Properties of digestive glycosidases and peptidases and the permeability of the peritrophic membranes of Abracris flavolineata (Orthoptera : Acrididae)

In Abracris flavolineata midguts, cellulose is hydrolyzed by at least three enzymes, whereas the most active hemicellulases are a laminarinase (pH opt imum 5.7, M-r 146 k) and three lichenases (pH optima in the range 5-7.3; M- r values: 22, 71, and 97 k). Digestion of hemicellulose is completed by P-g lucosidases described elsewhere and by an alpha-mannosidase (pH optimum 3.7 , K-m 1.7 mM). There are a major and two minor amylases (pH optimum 6.5; M- r values: 42, 45, and 108 k) activated by chloride. Two of the cl-glucosida ses (M-r, 74 and 94 k) are active on maltose and hence should finish the di gestion of starch. It is not clear what is the natural substrate of the rem aining a-glucosidase (M-r 93 k). The major a-galactosidase (M-r 112 k) is a ctive on melibiose and raffinose, whereas the minor (M-r 70k) may be active on digalactosyl diglycerides. The effect of pH on azocasein hydrolysis and electrophoresis data suggest that trypsin is a major and chymotrypsin and cysteine proteinase are minor enzymes. The cysteine proteinase may derive f rom the leaves ingested by the grasshopper, laking into account its activit y in leaves. Protein digestion is finished by two soluble aminopeptidases ( M-r 92 and 105 k), a major membrane-bound aminopeptidase (M-r 97 k) and two membrane-bound dipeptidases (M-r 87 k). The sizes of the digestive enzymes recovered in A. flavolineata crops suggest that the pores of the semi-flui d caecal peritrophic membrane have diameters larger than 8.6 nm. (C) 1999 E lsevier Science Inc. All rights reserved.