Lowell E. Hokin

Isolation of the zymogen granules of dog pancreas and a study of their properties

Abstract The zymogen granules have been isolated from dog pancreas in relatively pure form. They contain very small amounts of ribonucleic acid and phospholipid. On a nitrogen basis they contain 2–2.5 times as much amylase and lipase and 700 to 1700 times as much protease as the whole cell. The disproportionately high protease activity in the zymogen granules is probably due to the presence of trypsin inhibitor in the whole homogenate, but not in the purified zymogen granules. The zymogen granules are stable in isotonic sucrose for long periods at pHs ranging from 5.0 to 6.0, but they are rapidly solubilized if the pH is raised to 7.2 or higher. Solubilization occurs on the acid side of pH 5.0, but is less sharp than solubilization with alkali. Suspension of the granules in water liberates about 95% of the amylase into solution, but most of the lipase and protease remain bound to the insoluble material. Since pancreatic juice is alkaline the solubilization of the zymogen granules at higher pHs can explain how they are dissolved in the pancreatic juice.

Na,K-ATPase expression in the developing brine shrimp Artemia. Immunochemical localization of the alpha- and beta-subunits.

Developing brine shrimp are a good experimental model for study of gene expression during development. Development is initiated on suspension of brine shrimp cysts in seawater. Only 48 hr are required for progression from cyst to the larval stage. We have localize the alpha- and beta-subunits in different cells by immunostaining as development progresses. Both alpha- and beta-subunits are first detected in epidermal cells in the trunk region at the emergence 2 stage (16-hr incubation). At the nauplius 1 stage (24 hr) the enzyme appears in the brain and epidermal regions, as well as in mesenchymal cells, with weaker staining in the salt gland. After further development (nauplius 2 stage, 36 hr) stronger staining appears in the salt gland and in the epidermal region. At the nauplius 3 stage (48 hr) the enzyme appears in the midgut mucosa. Co-localization of the alpha- and beta-subunits appears in all positive cells during development. In the epidermal and salt gland cells the enzyme is mainly localized on the basolateral membrane. The basolateral localization of the Na,K-ATPase in epidermal and salt gland cells suggests that Na+ is actively transported into the epidermal and salt gland cells and passively diffuses out from the apical region.

Biochemical Aspects of Excitation of Protein Secretion in Pancreas

Studies over the past several years have indicated that when secretion is stimulated in a variety of endocrine and exocrine glands there is an increased incorporation of labeled precursors into certain phospholipids (see reviews [5, 6, 8–15]). The phospholipids chiefly affected are phosphatidyl inositol and phosphatidic acid, although certain of the other phosphatides may be affected in certain tissues. Kinetic studies have indicated that the phospholipid effects in different glands are probably not the same phenomenon. For example, in the salt gland the changes in phosphatidyl inositol and phosphatidic acid are quite different than in the pancreas and appear to serve different functions. The changes in the salt gland have been described elsewhere [7,14–16]. In this presentation we shall confine our discussion primarily to the changes in phospholipid metabolism on stimulating protein secretion in the pancreas.