Albumins and Globulins in Maize Grains

Abstract

The proteins contained in maize caryopsis were divided by Osborne into albumins (water-soluble), globulins (salt-soluble), prolamins (alcohol-soluble), and glutelins (residual proteins, alkali-soluble when extracted). The characterization of glutelins, through amino acid analysis in particular, have suggested that they represent a mixture of albumins, globulins, and prolamins not extracted in the presence of water, salt, and alcohol (Mossé et al. 1966a). From this idea, Moureaux and Landry (1968) showed that three subgroups (G1, G2 and G3) of glutelins could be solubilized by a reductant in the presence of alcohol, salt, and detergent, respectively. Glutelins G1 (termed prolamin-2 by Sodek and Wilson (1971 a) or water-insoluble alcohol-soluble-reduced glutelins by Paulis and Wall (1977) and G3 have been found by Landry and Moureaux (1970) to have amino acid composition similar to that of prolamins (zein) and salt-soluble proteins, respectively, whereas glutelins G2 (termed water-soluble alcohol-soluble reduced glutelins by Paulis and Wall 1977, or reduced soluble proteins by Wilson et al. 1981) were unique. In spite of these differences, G1-and G2-glutelins have been designated by Esen (1986) as β-and γ-zein, respectively, to emphasize similarities of extractibility, composition, localization in grain and cell, and physiological role with zein (termed α-zein). Such a regrouping under the term of endosperm-specific proteins had been reported previously by Landry and Moureaux (1976) in a quantitative study of accumulation of protein fractions in developing grain. Zeins, because of their quantitative prevalence and their deficiency in lysine and tryptophan, considerably influence the nutritional quality of grain proteins and, thereby, have been the subject of numerous works for gaining insight into the molecular, genetic, and agronomic origins of their accumulation in grain.