Limited Tryptic Degradation of Urea Denatured Glycinin

Abstract

Digestibilities of native, 5M urea-denatured and 8M urea-denatured glycinin were studied. Urea was removed by dialysis before digestion. The tryptic digestion of the proteins are influenced by ionic strength. Under low ionic strength condition (0M NaCl), the proteins, even native glycinin, are well degraded. On the other hand, under high ionic strength con-dition (0.5M NaCl), native glycinin resists the tryptic attack and 5M urea-denatured glycinin is best degraded. The digestibility of 8M urea-denatured glycinin is lower than that of 5M urea-denatured one under the condition. The gel filtration and electrophoretic properties show that the digestion intermediate like glycinin-T (the intermediate from native glycinin) is contained in the digestion products. These suggest that the urea-denatured protein contains the almost renatured component after removal of urea. A larger amount of the glycinin-T-like protein was detected at 8M urea denaturation than at 5M urea. Therefore, glycinin renatures more readily from 8M urea denaturation. Probably this is the cause of the decreased digestibility at 8M urea denaturation.