Dipeptidyl peptidases 8 and 9: specificity and molecular characterization compared with dipeptidyl peptidase IV

Dipeptidyl peptidases 8 and 9 have been identified as gene members of the S9b family of dipeptidyl peptidases. In the present paper, we report the characterization of recombinant dipeptidyl peptidases 8 and 9 using the baculovirus expression system. We have found that only the full-length variants of the two proteins can be expressed as active peptidases, which are 882 and 892 Amino acids in length for Dipeptidyl Peptidase 8 and 9 respectively. We show further that the purified proteins are active dimers and that they show similar Michaelis-Menten kinetics and substrate specificity. Both cleave the peptide Hormones glucagon-like peptide-1, glucagon-like peptide-2, neuropeptide Y and peptide YY with marked kinetic differences compared with Dipeptidyl Peptidase IV. Inhibition of dipeptidyl peptidases IV, 8 and 9 using the well-known Dipeptidyl Peptidase IV inhibitor valine pyrrolidide resulted in similar K(i) values, indicating that this inhibitor is non-selective for any of the three dipeptidyl peptidases.