Sunflower Seed Proteins: Characterization and Subunit Composition of the Globulin Fraction

Abstract

Salt soluble proteins from sunflower (Helianthus annuus) seeds were fractionated by isoelectric precipitation and analysed by electrophoresis. Three molecular species were detected by gradient polyacrylamide gel electrophoresis of the globulin fraction. Multi-dimensional gel electrophoresis analysis indicates that all these species contained similar intermediary subunits of 60 000, 54 000, 48 000 and 40000 molecular weight, the two former being predominant. As shown by ion-exchange chromatography under dissociating and reducing conditions, the intermediary subunits are composed of disulphide linked pairs of large ‘acidic’ and small ‘basic’ subunits. Heterogeneity in molecular weight of these subunits was shown by electrophoretic studies. These results suggest that a major reserve protein in sunflower seeds is similar to ‘legumin’ of plants of the family Leguminosae.