Proline-specific dipeptidyl aminopeptidase from Flavobacterium meningosepticum

A proline-specific dipeptidyl aminopeptidase was highly purified from cell-free extract of Flavobacterium meningosepticum by a series of column chromatographies on DEAE-Sephadex A-50, Sephadex G-150, hydroxyapatite, and a second gel filtration on Sephadex G-150. The enzyme was most active at pH 7.4-7.8 for both Gly-Pro-beta-naphthylamide (Gly-Pro-2-NNap) and Gly-Pro-p-nitroanilide (Gly-Pro-pNA) and was stable between pH 7 and 9.5. The enzyme was markedly inhibited by diisopropylphosphofluoridate (DFP) and mercury ion but not by sulfhydryl-blocking reagents and metal chelators. The molecular weight of the enzyme was about 160,000 as judged by the gel filtration method and the subunit molecular weight was estimated to be 75,000 by sodium dodecyl sulfate (SDS)-gel electrophoresis, suggesting a dimeric form of the native enzyme. The isoelectric point was at pH 9.5. The enzyme hydrolyzed peptides and peptide amides at the carboxyl side of a proline residue penultimate to the amino-terminal amino acid, as did post-proline dipeptidyl aminopeptidases from various mammals. However, antiserum raised against post-proline dipeptidyl aminopeptidase from porcine kidney did not cross-react with the Flavobacterium dipeptidyl aminopeptidase.