Immunological studies on lysosomal sphingomyelinase: identification of a 28 000-Da component deficient in urine from patients with Niemann-Pick disease types A and B.

The immunoblotting technique was used to identify sphingomyelinase protein in samples of tissue and urine after subjection to polyacrylamide-gel electrophoresis in the presence of sodium dodecyl sulphate. In a sphingomyelinase preparation purified from control urine a prominent band was seen with an Mr of 28 000 Da. Glycoprotein fractions from urine and placenta, a membrane extract from spleen, and a partially purified sphingomyelinase preparation from placenta contained the 28 000-Da band plus additional, higher-Mr bands. The 28 000-Da band was detectable in urine from a patient with Niemann-Pick disease type C, but not in urine from patients with Niemann-Pick disease types A and B. It is concluded that sphingomyelinase is composed of at least one polypeptide with an Mr of 28 000 Da and that this polypeptide is deficient in the urine of patients with Niemann-Pick disease types A and B.