Fractionation of alcohol-soluble reduced corn glutelins on phosphocellulose and partial characterization of two proline-rich fractions

Alcohol-soluble reduced glutelin (ASG) from corn endosperm was fractionated by ion exchange chromatography on phosphocellulose. The ASG was dissolved in 0.01M sodiumlactate buffer (pH 3.8) containing 60% isopropanol and 0.05M 2-mercapto- ethanol and loaded onto phosphocellulose columns equilibrated with the same buffer. Columns were developed with a linear 0.0-0.5M NaCl gradient formed in the starting buffer, yielding 2 major overlapping peaks (each with shoulders) and 4 minor peaks. Each peak and subpeak was analysed by sodium dodecyl sulphate-polyacrylamide gel electrophoresis and by isoelectric focusing. Five fractions contained essentially a single size component. The 2 late-eluting fractions were further characterized. Each had the same mol. wt. (27 500) and was heterogeneous when analysed by isoelectric focusing. These fractions were partially soluble in water, rich in proline (26%) and glutamic acid (16%), and deficient in lysine (0.1%) and had threonine as the NH2-terminal residue. Polypeptides in these 2 fractions were similar in physicochemical characteristics to water-soluble ASG, and appeared to be coded by homologous genes.