Phosphorylation of a pancreatic zymogen granule membrane protein by endogenous calcium/phospholipid-dependent protein kinase.
The occurrence of phospholipid-sensitive calcium-dependent protein kinase (referred to as C kinase) and its endogenous substrate proteins was examined in a membrane preparation from rat pancreatic zymogen granules. Using exogenous histone H1 as substrate, C kinase activity was found in the membrane fraction. The kinase was solubilized from membranes using Triton X-100 and partially purified using DEAE-cellulose chromatography. An endogenous membrane protein (Mr approximately equal to 18 000) was found to be specifically phosphorylated in the combined presence of Ca2+ and phosphatidylserine. Added diacylglycerol was effective in stimulating phosphorylation of exogenous histone by the partially purified C kinase, but had no effect upon phosphorylation of the endogenous 18 kDa protein by the membrane-associated C kinase. Phosphorylation of the 18 kDa protein was rapid (detectable within 30 s following exposure to Ca2+ and phosphatidylserine), and highly sensitive to Ca2+ (Ka = 4 microM in the presence of phosphatidylserine). These findings suggest a role for this Ca2+-dependent protein phosphorylation system in the regulation of pancreatic exocrine function.
D000818:Animals; D002118:Calcium / Q000502:physiology; D003594:Cytoplasmic Granules / Q000378:metabolism; D007425:Intracellular Membranes / Q000378:metabolism; D008297:Male; D008565:Membrane Proteins / Q000378:metabolism; D008970:Molecular Weight; D010179:Pancreas / Q000378:metabolism*; D010718:Phosphatidylserines / Q000502:physiology; D010766:Phosphorylation; D011493:Protein Kinase C; D011494:Protein Kinases / Q000378:metabolism; D051381:Rats
D008565:Membrane Proteins; D010718:Phosphatidylserines; D011494:Protein Kinases; D011493:Protein Kinase C; D002118:Calcium