Biosynthesis of the major glycoprotein associated with zymogen-granule membranes in the pancreas.
The biosynthesis of GP-2, the major glycoprotein associated with zymogen-granule membranes in the pancreas, was studied in acinar cell suspensions from rat pancreas. Pulse-chase experiments, using [35S]methionine, were performed and the processing of GP-2 was analyzed by immunoprecipitation and sodium dodecyl sulfate/polyacrylamide gel electrophoresis. GP-2 is synthesized as a precursor glycoprotein with apparent molecular weight Mr = 73000. Within 60 min after synthesis it is almost completely converted to the mature form (Mr = 78000-80000). Only the precursor form of GP-2 is sensitive to digestion with the glycosidase endo-beta-N-acetylglucosaminidase H, indicating that the observed conversion reflects the processing of 'high-mannose' oligosaccharides into complex type oligosaccharides. Acinar cells cultured in the presence of increasing concentrations of the N-glycosylation inhibitor tunicamycin synthesize 5-6 distinct precursor GP-2 species with apparent molecular weights decreasing from 73000-61000. We conclude that GP-2 contains five or six N-linked carbohydrate chains. From cell fractionation studies it was established that the precursor GP-2 is present in a microsomal fraction with high density (greater than 1.169 g/ml) presumably derived from the rough endoplasmic reticulum; mature GP-2 is localized in low density microsomes (less than 1.130 g/ml) probably Golgi vesicles. The GP-2 in zymogen granule membranes is also in the mature form.
D000818:Animals; D001692:Biological Transport; D003594:Cytoplasmic Granules / Q000378:metabolism*; D004591:Electrophoresis, Polyacrylamide Gel; D004721:Endoplasmic Reticulum / Q000378:metabolism; D006023:Glycoproteins / Q000096:biosynthesis*; D006056:Golgi Apparatus / Q000378:metabolism; D007106:Immune Sera / Q000032:analysis; D007120:Immunochemistry; D066298:In Vitro Techniques; D007425:Intracellular Membranes / Q000378:metabolism*; D007797:Laminin; D008297:Male; D010179:Pancreas / Q000378:metabolism*; D051381:Rats; D011919:Rats, Inbred Strains; D012967:Sodium Dodecyl Sulfate; D014415:Tunicamycin / Q000494:pharmacology
D006023:Glycoproteins; D007106:Immune Sera; D007797:Laminin; D014415:Tunicamycin; D012967:Sodium Dodecyl Sulfate