Dipeptidyl aminopeptidase IV from porcine pancreas.

Dipeptidyl aminopeptidase IV [EC 3.4.14.5] was purified from the water extract of porcine pancreas acetone powder by a series of column chromatographies on DEAE-Sephadex and gel filtration on Sephadex G-200, and was finally subjected to gel filtration on Toyo-pearl in the presence of 1% deoxycholate. The purified enzyme was homogeneous as judged by disc gel and SDS gel electrophoreses. The enzyme was most active at pH 8.0 with Gly-Pro-beta-naphthylamide (Gly-Pro-2-NNap) as the substrate and hydrolyzed peptide bonds involving the carboxyl group of prolyl residues penultimate to unprotected termini. The enzyme was completely inactivated by diisopropyl phosphorofluoridate (DFP), but only slightly inhibited by phenylmethane sulfonylfluoride (PMSF), SH-blocking reagents and metal chelators. The isoelectric point of the enzyme was 4.8, and the molecular weight was estimated to be 230,000 by gel filtration on Sephadex G-200 and 115,000 by sodium dodecyl sulfate (SDS) gel electrophoresis, suggesting that the enzyme is composed of two identical subunits.