Catalyzes the hydrolysis of membrane sphingomyelin to form phosphorylcholine and ceramide (PubMed:16517606, PubMed:25180167). It has a relevant role in the homeostasis of membrane sphingolipids, thereby influencing membrane integrity, and endoplasmic reticulum organization and function (PubMed:31495489). May sensitize cells to DNA damage-induced apoptosis (PubMed:18505924). In skeletal muscle, mediates TNF-stimulated oxidant production (By similarity). a sphingomyelin + H2O = an N-acylsphing-4-enine + H(+) + phosphocholine Activated by phosphatidylserine and tumor necrosis factor (TNF). Inhibited by scyphostatin. Optimum pH is 7.0. Widely expressed, with highest levels in heart and skeletal muscle. Expressed in skeletal muscle (at protein level). Expressed in skeletal muscle but a lower levels than isoform 1 (at protein level). Expression is induced by DNA-damage and TNF. The disease is caused by variants affecting the gene represented in this entry. Truncated N-terminus. Truncated N-terminus. Truncated N-terminus. Truncated N-terminus. Truncated N-terminus.