the colon (at protein level). Expressed in the duodenum, jejunum and liver and at low levels in the ileum. Expression was very low in the esophagus, stomach and colon. N-glycosylated; required for activity and transport to the plasma membrane. Decreased levels of alkaline sphingomyelin phosphodiesterase may be associated with colon cancer. Belongs to the nucleotide pyrophosphatase/phosphodiesterase family.