title: Molecular forms of GM2-activator protein. A study on its biosynthesis in human skin fibroblasts.
abstract: The biosynthesis and secretion of lysosomal GM2-activator was studied in fibroblasts from controls and patients of GM2 gangliosidosis metabolically labelled with [3H]-leucine. Immunoprecipitation was performed with affinity-purified antibodies to human kidney GM2-activator protein. Normal fibroblasts and fibroblasts of variant B and O of GM2 gangliosidosis secrete GM2-activator protein as a 24-kDa polypeptide, which is able to stimulate degradation of ganglioside GM2 by beta-hexosaminidase A in the in vitro assay. In the presence of 10mM NH4Cl the rate of secretion is twice as high as in normal fibroblasts. Intracellularly, GM2-activator protein is represented in these cell lines by polypeptides with apparent molecular masses ranging from 21 kDa-22.5 kDa. Under the same labelling conditions, in two cell lines of patients with variant AB of infantile GM2 gangliosidosis intracellularly only traces of GM2-activator were detectable, whereas significant amounts of polypeptides with molecular masses between 25 and 26.5 kDa could be precipitated from the media of these fibroblasts.
mesh_terms: D002478:Cells, Cultured; D004705:Endocytosis; D004797:Enzyme-Linked Immunosorbent Assay; D005347:Fibroblasts / Q000378:metabolism; D049289:G(M2) Activator Protein; D005678:G(M2) Ganglioside / Q000378:metabolism*; D005732:Gangliosides / Q000378:metabolism*; D005733:Gangliosidoses / Q000378:metabolism; D006801:Humans; D007700:Kinetics; D007930:Leucine / Q000378:metabolism; D007976:Leupeptins / Q000494:pharmacology; D008247:Lysosomes / Q000378:metabolism; D010436:Pepstatins / Q000494:pharmacology; D010664:Phenylmethylsulfonyl Fluoride / Q000494:pharmacology; D014176:Protein Biosynthesis; D012867:Skin / Q000378:metabolism*; D014316:Tritium
chemical_list: D049289:G(M2) Activator Protein; D005732:Gangliosides; D007976:Leupeptins; D010436:Pepstatins; D014316:Tritium; C014195:Streptomyces pepsin inhibitor; D005678:G(M2) Ganglioside; D010664:Phenylmethylsulfonyl Fluoride; D007930:Leucine; C032854:leupeptin; C031375:pepstatin