Prey digestion in the midgut of the predatory bug Podisus nigrispinus (Hemiptera: Pentatomidae)

[Display omitted] ► The most active salivary proteinase of Podisus nigrispinus is a collagenase. ► Once the collagenase is injected it disrupts the prey tissues that are found inside predator midgut. ► Cathepsins, amylase, aminopeptidase and α-glucosidase were isolated and characterized. ► The midgut digestive enzymes are involved in digesting the pre-orally disrupted prey tissues. ► Carbohydrate is digested in anterior and protein in middle and posterior midgut, respectively. Pre-oral digestion is described as the liquefaction of the solid tissues of the prey by secretions of the predator. It is uncertain if pre-oral digestion means pre-oral dispersion of food or true digestion in the sense of the stepwise bond breaking of food polymers to release monomers to be absorbed. Collagenase is the only salivary proteinase, which activity is significant (10%) in relation to Podisus nigrispinus midgut activities. This suggests that pre-oral digestion in P. nigrispinus consists in prey tissue dispersion. This was confirmed by the finding of prey muscles fibers inside P. nigrispinus midguts. Soluble midgut hydrolases from P. nigrispinus were partially purified by ion-exchange chromatography, followed by gel filtration. Two cathepsin L-like proteinases (CAL1 and CAL2) were isolated with the properties: CAL1 (14.7kDa, pH optimum (pHo) 5.5, km with carbobenzoxy-Phe-Arg-methylcoumarin, Z-FR-MCA, 32μM); CAL2 (17kDa, pHo 5.5, km 11μM Z-FR-MCA). Only a single molecular species was found for the other enzymes with the following properties are: amylase (43kDa, pHo 5.5, km 0.1% starch), aminopeptidase (125kDa, pHo 5.5, km 0.11mM l-Leucine-p-nitroanilide), α-glucosidase (90kDa, pHo 5.0, km 5mM with p-nitrophenyl α-d-glucoside). CAL molecular masses are probably underestimated due to interaction with the column. Taking into account the distribution of hydrolases along P. nigrispinus midguts, carbohydrate digestion takes place mainly at the anterior midgut, whereas protein digestion occurs mostly in middle and posterior midgut, as previously described in seed- sucker and blood-feeder hemipterans.