Abstract

Cysteine protease inhibitors (CPIs) are widespread in plant seeds and are attractive candidates for use in the pharmaceutical industry. Wonder bean (Canavalia ensiformis) is a climbing perennial legume with fascinating pharmacological properties. A distinguishing characteristic of this plant is its ability to thrive under extreme environmental conditions such as nutrient-depleted, highly leached and acidic soil. Plants that survive in these extreme environmental conditions are known for high effective protease regulation by protease inhibitors which include CPI. Study was therefore designed with the aim to isolate and characterize CPI from wonder bean. CPI from Canavalia ensiformis was isolated and purified by simple methods consisting ammonium sulphate precipitation, ion exchange chromatography and gel filtration. Mode of inhibition, optimum temperature and pH, as well as the effect of metals on the enzyme activity were determined using spectrophotometric method. The purified CPI was confirmed to be a competitive inhibitor against papain with the same Vmax = 78.59?103?mol/min, Km=209?M, and Ki = 137 ?M. The inhibitor exhibited maximal activity at temperature and pH of 40°C and 8.0 respectively. Metal cations such as, Pb2+, Mg2+,Co2+, Mn2+, Zn2+ and Cu2+ significantly inhibited CPI at a very low concentration (1mM). The SDS-PAGE analysis revealed two bands of molecular weight estimated to be 28 and 32 KDa. CPI from Canavalia ensiformis was successfully isolated and there was an indication that it is composed of two polypeptide chains that might have been denatured under reducing condition in the presence of ?-mercaptoethanol. However, further investigation is required to verify this.

Keywords: Canavalia ensiformis, Cysteine protease inhibitor, Papain, Purification, and Characterization