The effect of sulfhydryl groups and disulphide linkage in the thermal aggregation of Z19 alpha-zein.

Zeins are the major storage proteins in corn seeds organized in protein bodies located in the endosperm. They are soluble in alcoholic solution and depict a high tendency to aggregation. The Z19 alpha-zein aggregates obtained by heating show a particular and interesting temperature-dependent behavior. This work was aimed at determining not only the effect of temperature on the aggregation behavior, but also the effect of the sulfhydryl groups and disulphide bonds on the thermal aggregation process under non-aqueous conditions. Z19 alpha-zein was chemically modified to obtain different sulfhydryl groups and disulphide-bonds content. Far-UV CD, ANS emission fluorescence, and dynamic light scattering, as well as differential scanning calorimetry, were performed to characterize this protein. Removal of these disulphide-bonds and alkylation of all the sulfhydryl groups in the protein promoted the lowest T(m) of 57.36 degrees C, eliminated aggregation, enhanced protein flexibility, and diminished thermal stability. These results suggest that the disulphide linkage could be the driving force for the Z19 alpha-zein aggregation.