Biochemical characterization of an alkaline metallopeptidase secreted by a Pseudomonas fluorescens isolated from soil

The extracellular endopeptidase synthesized by soil bacterium Pseudomonas fluorescens was purified to homogeneity in a four-step procedure. The enzyme was purified 45-fold, with a 20% recovery. The endopeptidase appeared to be a monomer with a molecular mass of approx. 50 kDa. The enzyme was active in the pH range of 7 to 10. The optimal activity was detected at pH 9.0 and at 42 degrees C. Enzyme activity was inhibited by EDTA, EGTA and 1,10 phenanthroline, typical metalloprotease inhibitors. Ca(2+) activated the enzyme while Zn(2+), Co(2+), Cd(2+)(in high concentration) strongly inhibited it. The presence of calcium ions strongly stabilized the enzyme with regard to thermal resistance. The amino acid sequence of fragments of the enzymatic protein determined by MS analysis revealed a high similarity to the sequences of other alkaline metalloendopeptidases of bacteria belonging to the genus Pseudomonas.