Polypeptide or peptide deformylase; a family of metalloenzymes that catalyzes the removal of the N-terminal formyl group in a growing polypeptide chain following translation initiation during protein synthesis in prokaryotes. These enzymes utilize Fe(II) as the catalytic metal ion, which can be replaced with a nickel or cobalt ion with no loss of activity. There are two types of peptide deformylases, types I and II, which differ in structure only in the outer surface of the domain. Because these enzymes are essential only in prokaryotes (although eukaryotic gene sequences have been found), they are a target for a new class of antibacterial agents.