Identification of the Bile Canalicular Cell Surface Molecule Gp110 As the Ectopeptidase Dipeptidyl Peptidase Iv: An Analysis by Tissue Distribution, Purification And N –Terminal Amino Acid Sequence

Abstract

This paper describes the tissue distribution, purification and N–terminal amino acid sequence of the bile canalicular cell surface molecule dipeptidyl peptidase IV. Immunoperoxidase staining of cryostat sections of rat liver with a monoclonal antibody, Medical Research Council OX–61, indicated specific binding to hepatocyte bile canalicular domains and brush borders of bile ducts. Additional staining was seen in other epithelial brush borders (small intestine, kidney, colon, pancreatic duct); acinar structures in salivary glands; endothelial structures and T cell areas in thymus, spleen and lymph node. The tissue distribution suggested that monoclonal antibody OX–61 binds to the ectoenzyme dipeptidyl peptidase IV. This was confirmed by depletion of dipeptidyl peptidase IV activity from tissue homogenates by monoclonal antibody OX–61 coupled to Sepharose. The molecule recognized by OX–61 was then purified from liver and kidney by monoclonal antibody affinity chromatography. The molecule had a molecular weight of 110 kD under reducing conditions. The purified molecule was subsequently analyzed for amino acid composition and N–terminal amino acid sequence. Thirty–one N–terminal amino acids were sequenced and indicated identity with part of the predicted N–terminus of the previously cloned bile canalicular molecule GP110. On review, other similarities between dipeptidyl peptidase IV and GP110 were detected: molecular weight, deglycosylated from and metabolic half–life. Finally, the recent cloning of dipeptidyl peptidase IV permitted a comparison between the molecule recognized by monoclonal antibody OX–61, GP110 and dipeptidyl peptidase IV. It is concluded that these three molecules are almost certainly identical.(HEPATOLOGY 1990; 11:534:544.)