The storage protein fraction of barley, called hordein, is classified as a prolamin. It constitutes some 35–55% of the proteins of the endosperm depending on the variety and N nutrition of the plant1.The prolamins are characterized by their extractability and solubility in alcoholic solvents which increases in the presence of reducing agents, their amino acid composition and their presence in protein bodies (see2 for a review). In our laboratory hordein is routinely extracted in 55% propan-2-ol and 2% 2-mercaptoethanol and the cysteine residues alkylated with 4-vinyl pyridine (3,4) before further characterisation. The component polypeptides are then separated by either sodium dodecyIsulphate polyacrylamide gel electrophoresis (SDS-PAGE), urea-PAGE or isoelectric focusing (IEF) in one dimension or by IEF/SDS PAGE or urea-PAGE/SDS-PAGE in 2-dimensional systems3,4,5,6. Based on electrophoretic separations hordein was originally separated into α, β, γ, δ and e fractions7,8 although now this is usually simplified into A, B and C fractions9,5. The A fraction is relatively high in lysine and is probably not a true storage protein (see discussionin10). The B and C fractions have been separated and purified and various of their characteristics determined11 (Table 1).
