To define the biochemical mechanisms underlying secretion in the exocrine pancrease, we propose the following: A. To characterize zymogen granule polypeptides from dog and rat pancreas. Purified granule membrane glycoproteins will be characterized in terms of amino acid and carbohydrate compositions, and glycopeptide linkage. The relative carbohydrate compositions of secretory products will be assessed by isopycnic centrifugation. B. Topology of zumogen granules. Membrane proteins on the outer (cytoplasmic) granule membrane surface will be distinguished using selective labeling procedures. C. Reaggregation of zymogen granule membranes. Vesicle formation from granule membrane components dissolved in detergent will be assessed. D. Subcellular distribution of glycoproteins and glycosyltransferases. The distribution of membrane glycoproteins will be assessed by SDS- polyacrylamide gel electrophoresis. The location of galactosyltransferase and sialytransferase will be studied. E. Role of zymogen granule membrane in exocytosis. The binding of granule membrane polypeptides to isolated plasma membranes will be examined. F. Kinetics of glycoprotein synthesis. In vitro pulse-chase experiments will be employed to establish the temporal sequence in translation and glycosylation.