Cereal Chem 60:306 - 310. | VIEW
Aggregation of A-Gliadin: Gel Permeation Chromatography.
E. W. Cole, J. V. Torres, and D. D. Kasarda. Copyright 1983 by the American Association of Cereal Chemists, Inc.
The reversible association of the storage protein fraction A-gliadin (aggregable alpha-gliadin) from the wheat cultivar Scout 66 into microfibrillar aggregates was studied at several different pHs, ionic strengths, and temperatures by gel permeation chromatography on Sephacryl S-300. At pH 3 the A-gliadin eluted from the column in a peak corresponding to the monomeric form of the protein (molecular weight near 30 x 10(3)), whereas at pH 4 a peak corresponding to aggregated A-gliadin appeared, and at pH 5 the protein eluted mainly in the aggregated form at the excluded volume of the column, which indicated apparent molecular weights of 10(6) or greater for the aggregates. At pH 4 and pH 5, the percentage of the protein eluting in the aggregated form increased as ionic strength was increased from 0.005 to 0.01 or 0.015. Increase in temperature at pH 4 or pH 5 caused dissociation of the protein, and the aggregates showed greater stability with an increase in ionic strength at either pH. The ionic strength and temperature dependence of the aggregation indicated a major role for hydrogen bonding in stabilization of the microfibrillar aggregates; ionic interactions and hydrophobic interactions may be important, but apparently are of less importance. The pH dependence of the aggregation indicated that ionization of carboxylic side chains (and the C-terminal carboxyl group) is important for stabilization of the aggregated form, perhaps by permitting the formation of increased secondary and tertiary conformational structure in A-gliadin as the net positive charge on the protein is decreased.