The peritrophic membrane (PM) is a film-like structure that separates food from midgut tissue, composed of chitin and proteins. It protects the epithelium against food abrasion and microrganisms and has other functions based on compartimentalization of enzymes. Amongst these are increasing digestive efficiency and decreasing enzyme excretion.
Endopeptidase activity was followed in PM contents contained in bags being dialysed. Control samples were dialysed only after incubation. In experimental conditions the activity was 60% higher than in control conditions. This may be due to the removal of small peptides formed by the endopeptidases and that could inhibit them. Similar phenomena may take place in insect midgut, since the presence of a PM plus the countercurrent fluid flux can act as a dialysis tube.
Midgut content of Spodoptera frugiperda, Tenebrio molitor and Musca domestica larvae was divided into several parts (8-9) and activities of trypsin, chymotrypsin and amylase were determined in them. The results showed that there are different patterns of enzyme gradients along the midgut, depending on the midgut sites of water absortion and secretion and enzyme secretion. These gradients are thought to depend on PM.
S. frugiperda larvae lose the luminal enzyme gradient when PM is completely disrupted by feeding the insect for 8 hours with a calcofluor-containing diet. Accordingly, the enzyme excretion rate increases when larvae have their PM disrupted by calcofluor at anterior midgut. The results are in accordance with the proposal that PM favors the decrease of enzyme excretion by permiting enzyme recycling.Supported by FAPESP, CNPq and PRONEX.
Species 1: Lepidoptera Noctuidae Spodoptera frugiperda (fall armyworm)
Species 2: Coleoptera Tenebrionidae Tenebrio molitor (yellow mealworm)
Species 3: Diptera Muscidae Musca domestica (house fly)
Keywords: enzyme excretion, enzyme recycling
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