Zymogen secretion and phospholipid metabolism in the pancreas. Phospholipids of the zymogen granule.

1. Acetylcholine produced a fivefold increase in the specific radioactivity of phosphatidylinositol in guinea-pig pancreas slices incubated in the presence of [(32)P]-orthophosphate, but did not affect the specific radioactivity of the terminal phosphate of ATP. 2. The secretagogues acetylcholine and pancreozymin had no direct effect on the enzymes of phosphatidylinositol biosynthesis in guinea-pig pancreas homogenates. 3. Pancreozymin in vivo increased the incorporation of [(32)P]orthophosphate into phosphatidylinositol but not into phosphatidylcholine, phosphatidylethanolamine or phosphatidylserine. 4. The zymogen-granule membrane contained no unusual phospholipids or lysophospholipids, although its high cholesterol/phospholipid ratio resembled that of plasma membrane. 5. Phospholipase A activity during fractionation sometimes produced lysophospholipids in mitochondrial, microsomal and zymogen-granule fractions.