title: Isolation and characterization of the subunits of Phaseolus vulgaris alpha-amylase inhibitor.
abstract: An alpha-amylase inhibitor (PHA-I) of the white kidney bean (Phaseolus vulgaris) was found to be composed of two kinds of subunits and they were isolated on a size-exclusion column by HPLC under denaturing conditions. The alpha-subunit was free from tryptophan and cysteine and the beta-subunit contained no methionine or cysteine. There was no marked resemblance in tryptic peptide map between these subunit polypeptides. The alpha-subunit contained 28% by weight of carbohydrate, mainly made up of high mannose-type oligosacharides, whereas the sugar moiety of the beta-subunit amounted to 7% by weight and seemed to be predominantly composed of xylomannose-type oligosaccharides. By SDS-PAGE following deglycosylation, the molecular weights of the polypeptides of alpha- and beta-subunits were shown to be 7,800 and 14,000, respectively. These values were consistent with molecular sizes obtained for alpha- and beta-subunits by gel permeation HPLC in 6 M guanidine hydrochloride. The molecular weight of the native PHA-I, 28,800, obtained by gel permeation HPLC under non-denaturing conditions, suggested a heterodimeric structure for PHA-I.
authors.affiliation: Department of Agricultural Chemistry, College of Agriculture, University of Osaka Prefecture.
authors.forename: H
authors.initials: H
authors.lastname: Yamaguchi
mesh_terms: D000595:Amino Acid Sequence; D002851:Chromatography, High Pressure Liquid; D004591:Electrophoresis, Polyacrylamide Gel; D007887:Fabaceae / Q000737:chemistry*; D006031:Glycosylation; D008969:Molecular Sequence Data; D008970:Molecular Weight; D009844:Oligosaccharides / Q000737:chemistry; D010449:Peptide Mapping; D010940:Plant Proteins / Q000737:chemistry* / Q000302:isolation & purification / Q000494:pharmacology; D010946:Plants, Medicinal; D000516:alpha-Amylases / Q000037:antagonists & inhibitors*
chemical_list: D009844:Oligosaccharides; D010940:Plant Proteins; D000516:alpha-Amylases