Zein of maize grain: II--The charge heterogeneity of free subunits

The subunits present as monomers in unreduced zein and isolated as fraction M by gel filtration, were chromatographed on sulfoethyl-cellulose. Three major subfractions were detected and characterized. Each of them, submitted to electrophoresis at pH 3.5, migrated as a single band corresponding to each of the three major electrophoretic forms seen in fraction M at the same pH. The presence of lysine in some polypeptides, suggested by amino acid composition data, was confirmed by electrophoretic analysis of carbamylated subfractions at pH 3.5. At pH 8.9 each subfractions was further resolved into three cationic bands in starch gel and three (or more) anionic bands in polyacrylamide gel. The same fractionation was also obtained by submitting the major electroforms of fraction M, as isolated at pH 3.5, to isoelectric focusing. Based on these observations, the most probable distributions of basic amino acids in subunits detected by electrophoresis at pH 8.9 were specified and compared to those recently published for several zein clones. The presence per polypeptide chain of three carboxyl groups and occasionally of one lysine would be a feature of zein originating from maize hybrid Inra 260.