STUDIES ON TRYPSIN INHIBITOR IN LOCAL CULTIVAR OF Dolichos biflorus L.
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Date
2012
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Abstract
ABSTRACT
Protease inhibitors present in seeds of legumes possess strong inhibitory
activity against trypsin and confer resistance against pests. Extraction of trypsin
inhibitor from seed flour of Dolichos biflorus L. was maximum in 0.1 M
phosphate buffer (pH 7.5). Trypsin inhibitor activity in developing seeds of
Dolichos biflorus L. cultivar was detected at 8 days after flowering (DAF) and it
increased with seed maturation till 60 DAF. The inhibitor activity was found to
decrease gradually throughout germination period. Crude extract from developing
seeds inhibited gut protease of Pieris brassicae and maximum inhibition was
observed in dessicated seeds. Trypsin inhibitor was partially purified to 5.02 fold
with 74.07 per cent recovery by ammonium sulfate precipitation and gel filtration
chromatography on Sephadex G-100 column. The inhibitor was found to be
thermostable and had pH optima of 7.5. It exhibited non-competitive inhibition
pattern with Ki value of 0.04 mg/ml. The inhibitor lost its activity on exposure to
varying concentrations of DTT thereby indicating the role of disulfide linkages in
maintaining its stability and three dimensional structure. Feeding bioassay
experiment using partially purified inhibitor showed a marked decline in per cent
survival of larvae with increase in inhibitor concentration. The larval growth was
retarded in treatment. This study signifies the insecticidal potential of Dolichos
biflorus L. trypsin inhibitor which might be exploited for raising transgenic
plants.