A peptidyl dipeptidase-4 from Pseudomonas maltophilia: purification and properties

A peptidyl dipeptidase-4 (bacterial PDP-4) was purified to near homogeneity from a supernatant of Pseudomonas maltophilia extracellular medium. Bacterial PDP-4 is a single-polypeptide-chain enzyme, 82 kDa, with an alkaline isoelectric point. Peptides susceptible to hydrolysis by bacterial PDP-4 include angiotensin 1, bradykinin, enkephalins, atriopeptin 2, and smaller synthetic peptides. N-acylated tripeptides are hydrolyzed, but free tripeptides are not. A free carboxy terminus is required for hydrolysis. Peptides with ultimate and penultimate Pro residues are not hydrolyzed. The enzyme does not require an anion for activity. Bacterial PDP-4 was inhibited by EDTA and the dipeptide Phe-Arg. Thiorphan was an inhibitor only at levels well above those required for inhibition of neutral metalloendopeptidase (NEP), an enzyme for which thiorphan is specific. A second NEP and thermolysin inhibitor, phosphoramidon, did not inhibit bacterial PDP-4. The potent angiotensin-converting enzyme inhibitor lisinopril was not inhibitory. Bacterial PDP-4 is distinguished from a similar enzyme from Escherichia coli, which is not susceptible to EDTA inhibition, and one from Corynebacterium equi, which hydrolyzes free tripeptides. These data indicate that the bacterial PDP-4 catalytic site is unlike those of other enzymes that function either wholly or in part as peptidyl dipeptidases.