Purification and characterization of two α-amylase inhibitors from seeds of tepary bean ( Phaseolus acutifolius A. Gray)

Two proteinaceous α-amylase inhibitors termed αAI-Pa1 and αAI-Pa2 were purified from seeds of Phaseolus acutifolius. αAI-Pa2 resembles two well-known common bean inhibitors, whereas αAI-Pa1 is composed of a single glycopolypeptide, and its N-terminal amino acid sequence resembles that of seed lectins in the tepary bean and common bean. Two proteinaceous α-amylase inhibitors termed αAI-Pa1 and αAI-Pa2 were purified from seeds of a cultivated tepary bean ( Phaseolus acutifolius A. Gray, cv. PI311897). The two inhibitors differed in their specificity towards α-amylases of insect pests such as bruchids, although neither showed any inhibitory activity against α-amylases of mammalian, bacterial or fungal origin. αAI-Pa2 resembles two common bean inhibitors, αAI-1 and αAI-2, in several characteristics such as N-terminal amino acid sequences and oligomeric structure being composed of α and β subunits. In contrast αAI-Pa1 is composed of a single glycopolypeptide with a molecular mass of 35 kDa, and its N-terminal amino acid sequence resembled that of seed lectins in tepary bean and common bean. The information on the two tepary bean α-amylase inhibitors may be useful not only for providing insight into critical structure for the specificity towards different α-amylase enzymes but also for enhancing insect resistance in crops.