Purification and Characterization of a Rice Cysteine Proteinase Inhibitor

Abstract

A proteinaceous substance that inhibited the activity of papain (EC 3.4.22.2) was found in seeds of rice, Oryza sativa L. japonica. This cysteine proteinase inhibitor (CPI) was purified by a series of purification procedures including CM-Sephadex C-50, Sephadex G-75, and DEAE-Sephadex A-50 chromatography. The CPI was a single polypeptide with a molecular weight of about 12,000, with an isoelectric point at pH 5.3. The CPI was stable below 100°C and between pH 2.2 ~ 9.0. The inhibition of papain by the CPI was non-competitive, with a Ki value of 2.44 x 10-8M. The complete inhibition of papain was reached by an equimolar concentration of the CPI. © 1987, Japan Society for Bioscience, Biotechnology, and Agrochemistry. All rights reserved.