Chemical fractionation and starch gel-urea electrophoretic characterization of albumins, globulins, gliadins, and glutenins in soft wheat

Abstract

The major objectives of this investigation were: to develop improved chemical fractionation methods for albumins, globulins, gliadins, and glutenins and to characterize these proteins by starch gel-urea electrophoresis. Improved methods for chemical fractionation of soft wheat proteins based on solubilities have been developed and are presented schematically. The degree of purity of protein fractions obtained at each step in the chemical fractionation procedure employing various solvent systems, i.e., water, 1.0 M NaCl, 0.1% NaCl, 70% ethanol, and 0.01 N acetic acid was determined by SGUE. The optimum experimental conditions for SGUE were found to be: starch gel (9.24% starch) with aluminum lactate buffer, ionic strength 0.1, pH 3.1, and 7 M urea; potential gradient 10 volts/cm; 3.5 mg of lyophilized protein applied to the gel. No significant differences in SGUE patterns were found with either vertical or horizontal positioning of the gel, at room temperature or 5°C. The soft wheat proteins have been resolved into more than twenty different components by SGUE. There is in the literature a wide variety of nomenclature assigned to the various components of the wheat proteins. A system of identifying the albumins, globulins, gliadins, and glutenins based on SGUE has been proposed in which the prominent component bands in each fraction are numbered. The fastest band is number 1 and the starting slot is number 20. The soft wheat proteins have been classified as G f, A f, Base, G s, A s, and S-zone. This classification is based on electrophoretic mobilities and not on chemical compositions or solubility properties. Two major bands, 7 and 9, were found in the albumin, globulin, and gliadin proteins. These two components have been designated as “Base proteins”, and other bands are referred to as “A fast” or “G slow” etc., according to their positions before or following the base-protein zone. The base proteins may be protein-protein associations involving albumins, globulins, and gliadins.