Molecular characterization of dipeptidyl peptidase activity in serum - Soluble CD26/dipeptidyl peptidase IV is responsible for the release of X-Pro dipeptides

Dipeptidyl peptidase IV (DPPIV, EC 3.4.14.5) is a serine type protease with an important modulatory activity on a number of chemokines, neuropeptides and peptide hormones. It is also known as CD26 or adenosine deaminase (ADA; EC 3.5.4.4) binding protein. DPPIV has been demonstrated on the plasmamemb ranes of T cells and activated natural killer or B cells as well as on a nu mber of endothelial and differentiated epithelial cells. A soluble form of CD26/DPPIV has been described in serum. Over the past few years, several re lated enzymes with similar dipeptidyl peptidase activity have been discover ed, raising questions on the molecular origin(s) of serum dipeptidyl peptid ase activity. Among them attractin, the human orthologue of the mouse mahog any protein, was postulated to be responsible for the majority of the DPPIV -like activity in serum. Using ADA-affinity chromatography, it is shown her e that 95% of the serum dipeptidyl peptidase activity is associated with a protein with ADA-binding properties. The natural protein was purified in mi lligram quantities, allowing molecular characterization (N-terminal sequenc e, glycosylation type, CD-spectrum, pH and thermal stability) and compariso n with CD26/DPPIV from other sources. The purified serum enzyme was confirm ed as CD26.