Isolation and characterisation of two extracellular metalloproteases from Aeromonas salmonicida ssp. salmonicida

Two extracellular metalloproteases were purified from a culture filtrate derived from Aeromonas salmonicida ssp. salmonicida . One enzyme, leucine aminopeptidase (LAP), which had a molecular mass 37 kDa, hydrolysed aminoterminal l ‐leucine and l ‐phenylalanine. The activity was inhibited by 1,10‐o‐phenanthroline, but not by EDTA. The addition of excess Zn 2+ to an o‐phenanthroline‐inhibited enzyme restored most of its activity. The peptidase was temperature stable, and had an optimum temperature and pH of 60 °C and 8, respectively. The other enzyme, metalloprotease 3 (MP3), which had a molecular mass 20 kDa, was an endoprotease, and hydrolysed azocoll and hide powder‐azure, but not gelatine. The MP3 enzyme had an optimum temperature and pH of ≈40 °C and 7.5, respectively, and a cationic isoelectrical point.