Biosynthesis of sphingomyelinase in normal and Niemann-Pick fibroblasts.
Deficient sphingomyelinase activity and massive storage of sphingomyelin are common to two clinically different forms of Niemann-Pick disease, called types A and B. Polyclonal antisera to human sphingomyelinase precipitated both enzyme activity and the polypeptide chain of purified placental sphingomyelinase. In normal fibroblasts, following a 19-h labelling period with [35S]methionine and immunoprecipitation of the labelled proteins, sphingomyelinase occurred as a single polypeptide with a mean molecular mass of 110 kilodaltons (kDa). Niemann-Pick disease type A and B fibroblasts also synthesized a sphingomyelinase polypeptide having the same molecular mass as that found in normal fibroblasts. In I-cell disease fibroblasts, a reduced amount of cross-reacting material was detected, suggesting that sphingomyelinase may be targeted to the lysosome via the phosphomannosyl receptor. Pulse-chase experiments demonstrated sphingomyelinase processing, as judged by a substantial loss of radiolabel and the appearance of an 84-kDa intermediate form of the enzyme. These results confirm and extend previous work based on autopsy specimens and urine, and show that Niemann-Pick disease fibroblasts synthesize a sphingomyelinase polypeptide. We show for the first time that an 84-kDa processed form of the enzyme is biosynthetically related to the 110-kDa polypeptide.
Jobb
E A
EA
Research Institute, Hospital for Sick Children, Toronto, Ont., Canada.
Callahan
J W
JW
D002460:Cell Line; D004591:Electrophoresis, Polyacrylamide Gel; D005347:Fibroblasts / Q000201:enzymology; D006801:Humans; D008970:Molecular Weight; D009542:Niemann-Pick Diseases / Q000201:enzymology*; D010727:Phosphoric Diester Hydrolases / Q000096:biosynthesis*; D011233:Precipitin Tests; D011499:Protein Processing, Post-Translational; D012685:Sepharose / Q000031:analogs & derivatives; D013108:Sphingomyelin Phosphodiesterase / Q000096:biosynthesis*
C028326:concanavalin A-sepharose; D012685:Sepharose; D010727:Phosphoric Diester Hydrolases; D013108:Sphingomyelin Phosphodiesterase