IMMUNOELECTRON MICROSCOPIC LOCALIZATION OF LYSOSOMAL BETA-GALACTOSIDASE AND ITS PRECURSOR FORMS IN NORMAL AND MUTANT HUMAN-FIBROBLASTS

  • 1 March 1986
    • journal article
    • research article
    • Vol. 40  (1) , 9-15
Abstract
Immunoelectron microscopy was performed to study the biosynthesis of lysosomal .beta.-galactosidase (.beta.-gal) in normal and mutant human fibroblasts. Using polyclonal and monoclonal antibodies we show in normal cells precursor forms of .beta.-gal in the rough endoplasmic reticulum (RER) and in the Golgi apparatus throughout the stack of cisternae. In the lysosomes virtually all .beta.-gal exists as a high molecular weight multimer of mature enzyme. In the autosomal recessive disease GM1-gangliosidosis caused by a .beta.-gal deficiency and in galactosialidosis, associated with a combined deficiency of lysosomal neuraminidase and .beta.-gal, precursor forms of the latter enzyme are found in RER, Golgi and some labeling is present at the cell surface. The lysosomes remain unlabeled, indicative for the absence of enzyme molecules in this organelle. In galactosialidosis fibroblasts also no mature .beta.-gal is found in the lysosomes but in these cells the presence of the monomeric form can be increased by leupeptin (inhibition of proteolysis) whereas addition of a partly purified 32 kDa "protective protein" results in the restoration of high molecular weight .beta.-gal multimers in the lysosomes.

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