Demonstration and preliminary characterization of α-amylase in the sweetpotato whitefly, Bemisia tabaci (Aleyrodidae: Homoptera)

Abstract

An α-amylase that hydrolyzes unmodified starch or amylopectin azure was demonstrated in crude and partially purified extracts prepared from whole carcasses of sweetpotato whiteflies (SPW) ( Bemisia tabaci Genn.). All nymphal instars and adult SPW, including newly eclosed crawlers that had not yet fed on plant materials, were found to have active α-amylase. α-Amylase activity per mg protein was greatest in 1st instars and decreased with age up to the “pupal” stage, with a very slight increase in activity in adults. However, activity per individual did not differ substantially as a function of age. The α-amylase had an apparent molecular weight of about 70 kDa, an isoelectric point of 6.32 and eluted with about 250 mM NaCl from a strongly basic anion-exchange column. The enzyme activity was inhibited by EDTA and not activated by either NaCl or KNO 3. CaCl 2 strongly enhanced activity. α-Amylase activity was greatest at pH 7.0, but there was considerable activity at pHs above 7.0. The K m of the α-amylase was 1.47 Mm with p-nitrophenyl α- d-malto-heptaoside as substrate. The presence of an amylolytic enzyme in a phloem-feeding insect is unexpected and raises questions about current assumptions of feeding behavior of this species.