A comparative study of the enzymic activities of membrane fractions derived from guinea pig pancreatic homogenates has yielded the following results: Rough microsomal membranes (derived from the rough ER) have the reductase activities of the two microsomal electron transport systems but lack enzyme activities of Golgi-type (TPPase) and plasmalemmal-type (5'-nucleotidase, ß-leucyl naphthylamidase, Mg-ATPase). Smooth microsomal membranes (derived primarily from the Golgi complex), zymogen granule membranes, and plasmalemmal fractions possess overlapping enzyme activities of plasmalemmal type, in different relative concentrations for each fraction. In addition, the smooth microsomal membranes exhibit TPPase and ADPase activity and share with rough microsomes the reductase activities of the two electron transport chains. Taken together with recent data on the lipid composition of the same fractions (2), these results indicate that the membranes of the pancreatic exocrine cell are chemically and functionally distinct, and hence do not mix with one another during the transport of secretory products.

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