GP-3, a newly characterized glycoprotein on the inner surface of the zymogen granule membrane, undergoes regulated secretion.
We have recently reported the cloning of the rat zymogen granule membrane glycoprotein GP-3 and the related pancreatic secretory lipase (Wishart, M. J., Andrews, P. C., Nichols, R., Blevins, G. T., Logsdon, C.D., and Williams, J. A. (1993) J. Biol. Chem. 268, 10303-10311). Specific antipeptide antibodies were generated against both GP-3 and secretory lipase and used for the biochemical and physiological characterization of GP-3. Western blotting confirmed that GP-3 was found exclusively in zymogen granule membranes and was absent from zymogen granule content which contains the majority of secretory lipase. Extraction of zymogen granule membranes with Triton X-114 showed GP-3 to be significantly more hydrophobic than lipase. The GP-3 amino acid sequence contains one potential N-linked glycosylation site at Asn-336. The loss of concanavalin A labeling after both chemical deglycosylation with trifluoromethanesulfonic acid and enzymatic deglycosylation with N-glycanase showed GP-3 to possess a small N-linked oligosaccharide side chain. Digestion of intact and permeabilized zymogen granules with the nonspecific protease Pronase localized GP-3 to the inner surface of zymogen granule membranes. Since GP-3 is resident on the inner surface of the zymogen granule membrane, it should appear on the outer cellular surface after exocytosis. Although membrane attachment of GP-3 was resistant to treatment with phosphatidylinositol-specific phospholipase C, we observed that GP-3 is released into the pancreatic juice and that secretion of GP-3 was greatly enhanced by cholecystokinin.
Wagner
A C
AC
Department of Physiology, University of Michigan, Ann Arbor 48109-0622.
Wishart
M J
MJ
Mulders
S M
SM
Blevins
P M
PM
Andrews
P C
PC
Lowe
A W
AW
Williams
J A
JA
D000818:Animals; D002766:Cholecystokinin / Q000494:pharmacology; D003594:Cytoplasmic Granules / Q000737:chemistry*; D007158:Immunologic Techniques; D007425:Intracellular Membranes / Q000378:metabolism; D008049:Lipase / Q000378:metabolism; D008297:Male; D008562:Membrane Glycoproteins / Q000737:chemistry / Q000378:metabolism*; D008970:Molecular Weight; D010189:Pancreatic Juice / Q000737:chemistry*; D043265:Phosphatidylinositol Diacylglycerol-Lyase; D054801:Phosphoinositide Phospholipase C; D010727:Phosphoric Diester Hydrolases / Q000378:metabolism; D051381:Rats; D017207:Rats, Sprague-Dawley; D012995:Solubility
D008562:Membrane Glycoproteins; C086380:glycoprotein 3, zymogen granule membrane; D002766:Cholecystokinin; D008049:Lipase; D010727:Phosphoric Diester Hydrolases; D054801:Phosphoinositide Phospholipase C; D043265:Phosphatidylinositol Diacylglycerol-Lyase