Characterization of the bacterial metalloendopeptidase pitrilysin by use of a continuous fluorescence assay.

Pitrilysin (EC 3.4.99.44) has been purified from an over-expressing strain of Escherichia coli. A 13-residue quenched-fluorescent-peptide substrate for the enzyme has been synthesized, and found also to be cleaved by the homologous enzyme, insulinase (EC 3.4.99.45). The action of pitrilysin on peptides and proteins was studied: insulin B chain was the most rapidly degraded, small peptides down to 10 residues in length were cleaved more slowly, intact insulin was cleaved very slowly but with a very low Km, and there was no action on the larger proteins tested. Since the activity of pitrilysin is confined to substrates smaller than proteins, it can be described as an endopeptidase of the 'oligopeptidase' type, and like other such enzymes, it did not interact with alpha 2-macroglobulin. The metal-dependence of pitrilysin was confirmed, and it was found to be inhibited by bacitracin, especially in the presence of zinc.