Deficiency of taurocholate-dependent phospholipase C acting on phosphatidylcholine in Niemann-Pick disease

Examination of release of labeled glyceride from 2-1-¹⁴C]oleoyl phosphatidylcholine by a soluble extract of human fibroblasts confirmed the presence of phosphodiesterase which is stimulated strongly by sodium taurocholate. This activity was maximal at pH 4.5 and was inhibited by sphingomyelin and 5′ AMP. Assay of the phosphatidycholine phosphodiesterase activity in fibroblast cultures from patients with Niemann-Pick disease revealed a severe deficiency in those cultures also deficient in sphingomyelinase (3 type A and 4 type B) whereas assay of cultures from Niemann-Pick patients without sphingomyelinase deficiency (3 type C and 1 with neurovisceral lipidosis and vertical supranuclear ophthalmoplegia) gave activities similar to controls. The distribution of label in the products of the reactions catalyzed by both control and Niemann-Pick extracts indicates that the phosphodiesterase activity observed was phospholipase C and that phospholipase D was not involved. The close correlation of phosphatidylcholine phospholipase C and sphingomyelinase activities in the control and mutant fibroblasts strongly suggests that both activities are catalyzed by one enzyme. Various alterations in the regulation of the specificity of a multifunctional phospholipase C may underlie phenotypic variation in Niemann-Pick disease.