Further characterization of DPP IV-beta, a novel cell surface expressed protein with dipeptidyl peptidase activity.

By using a CD26 negative human lymphoblastoid cell line (C8166), here we describe the characterization of a cell-surface protein which manifests CD26-like dipeptidyl peptidase IV (DPP IV) activity. This protein, referred to as DPP IV-beta, shows a higher KM value for Gly-Pro-pNA than CD26 (0.31 mM compared to 0.11 mM, respectively). In addition, DPP IV-beta was found not to bind 125I-labeled adenosine deaminase (a property of human CD26). Gel filtration experiments using extracts from C8166 and MOLT4 (a CD26 positive human T cell line) cells, revealed that the apparent molecular mass of DPP IV-beta is 82 kDa, whereas that of CD26 is 110 kDa. In order to conveniently differentiate both activities, a new family of inhibitors, that selectively blocks peptidase activity associated to CD26, has been developed.