Characterization of polymeric proteins from vitreous and floury sorghum endosperm

Differences in protein content and composition between vitreous and floury endosperm were investigated using a number of different techniques. Differences in protein cross-linking between vitreous and floury endosperm were investigated using differential solubility, size exclusion chromatography (SEC), and analysis of sulfhydryl content and composition. Vitreous endosperm was found to have higher levels of total protein and kafirins, but floury enclosperm had a higher proportion of gamma-kafirins than the vitreous. Floury enclosperm was found to have higher levels of SDS-soluble proteins than SDS-insoluble proteins extracted using sonication than vitreous enclosperm. Conversely, vitreous enclosperm had a greater proportion of the insoluble proteins. SEC analysis of the polymeric proteins revealed that the insoluble proteins had more polymeric proteins than did the soluble proteins, indicating greater cross-linking and a larger M,, distribution. Vitreous enclosperm was also found to have a greater percentage (i.e., a higher ratio of disulfide to total sulfhydryls) of disulficle bonds than floury enclosperm. These results show that the proteins in vitreous endosperm have a higher degree of cross-linking and a greater M, distribution than those found in floury enclosperm.