Glutelin subunits

RP-HPLC is especially valuable in genetic studies of maize. Paulis et al. [175] showed that prolamin RP-HPLC differentiates normal, opaque-2, and modified opaque-2 genotypes differing in nutritional quality and endosperm texture. Modified opaque-2 maize genotypes ( quality protein maize ) are enriched in high-proline alcohol-soluble glutelin subunits and contain less zein than normal maize. 

Many cereal endosperm storage proteins—especially glutelins— are, in their native forms, disulfide-bonded oligomers or polymers. Even if soluble, such proteins may resolve poorly upon RP-HPLC and elute as broad peaks [22], in part due to their many possible polymeric forms. Reduction is necessary to release disulfide-bonded subunits from cereal glutelins or oligomeric prolamins for analysis [19,32,42,76]. Thus, protein resolution, extractability, and stability are often improved by extraction under reducing conditions. To prevent reoxidation and further enhance resolution, resulting cysteine residues may be stabilized by alkylation, usually with 4-vinylpyridine [19,21,29,70,76]. 

The high-molecular subunits of wheat glutelins show a protein pattern typical of the cultivar (Fig. 15.8). 

Fig. 15.7. RP-HPLC of low-molecular (LMW) subunits of wheat glutelin of the cultivar Rektor on Nu-cleosil Ci8 (60 °C, aqueous 2-propanol/trifluoroacetic acid/acetonitrile. After the prolamins, the protein fraction was extracted from the residue with 70% aqueous ethanol/0.5% dithioerythritol at pH 7.6 and 4 °C peaks 2-4, 5-7 co5-, col,2-gliadins. Peaks 8-17 LMW subunits, peaks 20-25 y-gliadins or related proteins, according to Wieser et al., 1990)...

Fig. 15.8. RP-HPLC of the high-molecular (HMW) subunits of the glutelins of different varieties of wheat on Nucleosil Cg (60 °C, urea/trifluoroacetic acid/acetonitrile/dithioerythritol numbering of the peaks 1-7 (x-type), 8-12 (y-type)) (FAR Farmer, CWR Canadian Western Red Spring, APO Apollo, CHI Chinese spring according to Seilmeier et al., 1991)...

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