High-molecular-weight kininogen is a binding protein for tissue prokallikrein

Human tissue prokallikrein, a zymogen of the kallikrein-kinin system, circu lates in plasma bound to neutrophils, Because plasma kininogens contribute to the assembly of kinin-generating components on blood cells, these protei ns were assessed for their ability to complex the kallikrein precursor. Usi ng ligand blot and direct binding assays, biotinylated prokallikrein was fo und to bind only to high-molecular-weight kininogen and not to the low-mole cular-weight form. The interaction was specific, reversible, and saturable yielding an estimated dissociation constant K-D = 690 nM and a 1:1 stoichio metry. Specific kininogen binding of tissue prokallikrein also occurred at physiological plasma protein concentrations. These results provide the firs t evidence for a novel function of high-molecular-weight kininogen as a bin ding protein for tissue prokallikrein that could serve to localize the kall ikrein precursor on the neutrophil surface. (C) 2000 Federation of European Biochemical Societies.