SUBUNIT STRUCTURES AND ESSENTIAL AMINO ACID RESIDUES OF WHITE KIDNEY BEAN (PHASEOLUS VULGARIS) ?-AMYLASE INHIBITORS

The nutraceutical role of thePhaseolus vulgarisα-amylase inhibitor

The present review assesses the potential of thePhaseolus vulgarisα-amylase inhibitor isoform 1 (α-AI1) starch blockers as a widely used remedy against obesity and diabetes. Consumption of the α-amylase inhibitor causes marginal intraluminal α-amylase activity facilitated by the inhibitor's appropriate structural, physico-chemical and functional properties. As a result there is decreased postprandial plasma hyperglycaemia and insulin levels, increased resistance of starch to digestion and increased activity of colorectal bacteria. The efficacy and safety of the amylase inhibitor extracts, however, depend on the processing and extraction techniques used. The extracts are potential ingredients in foods for increased carbohydrate tolerance in diabetics, decreased energy intake for reducing obesity and for increased resistant starch. Research developments in the distribution and biosynthesis of the α-amylase inhibitor, relevant physico-chemical properties, the molecular starch-blocking mechanism, anti-obesity and anti-diabetes effects, safety of extracts and the need for research into their potential anti-colorectal cancer effect are discussed.

Bean alpha-amylase inhibitor 1 in transgenic peas (Pisum sativum) provides complete protection from pea weevil (Bruchus pisorum) under field conditions

Two alpha-amylase inhibitors, called alphaAI-1 and alphaAI-2, that share 78% amino acid sequence identity and have a differential specificity toward mammalian and insect alpha-amylases are present in different accessions of the common bean (Phaseolus vulgaris). Using greenhouse-grown transgenic peas (Pisum sativum), we have shown previously that expression of alphaAI-1 in pea seeds can provide complete protection against the pea weevil (Bruchus pisorum). Here, we report that alphaAI-1 also protects peas from the weevil under field conditions. The high degree of protection is explained by our finding that alphaAI-1 inhibits pea bruchid alpha-amylase by 80% over a broad pH range (pH 4.5-6.5). alphaAI-2, on the other hand, is a much less effective inhibitor of pea bruchid alpha-amylase, inhibiting the enzyme by only 40%, and only in the pH 4.0-4.5 range. Nevertheless, this inhibitor was still partially effective in protecting field-grown transgenic peas against pea weevils. The primary effect of alphaAI-2 appeared to be a delay in the maturation of the larvae. This contrasts with the effect of alphaAI-1, which results in larval mortality at the first or second instar. These results are discussed in relationship to the use of amylase inhibitors with different specificities to bring about protection of crops from their insect pests or to decrease insect pest populations below the economic injury level.