CHARACTERIZATION OF DIPEPTIDYL PEPTIDASE-IV (CD26) FROM HUMAN-LYMPHOCYTES

The membrane-bound dipeptidyl peptidase IV (DPP IV, EC 3.4.14.5) has been purified 5,400-fold from human peripheral blood mononuclear cells. The purification procedure included detergent solubilization and successive chromatography on DEAE Sepharose(R) Fast Flow, Con A Sepharose(R), Cu2+ loaded metal-chelating Sepharose(R), Sephacryl(R) S-300 High Resolution and Q Sepharose(R) Hiload. The molecular mass of the native, detergent solubilized enzyme estimated by gelfiltration was 264 kDa. Chromatofocusing indicated a pI of approximately 5.0. The pI optimum was 8.7. The enzymatic activity of the purified preparation was irreversibly inhibited by N-(H-Phe-Pro-)-O-(4-nitrobenzoyl)hydroxylamine hydrochloride in the micromolar range. The binding of purified DPP IV to CD26 monoclonal antibodies confirmed the identity between CD26 and dipeptidyl peptidase IV. The purification and characterization of lymphocytic dipeptidyl peptidase IV is of great value for the identification of its natural substrates and for the study of its physiological significance in the T-lymphocyte function.