α-Amylase Inhibitor

Abstract

α-Amylase inhibitors are heat-labile proteins that are active against salivary, pancreatic, bacterial, or insect α-amylases. Two thirds of the albumin fractions of wheat are composed of multiple protein components capable of inhibiting α-amylases of diverse origin. Three major groups of α-amylase have been characterized, based on molecular weight: 60,000, 24,000, and 12,500 Da. The inhibitor forms a complex with amylase. The complex formation can inactivate the amylase and in turn cause reduction in starch digestion. The fact that the wheat amylase inhibitors are highly effective toward insect amylases suggests that they are part of a defense mechanism of the seed against insect attack, and as far as animal nutrition is concerned, they decrease the availability of starch. On the other hand, in human subjects it was also demonstrated that the wheat amylase inhibitors could reduce hyperglycemia and hyperinsulinemia in diabetic patients. The purifi ed inhibitors extracted from the beans are a glycoprotein (10% carbohydrate) with a molecular weight of 40,000 to 50,000 Da, 1 mol of which reacts with pancreatic amylase to form a 1: 1 complex. The detection of starch in the feces of rats fed diets containing raw beans with high antiamylase activity suggests that this factor may be active in vivo. Extracts from Leoti sorghum grain have been reported to be active against salivary and pancreatic amylases, implying that they inhibit dietary starch digestion in the gastrointestinal tract. Administration of amylase inhibitors to chickens depressed growth and caused pancreatic hypertrophy.