Proteins of acha (Digitaria exilis Stapf): Solubility fractionation, gel filtration, and electrophoresis of protein fractions

Abstract

Proteins from Digitaria exilis (acha) and durum wheat were characterised by gel filtration (GF), sodium dodecyl sulphate polyacrylamide-gel electrophoresis (SDS-PAGE), and acid-PAGE. The proteins of acha show compositional and solubility differences from those of durum studied under the same conditions. From the acid-PAGE results, 1m urea extracted the gliadins of wheat. However, a urea concentration of up to 6m was necessary to solubilise acha proteins corresponding to α-gliadins. The proportion of glutelins and residue proteins in acha was higher than all other Osborne fractions. The amino-acid composition for acha-protein fractions showed significantly greater amounts of hydrophobic and sulphur amino acids than those in durum. The enhanced solubility of acha proteins in urea or propanol (in the presence of a reducing agent) suggests that hydrophobic as well as covalent disulphide interactions are responsible for the relative insolubility of acha proteins in conventional solvents. SDS-PAGE analysis of wholemeal acha flour revealed that a major component with molecular weight 25.2 kDa, which was absent in durum wheat, forms a basic structural component of acha storage proteins. GF and SDS-PAGE of the four soluble-protein factions for acha proteins (albumin, globulin, prolamin, and glutelin) showed that similar-molecular-weight components (obtained by GF) were relatively heterogeneous by SDS-PAGE. © 1994.