PROTEOLYTIC PROCESSING OF NEUROPEPTIDE-Y AND PEPTIDE-YY BY DIPEPTIDYLPEPTIDASE-IV

Neuropeptide Y, peptide YY and pancreatic polypeptide share an evoluti onary conserved proline-rich N-terminal sequence, a structure generall y known to be inert to the attack of common proteinases, but a potenti al target for specialized proline-specific aminopeptidases. Purified h uman dipeptidyl peptidase IV (also termed CD 26) liberated N-terminal Tyr-Pro from both, neuropeptide Y and peptide YY with very high specif ic activities and K-m, values in the micromolar range, but almost no A la-Pro from pancreatic polypeptide. Other proline-specific aminopeptid ases exhibited low (aminopeptidase P, liberation of N-terminal Tyr) or totally no activity (dipeptidyl peptidase II), as was also observed w ith less-specific aminopeptidases (aminopeptidase M, leucine aminopept idase). When human serum was incubated with neuropeptide Y or peptide YY at micro- and nanomolar concentrations, Tyr-Pro was detected as a m etabolite of both peptides. Formation of Tyr-Pro in serum was blocked in the presence of Lys-pyrrolidide and diprotin A (Ile-Pro-Ile), speci fic, competitive inhibitors of dipeptidyl peptidase IV, Incubation of neuropeptide Y or peptide YY with immunocytochemically defined, cultiv ated endothelial cells from human umbilical cord also yielded Tyr-Pro. Dipeptidyl peptidase IV could be immunostained on most endothelial ce lls by a specific antibody. We suggest that dipeptidyl peptidase IV mi ght be involved in the degradation of neuropeptide Y and peptide YY to N-terminal truncated neuropeptide Y(3-36) and peptide YY(3-36). Since specific binding to Y-1, but not to Y-2 subtype of neuropeptide Y/pep tide YY receptors requires intact N- as well as C-termini of neuropept ide Y and peptide YY, removal of their amino-terminal dipeptides by di peptidyl peptidase IV inactivates them for binding to one receptor sub type.