Cereal Chem 68:516-521   |  VIEW ARTICLE

Alpha-Amylase Inhibitors from Rice: Fractionation and Selectivity Toward Insect, Mammalian, and Bacterial Alpha-Amylases.

G.-H. Feng, M. Chen, K. J. Kramer, and G. R. Reeck. Copyright 1991 by the American Association of Cereal Chemists, Inc. 

Rice, a cereal grain in which proteinaceous alpha-amylase inhibitors have not been well characterized, was found to contain amylase activity and numerous proteinaceous alpha-amylase inhibitors. Inhibitory activity in crude extracts was best detected after the extracts were heated to inactivate the endogenous amylase activity. A relatively simple procedure was developed to extract alpha-amylase inhibitors from rice. Rice flour was extracted with 0.15M NaCl, and the crude extract was heated at 70 C for 20 min. A portion of the heat-soluble protein was then precipitated by adding ammonium sulfate to a concentration of 1.8M. Sodium dodecyl sulfate polyacrylamide gel electrophoresis showed that the ammonium sulfate precipitate was composed of relatively small proteins with an apparent molecular mass of approximately 14 kDa. With two- dimensional gel electrophoresis, the ammonium sulfate fraction was resolved into at least eight proteins, most with pIs between 8 and 9. Further separation was done by reversed-phase high-performance liquid chromatography (RP-HPLC). More than 17 protein peaks were resolved. Individual HPLC fractions were assayed for inhibitory activities toward a group of insect (rice weevil, red flour beetle, confused flour beetle, and yellow mealworm), mammalian (human salivary and porcine pancreatic), and bacterial (Bacillus) alpha- amylases. The results showed that 13 of the HPLC fractions examined contained inhibitors of one or more of the alpha-amylases tested. Several fractions were selective toward insect alpha-amylases. Some inhibited only one of the four insect alpha-amylases, whereas others inhibited both insect and mammalian alpha- amylases. None of the fractions inhibited the bacterial alpha-amylase.