Serine proteinase from rice bean

A trypsin like serine-proteinase of M(r) 16,000 Da, optimally active at pH 8.4 on N-benzoyl-arginine ethyl ester (BAEE) was purified from 4-day old germinated seeds of rice bean, Vigna umbellata (Thunb), by ammonium sulphate precipitation, gel filtration, ion-exchange chromatography and by high performance liquid chromatography (HPLC). The purity of the enzyme was checked by polyacrylamide gel electrophoresis (PAGE). The enzyme activity was studied on natural substrates like casein, haemoglobin and vicilin, a rice bean storage protein. The activity of the enzyme was completely inhibited by phenylmethylsulfonyl fluoride, but not by iodoacetamide and HgCl2, suggesting it to be a serine protease. Loss of activity in presence of EDTA was reversed by addition of Ca2+.