Role of midgut peritrophic membranes in regulating digestive protease activities

The peritrophic membrane (PM) is a non-cellular anatomical structure lining the midgut in most insect species. PMs perform important physiological functions, including facilitating the food digestion process and regulating digestive enzyme activities. In this study, the role of PMs in regulating digestive protease activities was examined by alteration of the PM in Trichoplusia ni larvae via experimental treatments and analyses of midgut protease activities (particularly serine proteinase activities) in the larvae with altered PMs. Protease activities were present in the PM, although to a much less extent as in the gut juice, and the association of protease activities with the PM appeared to rely on specific PM proteins. Partial removal of proteins from the PM or complete inhibition of PM formation resulted in reduction of protease activities in the midgut of treated larvae. In addition to quantitative reduction of protease activities, a change of protease zymography profile was also observed in the midgut of larvae treated with a mucin specific metalloprotease, the enhancin from Trichoplusia ni granulovirus.