Responsible for the hydrolysis of the phosphosphingolipids (IPS), inositol phosphorylceramide (IPC), mannosylinositol phosphorylceramide (MIPC), and mannosyldiinositol phosphorylceramide (M(IP)2C) (PubMed:11006294). Regulates sphingolipid metabolism in mitochondria, especially the formation of alpha-hydroxylated very long chain phytoceramides. The generated ceramides contribute to the normal function of mitochondria (PubMed:17880915). Also active on sphingomyelin (SM), but this activity is probably not physiologically relevant (PubMed:11006294). an N-acyl-(4R)-4-hydroxysphinganine-1-phosphoinositol + H2O = 1D-myo-inositol 1-phosphate + an N-acyl-(4R)-4-hydroxysphinganine + H(+) a mannosylinositol-1-phospho-N-acyl-sphingoid base + H2O = an N-acyl-sphingoid base + H(+) + mannosylinositol-1-phosphate an inositol phosphomannosylinositol-1-phospho-N-acyl-(4R)-4-hydroxysphinganine + H2O = an N-acyl-(4R)-4-hydroxysphinganine + H(+) + mannosyldiinositol-1-phosphate Activated through localization to mitochondria in specific growth phases. Lipid metabolism; sphingolipid metabolism. Localization is regulated in a growth-dependent manner. Predominantly in the ER during early growth and becomes associated with mitochondria in late logarithmic growth. Eliminates endogenous IPS-PLC activities. Present with 2170 molecules/cell in log phase SD medium. Belongs to the neutral sphingomyelinase family.