Inhibition of dipeptidyl peptidase IV (DP IV) by anti-DP IV antibodies and non-substrate X-X-Pro- oligopeptides ascertained by capillary electrophoresis.

Dipeptidyl peptidase IV (DP IV)-catalyzed hydrolysis of the NH2-X-Pro-containing N-terminal dodecapeptide of IL-2 was studied using free zone capillary electrophoresis as an alternative peptidase assay. In contrast to the conventional DP IV substrate glycyl-prolyl-p-nitroanilide (Gly-Pro-pNA), the hydrolysis of this peptide by DP IV was found to be significantly inhibited by anti-DP IV antibodies. Inhibition of DP IV was also observed with a number of non-substrate oligopeptides containing an N-terminal X-X-Pro- structure, including the HIV Tat protein. For Met-IL-2(1-6), we determined a competitive inhibition with an inhibition constant of ca. 100 microM.