ALPHA-GALACTOSIDASE ACTIVITY IN INGESTED SEEDS AND IN THE MIDGUT OF DYSDERCUS-PERUVIANUS (HEMIPTERA, PYRRHOCORIDAE)

The midgut of Dysdercus peruvianus is divided into three main sections (V-1-V-3) and is linked through V-4 to the hindgut. The distribution of alpha-galactosidase activity in the different gut segments of D. pe ruvianus females was studied. alpha-galactosidase hydrolyzes the trisa ccharide raffinose, the major carbohydrate of cotton seeds, on which t he insects live. In D. peruvianus midgut alpha-galactosidase activity is mainly found in soluble fractions of V-1 contents. However, a compa rison between specific activities using different alpha-galactosidase substrates in cotton seed extracts, V-1 tissue homogenate, and midgut contents suggested that the contribution of the enzymes from seeds may be very significant. Cel filtration on Sephacryl S-200 of samples fro m seed extracts, V-1 tissue, and V-1 contents revealed that in all sam ples raffinose hydrolysis is accomplished by alpha-galactosidases with similar M(r) (30,000 +/- 3,000) and dogs not involve the activity of a beta-fructosidase. Thermal inactivation studies of extracts from the three sources suggested that there was only one molecular form of the insect alpha-galactosidase and that the activity found in V-1 content s includes enzymes derived from the seed kernel. In insects fed with c otton seeds, the alpha-galactosidase activity increased in parallel wi th diet ingestion. In starved insects fed with tablets of sucrose plus raffinose, an increase in alpha-galactosidase activity was also obser ved, confirming that the insect is able to synthesize part of the gut enzyme. The results indicated that raffinose digestion starts in V-1 u tilizing alpha-galactosidases derived from the seed kernel and by an a dditional alpha-galactosidase synthesized by insect tissues. The actio n of alpha-galactosidases liberates galactose and sucrose, which are s equentially hydrolyzed by the major membrane-bound alpha-glucosidase r eleasing glucose and fructose in V-1 and V-2 lumina. (C) 1997 Wiley-Li ss, Inc.