Purification and characterization of a glycoprotein alpha-amylase inhibitor from tepary bean seeds (Phaseolus acutifolius A Gray)

An alpha-amylase inhibitor was extracted and purified from tepary bean seeds. It is a 37,700 u (Da) glycoprotein determined by electrophoresis. The carbohydrate moiety (17%), determined by gas chromatography-mass spectrometry, consisted mainly of glucose and mannose, with small quantities of 2-acetamide-2-deoxy-glucose, acetyl-xylose, and xylose. This inhibitor is similar in several characteristics to previous alpha-amylase inhibitors studied in other bean seeds, including its molecular mass and its isoelectric point (4.7). The specificity toward different insect amylases was particulary high for the amylases from two bruchids, which are important pests to common beans (Z. subfasciatus and C. maculatus). This provides an interesting possibility for increasing resistance in common beans to attack by these pests. Its thermal stability uas low even at temperatures as low as 60 degrees C.