Removes 5-oxoproline from various penultimate amino acid residues except L-proline. Release of an N-terminal pyroglutamyl group from a polypeptide, the second amino acid generally not being Pro. Inhibited by transition metal ions including Ni(2+), Zn(2+), and Cu(2+) and by sulfhydryl-blocking agents. Monomer. Belongs to the peptidase C15 family.