TRYPSIN SECRETION IN MUSCA-DOMESTICA LARVAL MIDGUTS - A BIOCHEMICAL AND IMMUNOCYTOCHEMICAL STUDY

Musca domestica larvae have trypsin in their midgut cells and contents , mainly at the posterior region, Both soluble and membrane-bound form s of trypsin are found, Membrane-bound trypsin is not affected by papa in or phosphatidylinositol-specific phospholipase C, although it is so lubilized with equal efficiency by detergents with high and low critic al micellar concentrations, The solubilization increases at high pH va lues in the presence or absence of detergent, Once solubilized, membra ne-bound trypsin behaves as a hydrophilic protein, M. domestica trypsi n was purified to homogeneity and used to raise antibodies in a rabbit . A Western blot of M. domestica membrane-bound and soluble midgut pro teins, after sodium dodecyl sulfate-polyacrylamide gel electrophoresis using trypsin antiserum, showed only bands co-migrating with trypsin, With this antiserum, trypsin was immunolocalized in the membranes of secretory and Golgi vesicles, surface of microvilli and midgut content s of M, domestica posterior midgut, The data suggest that trypsin is b ound to the secretory vesicle membrane by a hydrophobic peptide anchor . Upon exocytosis, most trypsin is solubilized apparently because the neutral pH of the luminal contents causes a conformational change whic h hinders part of the trypsin anchor, Copyright (C) 1996 Elsevier Scie nce Ltd.