Has in vitro nucleotide phosphodiesterase activity with nucleoside triphosphates, such as ATP (PubMed:25288789, PubMed:26783088). Has in vitro activity with p-nitrophenyl-TMP (PubMed:25288789). Has lower activity with nucleoside diphosphates, and no activity with nucleoside monophosphates (PubMed:25288789, PubMed:26783088). Has in vitro activity with CDP-choline, giving rise to CMP and phosphocholine. Has in vitro activity with CDP-ethanolamine (PubMed:26783088). Does not have sphingomyelin phosphodiesterase activity (PubMed:25288789, PubMed:26783088). Binds 2 Zn(2+) per subunit. Requires micromolar levels of Zn(2+) for activity (PubMed:26783088). Inhibited by millimolar levels of Zn(2+) (PubMed:25288789, PubMed:26783088). Optimum pH is 4-6. Monomer. Detected in blood serum. Detected in macrophages (at protein level). Up-regulated in macrophages in response to cholesterol accumulation. Up-regulated by cAMP. N-glycosylated. Belongs to the acid sphingomyelinase family.