Isolation, Purification, and Characterization of the Oligomeric Seed Globulin from Amaranthus hypochondriacus

Abstract

The main storage seed protein of Amaranthus hypochondriacus, the oligomeric salt-soluble globulin, was isolated and purified to homogeneity by Sephacryl S-300 gel filtration and Separon Hema-Bio 1000 DEAE anion-exchange chromatography. The globulin had two heterogeneous forms, a major and minor species with apparent molecular masses of 398, 000 and 337, 000 daltons, respectively. Each of the two species were analyzed by sodium-dodecyl-sulfate polyacrylamide gel electrophoresis (PAGE) and by native-PAGE (without prior reduction of disulfide bonds). Only slight differences were observed in their subunit patterns although appreciable differences in mobility and dissociation behaviour were noted on native-PAGE. The major protein fraction was oligomeric, consisting of a tetrameric and hexameric moiety held together by weak secondary forces. The minor fraction, a hexamer of slightly higher apparent molecular mass was a polymeric species derived in part from a sulfhydryl-disulfide interchange reaction.