PREP is a cytosolic prolyl endopeptidase that cleaves peptide bonds on the C-terminal side of prolyl residues within peptides that are up to approximately 30amino acids long. Prolyl endopeptidases have been reported to be involved in the maturation and degradation of peptide hormones and neuropeptides. Recombinant human PREP protein, fused to His-tag at N-terminus, was expressed in E.coli and purified by using conventional chromatography techniques.