Identification of cell surface dipeptidylpeptidase IV in human fibroblasts

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Abstract
An antigen with dipeptidylpeptidase IV activity was identified at the surface of normal human fibroblasts. Hydrophobic interaction electrophoresis in phenyl-Sepharose revealed that the enzyme contained a hydrophobic domain, while lactoperoxidase-catalyzed iodination with 125I of living cells indicated that the protein was located at the cell surface. Crossed immunoelectrophoresis with specific antibodies of acid-extracted or papain-treated cells showed a shift of the dipeptidylpeptidase IV peak to a faster mobility. The molecular properties of the fibroblast enzyme were clearly different from those described for dipeptidylpeptidase IV from other tissues and species. Fibroblast dipeptidylpeptidase IV contained 2 different disulfide-linked subunits, of apparent MW values 125,000 and 135,000 (denatured and reduced). In gel filtration, an MW of about 400,000 was observed for the unreduced molecule. The enzymic properties of fibroblast dipeptidylpeptidase IV were very similar to those of the well-characterized pig kidney enzyme. Activity towards glycyl-L-prolyl-.beta.-naphthylamide was inhibited 50% by 0.023 mM-DFP. L-Alanyl-L-alanyl-.beta.-naphthylamide was hydrolyzed 10-times more slowly than glycyl-L-prolyl-.beta.-naphthylamide.