(nSMases). Of these, alkaline SMase is found in the intestinal tract and bile, and is thought to play a role in SM digestion (Duan, 2006). In contrast, acid SMase (SMPD1) comprises both a lysosomal enzyme and a secretory SMase and its mutation results in the human Niemann-Pick disease (Jenkins et al., 2009; Schuchman, 2007). The focus of this review is the group of nSMases. At present, several nSMase isoforms have been identified and suggested to play essential roles for regulating sphingolipid metabolism.
