Joseph S. Wall

Fractionation and properties of alkylated-reduced corn glutelin proteins☆

Abstract The disulfide bonds of glutelin protein from corn endosperm were cleaved to yield polypeptide chains which were subjected to physical and chemical investigations. After reduction with mercaptoethanol and alkylation with acrylonitrile of resulting sulfhydryls, about 87% of the protein was soluble in 6 M guanidine-HC1 and 47% in 0.3 M acetic acid, whereas native protein was much less soluble in both solvents. Gel filtration chromatography on different media with those solvents established that the polypeptide chains were heterogeneous in molecular weight and appeared to aggregate in the acetic acid. Fractionation of the alkylated-reduced glutelin by repeated chromatography on Sephadex G-200 in 6 M guanidine-HC1 yielded six peaks with components that differed in electrophoretic mobilities on starch gel. Direct extraction with 70% ethanol of the alkylated-reduced protein complex yielded a fraction that contained components mainly present in three of the Sephadex chromatography peaks and were similar in some properties to zeins. Molecular weight, gel electrophoretic mobilities and amino acid compositions of all of the isolated fractions indicate that glutelin consists of a series of unique proteins which form a structural matrix stabilized by disulfide bonds in mature corn endosperm.

Isolation and characterization of a methionine-rich protein from Maize Endosperm

A 17,000 mol. wt methionine-rich (met-rich) polypeptide from alcohol-soluble reduced glutelin (ASG) of maize endosperm from the hybrid WF9 × Br 38 was purified by a combination of differential solubility and ion exchange chromatography. Antiserum specific for this polypeptide was prepared against a similar fraction purified by Polyacrylamide gel electrophoresis in the presence of sodium dodecyl sulfate (SDS-PAGE) from the inbred W64A. This polypeptide (17,000 mol. wt met-rich ASG) is distinct from zein and other ASG fractions in that it contains the highest levels of methionine (10·8 mol%), glycine, alanine, tyrosine and arginine, and the lowest levels of proline, valine, isoleucine, histidine and phenylalanine among these proteins. Its N-terminal sequence, determined for 36 residues, shows numerous dipeptide (Ala-Gly and Gly-Leu) repeats and it shares no homology with either zein or proline-rich ASG fractions; this lack of homology was also indicated by results from immunological studies.

Molecular weights of wheat γ2-, β6-, α7-, α8- and α9-gliadins

Abstract The molecular weights of wheat γ 2 -, β6-, α7-, α8- and α9-gliadins were calculated with the aid of a computer technique from sedimentation equilibrium data obtained in an ultracentrifuge equipped with photoelectric scanner. The dissociative solvents, all at pH 3.1 by addition of HCl, included 3 M urea, 0.15 M KCl; 8 M urea, 0.15 M KCl and 6 M guanidine-HCl. The minimum molecular weights for γ 2 -, α7- and α9-gliadins, obtained in 6 M guanidine-HCl, were 34 600, 30 400 and 30 900, respectively. The β6- and α8-gliadins gave minimum molecular weights of 33 000 and 36 900, respectively, in 3 M urea, 0.15 M KCl.

Disulfide Bonds: Key to Wheat Protein Functionality

Disulfide bonds in wheat proteins are major factors that determine the properties of the proteins and their functionality in wheat flour. The gliadin proteins contain mostly intramolecular disulfide bonds. In contrast, the high-molecular-weight glutenins are formed by disulfide linkages of several diverse polypeptide chains which have been separated and characterized. The linkage of these proteins in a fairly linear array contributes to the unique viscoelastic properties of glutenin. The glutenin has been separated into two fractions differing in molecular weight. The amount of highest molecular weight component is correlated with the rheological behavior of the flours from different wheat varieties. Various oxidizing and reducing agents are widely used to alter the functional behavior of wheat proteins by the action on sulfhydryl and disulfide groups.