Disulphide mapping of a methionine-rich 2S albumin from sunflower seeds showed four intra-chain disulphide bonds which are homologous with those in a related heterodimeric albumin from lupin seeds (conglutin 5). Similar conserved disulphide bonds are also present in c~-gliadin and T-gliadin storage proteins of wheat, but a lower level of conservation is present in a further related group of proteins, the cereal inhibitors of c~-amylase and trypsin. These differences may relate to the different functions of the proteins.

We have elucidated the complete amino acid sequence of one of the avenin components, avenin-3, isolated from oat (Avena sativa L.), variety Narymsky 943. The sequence of the protein was determined by sequencing of CNBr and trypsin-generated peptides in combination with mass spectrometry. The protein is a single polypeptide chain, consisting of 201 amino acid residues with M, 23252.8. The N-terminal amino acid residue of the protein is blocked with 5-oxoproline (pyroglutamic acid). All eight cysteine residues in avenin-3 are involved in disulphide bonds. The positions of these bonds were established by identification of a CNBr cleavage product of the intact avenin containing all the disulfide bonds (S-S core). Subsequent subdigestion of this S-S core allowed isolation of disulphide bonded peptides detected by differential reverse-qhase HPLC before and after reduction. As a result, all four disulphides Cys50 Cys183, Cys58 Cys77, Cys84 Cys85 and Cys97 Cysl91 were identified. Comparison of avenins with other prolamins demonstrates a high degree of similarity, which is especially pronounced around the cysteine residues. Avenins differ slightly from other prolamins in having unique N-terminal sequences and some differences in the repeated sequence motifs.

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