Effect of swainsonine on the processing and turnover of lysosomal beta-galactosidase and beta-glucuronidase from mouse peritoneal macrophages.
The effect of swainsonine, an inhibitor of Golgi alpha-mannosidase II and lysosomal alpha-mannosidase, on the synthesis, processing, and turnover of two glycoproteins, lysosomal beta-galactosidase and lysosomal beta-glucuronidase, has been studied in cultured mouse peritoneal macrophages. No effect of the inhibitor on the relative rates of synthesis of the precursor form of either enzyme was observed. On the other hand, carbohydrate processing of beta-galactosidase and beta-glucuronidase was markedly altered by swainsonine, consistent with a blockage by the inhibitor of the removal of the alpha-1,3- and alpha-1,6-linked mannose residues which occurs in normal processing. In homogenates of both normal and swainsonine-treated cells, the precursor forms of the enzymes were found exclusively in the light membrane fraction on Percoll gradients and the mature forms exclusively in the lysosomal fractions indicating that translocation from Golgi to lysosomes and proteolytic processing in the lysosome were not impaired by the presence of abnormal oligosaccharide side chains. There was no detectable effect of swainsonine during a 4-day chase period on the total cellular turnover of these enzymes which involves two processes, secretion and degradation. In the absence of swainsonine, secretion represented about 40% of the total turnover of beta-galactosidase and about 50% with beta-glucuronidase. The presence of swainsonine increased these proportions to about 60 and 70%, respectively.
D000470:Alkaloids / Q000494:pharmacology*; D000818:Animals; D004591:Electrophoresis, Polyacrylamide Gel; D005260:Female; D005696:Galactosidases / Q000378:metabolism*; D005966:Glucuronidase / Q000378:metabolism*; D006596:Hexosaminidases / Q000378:metabolism; D008247:Lysosomes / Q000187:drug effects / Q000201:enzymology*; D008264:Macrophages / Q000166:cytology / Q000201:enzymology*; D008715:Methionine / Q000378:metabolism; D051379:Mice; D008810:Mice, Inbred C57BL; D008970:Molecular Weight; D017026:Swainsonine; D001616:beta-Galactosidase / Q000378:metabolism*
D000470:Alkaloids; D008715:Methionine; D005696:Galactosidases; D006596:Hexosaminidases; D001616:beta-Galactosidase; D005966:Glucuronidase; D017026:Swainsonine