Properties and compartmentalization of digestive carbohydrases and proteases in Scaptotrigona bipunctata (Apidae: Meliponinae) larvae

Abstract - Aminopeptidase (pH optimum, pH_o, 7.5; enzyme relative molecular weights, M_r values: 1, 110 000; 2, 190 000; 3, 300 000), amylase (pH_o 5.5, M_r values: 1, 21 000; 2, 68 000); cellobiase (pH_o 5.5) and maltase (pH_o 5.0, M_r values: 1, 75 000; 2, 110 000; 3, 200 000) are found in the anterior (60-80%) and posterior (20-35%) midgut contents, with minor amounts occurring in midgut cells (2-5%). Trypsin (pH_o 7.0, M_r 38 000) occurs mainly in the posterior (62%) rather than in the anterior (37%) midgut contents. Maltase 1 is more active on sucrose than on maltose, the reverse being true for the other maltases. A cysteine-proteinase (pH_o 5.6, M_r 79 000) was found in major amounts in the pollen grains ingested by the larvae. The results suggest that, except for a cysteine-proteinase derived from ingested pollen, all digestive enzymes originate in the midgut tissue and are most active in the luminal contents. Evidence is presented supporting the hypothesis that enzymes and nutrients diffusing through the peritrophic membrane are translocated forward by a countercurrent flux. The absence of a midgut differentiation of midgut luminal pH in S bipunctata larvae is though to be derived from putative Hymenopteran ancestors.