The major protein of pancreatic zymogen granule membranes (GP-2) is anchored via covalent bonds to phosphatidylinositol.
GP-2, the major integral protein characteristic of the pancreatic zymogen granule membrane can be released from the membrane by the action of a phosphatidylinositol specific phospholipase C (PI-PLC). In a hydrophobic/hydrophilic phase separation system using the non-ionic detergent Triton X-114, the membrane-bound form of the protein went from the detergent phase into the hydrophilic phase upon action of the phospholipase. PI-PLC solubilization of GP-2 unmasked an antigenic determinant similar to the cross-reacting determinant of the trypanosome variant surface glycoproteins. This determinant being a distinctive feature of the glycan moiety of phosphatidyl-inositol anchored membrane proteins, it established the glycosyl-phosphatidyl-inositol nature of the GP-2 membrane anchor. Since soluble GP-2 is also found in the contents of the granule and is secreted intact into the pancreatic juice, it is likely that one of the mechanisms responsible for its release could be a specific phospholipase. GP-2 is the first glycosyl-phosphatidyl-inositol-anchored protein that is integral to the membrane of an organelle and not located at the surface of the cell.
LeBel
D
D
Centre de recherche sur les mécanismes de sécrétion Faculty of Science, University of Sherbrooke, QC, Canada.
Beattie
M
M
D000818:Animals; D003594:Cytoplasmic Granules / Q000032:analysis*; D004792:Enzyme Precursors / Q000032:analysis*; D000939:Epitopes / Q000032:analysis; D007163:Immunosorbent Techniques; D008562:Membrane Glycoproteins / Q000378:metabolism*; D008566:Membranes / Q000032:analysis; D010179:Pancreas / Q000166:cytology* / Q000201:enzymology; D010716:Phosphatidylinositols / Q000378:metabolism*; D051381:Rats; D013552:Swine; D010738:Type C Phospholipases / Q000378:metabolism
D004792:Enzyme Precursors; D000939:Epitopes; D008562:Membrane Glycoproteins; D010716:Phosphatidylinositols; D010738:Type C Phospholipases