Molecular aspects of enzyme synthesis in the exocrine pancreas with emphasis on

Molecular aspects of enzyme synthesis in the exocrine pancreas with emphasis on

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Proceedings of the Nutrition Society (1993), 52, 301-313 301 Molecular aspects of enzyme synthesis in the exocrine pancreas with emphasis on development and nutritional regulation BY ISABELLE LE HUEROU-LURON', EVELYNE LHOSTE', CATHERINE WICKER-PLANQUART3, NADIA DAKKA3, RENE TOULLEC', TRISTAN CORRING2, PAUL GUILLOTEAUl AND ANTOINE PUIGSERVER3 'Laboratoire du Jeune Ruminant, INRA, 65 rue de Saint Brieuc, 35042 Rennes Cidex, France, 2Laboratoire d'Ecologie et de Physiologie du Sysdme Digestif CRJ, INRA, Jouy-en-Josas, France and 3Centre de Biochimie et de Biologie Moliculaire, CNRS, Marseille, France At least twenty secretory proteins are synthesized in the exocrine pancreas of higher vertebrates, most of which are essential enzymes for digestion to be carried out. Using two-dimensional polyacrylamide-gel electrophoresis in sodium dodecyl sulphate, it has been possible to identify in the rat two isozymes of amylase (EC 3.2.1.1), the main protein (20%) present in the pancreatic secretion, a single form of lipase 3.1.1.3), colipase, phospholipase A2 3.1.1.4), ribonuclease 3.1.27.5) and deoxyribo- nuclease 3.1.21. l), and several forms of proteases, including endopeptidases (serine proteases) and exopeptidases (metalloproteases). The serine protease family, which accounts for as much as 44% of the total protein synthesis, is by far the most complex and includes a cationic and three anionic forms of trypsin 3.4.21.4), as well as two or three chymotrypsins 3.4.21.1, EC 3.4.21.2) and two elastases 3.4.21.36) with a cationic and one or two anionic isozymes in each case, and several kallikrein-like proteins. All these serine proteases have comparable molecular mass values, similar structures and catalytic functions, but quite different substrate specificities. Among the metalloproteases, two isozymic forms of carboxypeptidase A 3.4.17.1) and a single form of carboxypeptidase B 3.4.17.2) have been identified. It is worth mentioning here that the zymogen of carboxypeptidase A is characterized by its ability to complex with one or two other proteins in the pancreatic acinar cell, mostly in ruminant species but also in pigs and humans. In bovine pancreatic tissue, procarboxypeptidase A mainly occurs as a ternary complex in which the zymogen itself is non-covalently associated with chymotrypsinogen C and the so-called subunit I11 which has recently been found to derive from proproteinase E via an autolytic transformation (Pascual et al. 1990). The nucleotide sequences of the cDNA clones and/or genes encoding a given pancreatic secretory enzyme in a number of mammals or encoding isozymes in a single mammalian species have shown a fairly high degree of structural similarity among the cloned messengers. The extent of similarity between bovine anionic trypsinogen mRNA, for instance, and rat anionic and rat cationic trypsinogen mRNA is 81-84 and 75% respectively, whereas the similarity in amino acid sequence between the anionic and cationic forms of bovine trypsinogen (65%) is lower than that existing between the bovine anionic protein and other mammalian anionic trypsinogens (7345% ; MacDonald et al. 1982~; Le Huerou et al.
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This note was uploaded on 07/28/2011 for the course VET 4335 taught by Professor Sakomura during the Spring '11 term at University of the South Pacific, Fiji.

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Molecular aspects of enzyme synthesis in the exocrine pancreas with emphasis on

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