Cold-active serine alkaline protease from the psychrophilic bacterium Pseudomonas strain DY-A:: enzyme purification and characterization

An extracellular protease was purified from a deep-sea psychrophilic bacterium strain DY-A which was identified as a Pseudomonas species. The optimal growth and protease-producing temperatures of the strain were all 10degreesC, and the protease was secreted only at temperatures under 20degreesC. The enzyme was most active at 40degreesC and at pH 10.0. It was inhibited by phenylmethyl sulfonylfluoride and diisopropyl fluorophosphate, indicating that it is a serine protease. Chelators such as EDTA, EGTA, 1,10-phenanthroline and 2,2'-bipyridyl produced a decrease of activity. The enzyme was sensitive to denaturing agents such as SDS, urea, and guanidine HCl and resistant to thiol-containing reducing agents such as dithiotreitol. The enzyme was active towards N-succinyl-Ala-Ala-Pro-Phe-p-nitroanilide and N-succinyl-Ala-Ala-Pro-Leu-p-nitroanilide. The native molecular mass of the enzyme determined by native PAGE and SDS-PAGE was 25 kDa.