Dipeptidyl peptidase-4 (DPP4), also known as adenosine deaminase complexing protein 2 or CD26 (cluster of differentiation 26) is a protein that, in humans, is encoded by the DPP4 gene. The substrates of CD26/DPP4 are proline (or alanine) containing peptides and include growth factors, chemokines, neuropeptides, and vasoactive peptides. DPP4 plays a major role in glucose metabolism. It is responsible for the degradation of incretins such as GLP-1 and hence its inhibition by drugs such as Sitagliptin have been used for treatment of diabetes mellitus type 2. DPP4 also appears to work as a suppressor in the development of cancer and tumors. In BioVision's DPP4 Activity Assay Kit, DPP4 cleaves a substrate to release a quenched fluorescent group,