DPP2 is a serine protease found most abundantly in the lysosome. There is also a non-lysosomal membrane-associated form of DPP2 reported in the rat brain (DPP-II-M), and a soluble form (DPP-II-S). First discovered as an enzyme involved in the terminal steps of protein degradation, and later as an enzyme involved in cell growth and quiescence, DPP2 cleaves N-terminal dipeptides and tripeptides from proteins. DPP2 has a preference for proline in the P1 position, and processes the tripeptides generated by DPP1 (which is unable to cleave if proline is in the P1 position). Some tumor cell lines express elevated DPP2 levels, and serum levels of DPP2 are elevated in some cancer patients, making DPP2 a potential tumor marker. DPP2 levels have been also been reported to be elevated in the cerebral spinal fluid from Parkinson’s patients.