CHARACTERIZATION OF PARTIALLY PURIFIED MILK-CLOTTING KESINAI (STREBLUS ASPER) PROTEASE.

Proteases with milk clotting can be isolated from plant sources and this study kesinai (Streblusasper) leaves contain a protease, which could be used to coagulate the milk for the alternative source for calf rennet. The present investigation was undertaken to characterize the partially purified kesinai protease. The enzyme function optimally at 60 oC and pH 7.4 and it showed higher temperature stability at -10oC and 4 oC. It retained more than 98% of its activity 7 days after storage at both -10 and 4 0C. The enzyme was inhibited by PMSF and trypsin inhibitor by 98% and 95.87% of initial activity, respectively. However, antipain, pepstatin A, N-ethylmaleimide, EDTA, O-phenanthroline and β-mercaptoethanol showed no significant inhibitory effect suggesting the presence of serine residue at the active site. Ca2+ had a slight stimulating effect on the enzyme activity. On the other hand, Hg2+, Zn2+ and Pb2+ had inhibitory effects on the enzyme activity. The enzyme was also partially inhibited by Mg2+, Co2+, Cu2+, Ni2+ and Al3+. Kesinai protease exhibited the highest specific activity towards azo- casein compared to casein, haemoglobin, bovine serum albumin (BSA) and gelatin. The protease also had a Km of 2.6 mg/mL for azo- casein while Milk clotting activity of kesinai was lower than commercially produce mucor rennet.