High·performance Liquid Chromatography of Cereal Proteins

Cereal endosperm storage proteins include primarily prolamins (the name derived from ·proline" plus "amine," generaHy proteins soluble in aqueous solutions of alcohols) and glutelins (proteins insoluble under neutral, nonacidic. nonreducing conditions in water. saline solutions, and alcohol but soluble in solutions containing acid. alkali. detergents. denaturants. or disulfide reducing agents) (Osborne. 1907). Albumins (soluble in water) and globulins (soluble in saline solutions but insoluble in water) are also present, but to lesser extents. Recent reviews (Kasardaet aI, 1976; WaH and Paulis. 1978; WaH. 1979; Bright and Shewry', 1983; Payne and Rhodes. 1983; Shewry et al. 1984) summarize current knowledge of the origins, structures. properties, and relationships of these proteins. which are of great functional and nutritional importance. Analysis of cereal proteins may be extremely difficult. Cereal proteins are very heterogeneous. often being products of large multigene families. Their solubilities are also atypical of most other plant or animal proteins. resulting from their unusual amino acid compositions (generaHy rich in glutamine. proline. and hydrophobic amino acids and deficient in acidic and basic residues). Thus. analytical methods for other proteins may not succeed with cereal proteins. Finally, many cereal proteins interact noncovalently with endosperm constituents such as lipids and carbohydrates. and associate, either noncovalendy through hydrogen or hydrophobic bonds or covalently through disulfides. with each other to form high-molecular-weight (HMW) complexes. In spite of these difficulties. several analytical methods permit isolation and characterization of cereal endosperm proteins. After initial demonstratIons (Jones et al. 1959) showed that cereal proteins could be separated by moving boundary electrophoresis. methods were developed using porous starch. polyacrylamide, or agarose gel matrixes (for reviews see Wrigley, 1977; Bietz, 1979', Wrigley et aI, 1982) to separate proteins in three ways. In starch gel electrophoresis or polyacrylamide gel electrophoresis (PAGE). proteins are