Isolation and Characterization of Organic-Solvent Stable Protease Isolated by Pseudomonas stutzeri BK AB-12

In this study, proteases have been isolated from halophilic bacteria, Pseudomonas stutzeri BK AB-12. The bacteria produced proteases as exhibited by the appearance of clear zones resulted from casein hydrolysis. Based on the protease specific activity, 70−80% ammonium fraction exhibited the highest activity. Protease in this fraction has highest activity at pH 8.0 and 55 °C and its activity of protease was enhanced by the addition of several metal ions. The addition of Fe3+ ion also resulted in a shifting of the optimum pH from 8 to 9 and the optimum temperature from 55 to 60 °C. Protease of P. stutzeri BK AB-12 in the fraction of 70−80% is not likely metallo-, cysteine-, or serine-protease because it is not inhibited by EDTA, β-mercaptoethanol, and PMSF. Proteases of this fraction was sensitive to ionic strength, where the highest activity was observed at concentrations at NaCl concentrations of 2.5 M. Beside influenced by the ionic strength, protease activity was also sensitive to solvent polarity. The protease wasstable in the presence of different organic solvents, which enables its potential use for the synthesis of peptides.