Purification and characterization of a gelatinolytic serine protease from the seeds of ash gourd <em>Benincasa hispida</em> (Thunb.) Cogn.

Abstract

In Ayurveda, <em>Benincasa hispida</em> (Thunb.) Cogn. (Ash gourd) was recommended for management of diabetes, peptic ulcer, and other diseases. This plant is rich in proteolytic enzymes and proteases have wide application in food and laundry industry. Therefore, the search for new potential plant proteases continues. A soluble gelatinolytic plant serine protease (AG2) had been purified from the seeds of <em>Benincasa hispida</em>. The molecular mass of the monomer was estimated to be about 11 kDa by SDS-PAGE and 11211.1 Da by MALDI-TOF. The protease activity was strongly inhibited by PMSF only but not at all by soyabean trypsin inhibitor and resists autodigestion. Thus AG2 belongs to subtilisin family. The optimum pH and temperature are 10.0 and 30°C respectively. This protease was quite stable in presence of a cationic surfactant, an oxidizing agent and in basic pH medium. The protease AG2 can hydrolyze casein, azoalbumin and TAME but it was inert towards BAPNA. The kinetic parameters K_m and V_max were 0.117 ± 0.00067 mM and 470.592 ± 0.631 unit mg^-1 min^-1 respectively using casein as substrate. The CD spectrum showed it as a typical α/β class of protease. The N-terminal sequence of first 17 amino acid residues (MQQFFNEPSSLLIVVVR) is unique in nature.