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The complete amino acid and nucleotide sequence of a secreted metalloprotease produced by Actinobacillus pleuropneumoniae serotype 1 is reported. A clone showing proteolytic activity in cell-free culture media was selected from a genomic library of A. pleuropneumoniae serotype 1 in pUC 19. The sequence obtained contained an open reading frame encoding a protein with 869 amino acids. This protein was identified as a zinc neutral-metalloprotease belonging to the aminopeptidase family, with a predicted molecular weight of approximately 101 kDa. This sequence showed high homology with other predicted or sequenced aminopeptidases reported for different Gram-negative bacteria. Expression of the protease was observed in lung tissue from pigs that died of porcine pleuropneumonia suggesting a role in pathogenesis.

To go further into the characterization of the proteolysis exocellular system of the salmonid pathogen Flavobacterium psychrophilum, the purification and characterization of a novel protease designated Fpp2 (F. psychrophilum protease 2) was undertaken. A protease (Fpp2) hydrolyzing azocasein was purified. The Fpp2 can be defined as a metalloprotease, it had an estimated molecular mass of 62 kDa with calcium playing an important role in the thermostability of the enzyme. Proteolytic activity was optimal at pH 6.0-7.0 and 24 degrees C and activation energy for the hydrolysis of azocasein was determined to be 5.4 kcal mol(-1), being inactive at temperatures above 42 degrees C. All these results are characteristic of 'cold adapted enzymes'. Fpp2 proved to be a broad range hydrolytic enzyme because in optimal conditions it was able to hydrolyze matrix and muscular proteins. It can be concluded that the Fpp1, a previously characterized 55 kDa metalloprotease, and the Fpp2 protease were produced under different physiological conditions and were immunologically as well as biochemically different.