Variation in estimates of molecular weights of cereal prolamins by SDS-PAGE

The total reduced, alcohol-soluble protein fractions from barley, wheat, rye, maize, millet and sorghum, which we term ‘prolamin’ fractions, were separated using three systems of Polyacrylamide gel electrophoresis in the presence of sodium dodecyl sulphate and the relative molecular masses (Mrs) of the major components determined by comparison with the mobilities of standard proteins. Three types of errors were identified for prolamins of the Triticeae: over-estimation of Mrs compared with those determined by physical methods or from protein sequences, increases in Mrs due to the inclusion of urea in the gels and differences between Mrs determined, in the absence of urea, by different systems. Although different gel systems also gave different Mrs for some prolamins of the Panicoideae, the inclusion of urea had no effect. The results are discussed in relation to the amino acid compositions and secondary structures of the proteins