Abstract
Niemann-Pick disease exists in multiple forms. Two types (A and B) are characterized by sphingomyelin storage and markedly reduced levels of sphingomyelinase activity. A third form (Type C) also shows sphingomyelin storage but total enzyme activity is within normal limits. Since defects in multiple enzyme species could explain this data, extracts of human liver were subjected to isoelectric focusing in sucrose gradients (pH range 4-7). Two major (I and II) and two minor (III and IV) species of sphingomyelinase were resolved in normal liver. Recovery of enzyme activity was 70-80%. Isoenzyme I has a pI of 4.5-4.7, a pH optimum near 5.0 and a Km of 0.069 mM. The second major species (II) has a pI of 5.1-5.3, a pH optimum near 4.0 and a Km of 0.045 mM at pH 4.0. Both species are found at the corresponding isoelectric point when re-focused separately. Species III and IV have not been characterized. In liver from a known case of Niemann-Pick Type C, only one major isoenzyme (pI 4.6) was found. It re-focused to the same isoelectric point and showed the same properties as isoenzyme I from normal liver. In preliminary experiments on brain, isoenzyme I was the major species present. We conclude that multiple species of sphingomyelinase exist in human tissues and the absence of species II in liver constitutes the genetic defect in Type C, Niemann-Pick disease. Supported by Provincial Health Grant PR 360C.
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Callahan, J., Khalil, M. & Lowden, J. NIEMANN-PICK DISEASE, TYPE C: ABSENCE OF A SPHINGOMYELINASE ISOENZYME. Pediatr Res 8, 387 (1974). https://doi.org/10.1203/00006450-197404000-00285
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DOI: https://doi.org/10.1203/00006450-197404000-00285