AN IMMUNOCYTOCHEMICAL INVESTIGATION OF TRYPSIN SECRETION IN THE MIDGUT OF THE STABLEFLY, STOMOXYS-CALCITRANS

Musca domestica trypsin antibody cross-reacts with polypeptide bands o f M(r) 25,000 and 30,000 showing proteolytic activity from Stomoxys ca lcitrans midgut extracts, Secretory granules from the main enzyme-secr eting region, the opaque zone, stained heavily with the trypsin antibo dy in both unfed and blood-fed flies, Heterogeneous staining of granul es suggests the unequal distribution of trypsin in secretory granules, This is also consistent with the occurrence of non-parallel secretion , which is also suggested by the possible preferential release of smal ler, heavily stained secretory granules in fed flies, The predigestive , anterior midgut region responsible for rapid dehydration of the bloo d meal, the reservoir zone, contains a different population of secreto ry granules which stain heavily with trypsin antibody. This zone conta ins 20% of the midgut trypsin activity in unfed flies; trypsins are he ld here as proenzymes which are probably only activated postsecretion, In the midgut lumen of both unfed and blood-fed flies, trypsin is mai nly immunolocalized in the ectoperitrophic space. Enzyme assays sugges t that 5-15% of the lumenal trypsin is associated with the peritrophic matrix, The finding of intact secretory granules plus cell debris in the ectoperitrophic space of opaque and lipoid zones of blood-fed flie s supports the contention that some trypsin is released by apocrine se cretion in this insect. Copyright (C) 1996 Elsevier Science Ltd.