PGPEP1 is an omega peptidase which removes pyroglutamyl residues from the amino termini of peptides and proteins. It is a cytosolic cysteine peptidase that is expressed in most cell types. The enzyme requires a thiolreducing agent for activity. PGPEP1 is potentially involved in the inactivation of biologically active peptides that possess an amino terminal pyroglutamyl group. Examples of such peptides include neurotensin, luteinizing hormone releasing hormone, and thyrotropinreleasing hormone. Recombinant human PGPEP1 protein, fused to His-tag at N-terminus, was expressed in E.coli and purified by using conventional chromatography techniques.