Growth of Pseudomonas FC-1 on ferrichrome A or exposure of the cells to this cyclic peptide induced the formation of an alkaline peptidase. Enzyme induction, which was inhibited by chloramphenicol, could not be obtained with general proteinaceous substrates such as peptone. The peptidase opens the ring of ferrichrome A at an acyl serine bond. The product, a linear hexa-peptide, was isolated and characterized. An assay for the peptidase was developed, based on periodate oxidation of the newly formed N-terminal serine residue, followed by determination of formaldehyde via chromotropic acid. The enzyme, which is intracellular, was isolated in soluble form from ferrichrome A-grown cells by treatment of an acetone powder with snake venom in slightly alkaline medium. A 40-fold purification was achieved by ammonium sulfate precipitation and gel filtration on Sephadex G-100. The purified enzyme was neither strongly activated nor inhibited by a series of divalent metal ions; sulfhydryl reagents did not destroy the activity. The pH optimum was about 9.0. © 1965, American Chemical Society. All rights reserved.