Biochemical Characterization of Rice Glutelin

The two major subunits of rice glutelin, the acidic (alpha) and basic (beta) polypeptides were purified by chromatofocusing and cation exchange chromatography, respectively. The molecular weight range of the alpha polypeptides was 28.5 to 30.8 kilodaltons and the molecular weight range of the beta polypeptides was 20.6 to 21.6 kilodaltons. Electrofocusing in polyacrylamide gels showed that the isoelectric points of the alpha and beta polypeptides were 6.5 to 7.5 and 9.4 to 10.3, respectively. At least 12 polypeptides of the alpha-group and nine polypeptides of the beta-group could be separated by electrofocusing. The amino acid compositions of whole glutelin, and the purified alpha and beta subunits were analyzed. The alpha subunit contained more glutamic acid/glutamine, serine, and glycine, and less alanine, lysine, aspartic acid/asparagine, and isoleucine than the beta subunit. A comparison of the amino acid composition of rice glutelin subunits with those of the 11S proteins from eight other plant species indicated that there is more similarity between the beta subunits than the alpha subunits of several diverse plant species.