Proline iminopeptidase (PepIP) is a major peptidase in subsp. CNRZ397, encoded by the gene. Amplification and expression of this gene in K12 resulted in a very high level of enzyme production. Moreover, export into the periplasm of 45% of PepIP activity allowed us to purify the enzyme easily by a single ion-exchange chromatography step. PepIP is a trimer of M 100000, composed of three identical subunits. In the presence of 0•1 % BSA, PepIP activity was optimal at pH 6–7 and stable at temperatures below 40°C. The enzyme was strongly inhibited by 3,4-dichloroisocoumarin, a serine protease inhibitor, by bestatin and by heavy metal ions. It was also inactivated by -chloromercuribenzoate, but was reactivated by adding dithiothreitol. PepIP is characterized by a high specificity towards di- or tripeptides with proline at the NH-terminal position, but is not able to hydrolyse longer peptides, or peptides with hydroxyproline at the NH-end. The NH-terminal amino acid sequence of the purified PepIP corresponds to the amino acid sequence deduced from the nucleotide sequence of the gene.


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