Sphingomyelin phosphodiesterase or simply Sphingomyelinase (SMase) is a hydrolase enzyme that is involved in sphingolipid metabolism reactions. SMase is a member of the DNase I superfamily of enzymes and is responsible for breaking sphingomyelin (SM) down into phosphocholine and ceramide. The activation of SMase has been suggested as a major route for the production of ceramide in response to cellular stresses.

Alk-Smase Converts sphingomyelin to ceramide. Also has phospholipase C activity toward palmitoyl lyso-phosphocholine. Does not appear to have nucleotide pyrophosphatase activity.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.