PEPTIDE-BOND HYDROLYSIS EQUILIBRIA IN NATIVE PROTEINS . CONVERSION OF VIRGIN INTO MODIFIED SOYBEAN TRYPSIN INHIBITOR

Virgin (Arg(64)-IIe(65) bond intact) and modified (Arg(64)-IIe(65) bond cleaved) soybean trypsin inhibitor were separated by preparative disc gel electrophoresis. Incubation of either the virgin or the modified inhibitor with catalytic quantities of trypsin at pH 4.00 and 20° yields the same equilibrium mixture containing 86 ± 2% of modified and 14 ± 2% of virgin inhibitor as judged by analytical disc gel electrophoresis. Thus, the existence of an equilibrium between these two forms is conclusively demonstrated. Preliminary values of the equilibrium constant as a function of pH were obtained. As expected, there is a broad minimum (Khydroiysis ˜ 2) in the pH 5-8 range and sharp increases at both high and low pH values. © 1969, American Chemical Society. All rights reserved.