Sunflower seed protein: size and charge heterogeneity in subunits of the globulin fraction

The subunit heterogeneity of the globulin fraction of sunflower seeds was investigated by two dimensional electrophoresis, using isoelectric focusing in the first dimension and sodium dodecyl sulphate polyacrylamide gel electrophoresis in the second dimension. Under non reducing conditions, intermediary subunits B, C and D (molecular weight 54 000, 48 000 and 40 000, respectively) were focused within a pI range 5.4-6.0 but intermediary subunits A (molecular weight 60 000) focused within a pI range 6.3-6.8. Under reducing conditions the electrophoretic patterns show that intermediary subunits consist in large "acidic" and small "basic" subunits linked by disulphide bonds. The large subunits of B species are more acidic and less heterogeneous than the corresponding subunits of the A species. These results confirm that helianthinin had a "legumin-type" structure.