Influence of the Extracting Solvent upon the Structural Properties of Amaranth (Amaranthus hypochondriacus) Glutelin

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Abstract
Two amaranth glutelin preparations, Gt-bo extracted with borate buffer at pH 10 and Gt-na extracted with 0.1 N NaOH, were characterized and compared with the amaranth polymerized 11S globulin (Gp, globulin-P). Gt-bo and Gt-na presented very similar polypeptidic composition and a similar reactivity against an anti-Gp polyclonal antibody, although lower than that of Gp. It is demonstrated that Gt-na is composed of denatured and dissociated molecules, whereas Gt-bo consists of folded molecules. The size, polypeptidic composition, thermal stability, and denaturation enthalpy of Gt-bo molecules were similar to those of Gp subjected to a borate treatment at pH 10. The Gp immunoreactivity decreased to the level of Gt reactivity when subjected to alkaline treatment; this could be due to conformational changes. Results suggest that, like Gp, amaranth Gt molecules may be hexameric oligomers of approximately 300 kDa. They would be partially unfolded during the alkaline extraction. Keywords: Amaranth; glutelin; protein structure; storage protein