Proteinase Inhibitors in Plant Seeds

Part IV Trypsin-inhibitor Complex Formation

Abstract

Inhibitors I (R-I) and III (R-III) obtained from Japanese radish seed were employed to investigate their interaction with trypsin. The trypsin-inhibitor complex was isolated by gel-filtration on Sephadex G-75. Second order rate constants of the complex formation were 5.8×106M^-1. sec^-1 and 1.1×10⁶M^-1. sec^-1 for trypsin-R-I and trypsin-R-III, respectively. The complex dissociated in an acidic pH range (pH 2_??_5) and the dissociation constant was dependent on pH. pH-dissociation curves were sigmoidal. The K_diss. value at pH 8 was approximately calculated as 10^-10M. The R-III-trypsin complex was also dissociated (by treatment with protein denaturants and by heat treatment, ) in proportion to inactivation of the enzyme.