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α‐galactosidase activity in ingested seeds and in the midgut of Dysdercus peruvianus (Hemiptera: Pyrrhocoridae)
Author(s) -
Silva Carlos P.,
Terra Walter R.
Publication year - 1997
Publication title -
archives of insect biochemistry and physiology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.576
H-Index - 66
eISSN - 1520-6327
pISSN - 0739-4462
DOI - 10.1002/(sici)1520-6327(1997)34:4<443::aid-arch4>3.0.co;2-t
Subject(s) - raffinose , midgut , biology , stachyose , hindgut , melibiose , insect , biochemistry , foregut , digestion (alchemy) , enzyme , botany , sucrose , chromatography , larva , anatomy , chemistry
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 α‐galactosidase activity in the different gut segments of D. peruvianus females was studied. α‐galactosidase hydrolyzes the trisaccharide raffinose, the major carbohydrate of cotton seeds, on which the insects live. In D. peruvianus midgut, α‐galactosidase activity is mainly found in soluble fractions of V 1 contents. However, a comparison between specific activities using different α‐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. Gel filtration on Sephacryl S‐200 of samples from seed extracts, V 1 tissue, and V 1 contents revealed that in all samples raffinose hydrolysis is accomplished by α‐galactosidases with similar M r (30,000 ± 3,000) and does not involve the activity of a β‐fructosidase. Thermal inactivation studies of extracts from the three sources suggested that there was only one molecular form of the insect α‐galactosidase and that the activity found in V 1 contents includes enzymes derived from the seed kernel. In insects fed with cotton seeds, the α‐galactosidase activity increased in parallel with diet ingestion. In starved insects fed with tablets of sucrose plus raffinose, an increase in α‐galactosidase activity was also observed, confirming that the insect is able to synthesize part of the gut enzyme. The results indicated that raffinose digestion starts in V 1 utilizing α‐galactosidases derived from the seed kernel and by an additional α‐galactosidase synthesized by insect tissues. The action of α‐galactosidases liberates galactose and sucrose, which are sequentially hydrolyzed by the major membrane‐bound α‐galactosidase releasing glucose and fructose in V 1 and V 2 lumina. Arch. Insect Biochem. Physiol. 34:443–460, 1997. © 1997 Wiley‐Liss, Inc.