Aggregation states of alcohol-soluble storage proteins of barley, rye, wheat and maize.

Abstract

AbstractTwo approaches were used to study the aggregation states of prolamins extracted from milled whole grain of wheat, barley, rye and maize with 500 ml litre−1 aqueous propan‐1‐ol. In the first, a comparison was made of the electrophoretic patterns of the samples separated by sodium dodecylsulphate polyacrylamide gel electrophoresis (SDS‐PAGE) under reducing and non‐reducing conditions. In the second, they were chromatographed on a column of controlled pore glass (CPG) using a modified acetic acid, urea, cetyltrimethyl ammonium bromide (AUC) solvent and aliquots of the major peaks were reduced and analysed by SDS‐PAGE. When the CPG chromatography was repeated under reducing conditions some of the peaks were eliminated indicating that they were composed of disulphide‐linked aggregates. The results from both approaches showed that in barley, rye and wheat the HMW prolamins and some of the S‐rich prolamins (B hordein, some γ‐secalins and subunits of high molecular weight gliadins) are present predominantly or partially in high molecular weight (above 1 × 106 daltons) aggregates which appear to be stabilised by disulphide bonds. Other S‐rich prolamins (including some γ‐secalins, α, β and γ‐gliadins) and all the S‐poor prolamins (‘C’ hordein, ω‐secalin, ω‐gliadin) are present predominantly or only as monomers. These results are discussed in relation to the structural and genetic homology of the prolamins in the three species. Although prolamin aggregates are also present in maize, these are of lower molecular weight.