HEAT DENATURATION OF SOYBEAN PROTEINS .2. INFLUENCE OF HEATING TEMPERATURE ON CONFORMATIONAL-CHANGES OF SOYBEAN PROTEINS

Changes of ultracentrifugal patterns of soybean proteins by heating up to 100°C were almost completed at SO°C at lower ionic strength and at 90°C at higher ionic strength. However, changes in DTNB reactive sulfhydryl groups, sulfite reducible disulfide bonds, ultraviolet difference spectra and turbidity of the protein solutions were still observed at temperatures higher than 80 or 90°C. These results suggest that 11S protein dissociates into subunits at a temperature below 80 or 90°C, and that the conformations of these subunits can change at a temperature above SO or 90°C. When heated at high ionic strength, the protein solution became turbid because of aggregation of proteins. SDS polyacrylamide gel electrophoresis showed that aggregated proteins separated by centrifugation as precipitates were formed from low-molecular-weight subunits of lIS protein and non-aggregated proteins remaining in the supernatant were from 7S protein and high-molecular-weight subunits of 11S protein. © 1979 Taylor & Francis Group, LLC.