C-13 NMR-STUDIES OF THE EFFECTS OF GELATION AND HEAT AND CHEMICAL DENATURATION AT NEUTRAL PH ON SOY GLYCININ AND BETA-CONGLYCININ

Carbon-13 NMR studies have been carried out on soy glycinin and β-conglycinin under conditions of gelation and heat and chemical denaturation in pH 7.0 aqueous solutions containing 0.035 M phosphate and 0.4 M NaCl. With 6 M urea as a chemical denaturant, major changes were seen in the appearance of the aliphatic and aromatic carbon regions of the protein spectra, particularly in that of β-conglycinin. However, carbon chemical shifts underwent little or no change during denaturation, confirming that the sharp peaks observed in the native proteins were largely from mobile groups in random regions. As the temperature of the protein solutions was increased, many additional peaks were observed, especially in β-conglycinin, and existing peaks in both proteins became sharper, consistent with increased molecular motion and protein unfolding. Upon gelation, both protein gels gave spectra consistent with involvement of aliphatic and aromatic amino acids in gel structure. The β-conglycinin gel also showed evidence of the involvement of the carbohydrate and glutamate side chains in gel structure. The data support the concept that gelation of both proteins is a four-step process involving (1) unfolding (different from denaturation), (2) aggregation, (3) strand formation, and (4) strand ordering/gelation. © 1990, American Chemical Society. All rights reserved.