Human serum dipeptidyl peptidase IV (DPPIV) and its unique properties

Dipeptidyl peptidase IV (DPPIV, EC 3.4.14.5) has been purified 18,000-fold in a yield of 2.2% from human serum. Serum DPPIV, a serine enzyme with an apparent mass of 250 kDa, consists of two identical subunits with an apparent mass of 100 kDa and is inhibited by DPPIV-specific inhibitor Diprotin A and also by p-chloromercuribenzoate (p-CMB), 2-mercaptoethanol, HgCl2, CdCl2, SrCl2, and ZnCl2. One of the remarkable properties of DPPIV is that its activity is greatly enhanced by Gly-X (X: especially, Gly, Gln, Glu and Ser) dipeptides. Gly-X dipeptides increase not only an apparent Km of serum DPPIV for glycyl-L-proline 3,5-dibromo-4-hydroxyanilide nearly 10-fold, but also an apparent kcat nearly 4-fold. This mechanism is unclear, but one possibility is that Gly-Pro from substrate might bind amino acids or dipeptides instead of water molecules as DPPIV transpeptidyl activity reported previously. Another remarkable property of DPPIV is the ability to bind adenosine deaminase-I and -II, as is the case with recombinant soluble CD26 (rsCD26). This probably indicates that DPPIV purified from human serum by our method originates from T-lymphocytes.