J. Biol. Chem., Vol. 261, Issue 2, 684-689, 01, 1986
Human protease nexin-I. Further characterization using a highly specific polyclonal antibody
EW Howard and DJ Knauer
We have used purified protease nexin-I (PN-I) from human fibroblasts to
develop a polyclonal antibody that specifically blocks the PN-I- mediated
cellular binding of thrombin and urokinase. Anti-PN-I IgG did not inhibit
the binding of 125I-epidermal growth factor-binding protein to fibroblasts,
which is mediated by protease nexin-II, another cell- secreted, serine
protease inhibitor that is distinct from PN-I. This furthers the belief
that the protease nexins are distinct from one another. In addition, while
anti-PN-I IgG immunoprecipitated PN-I X thrombin complexes, it did not do
so with antithrombin-III X thrombin. Metabolically labeled PN-I was also
immunoprecipitated by IgG, indicating that the protein can be labeled in
vivo. The antibody also recognized primarily one band on Western transfers
of conditioned medium from fibroblast cultures. These results suggest that
anti-PN-I will be useful in probing the physiological role of PN-I as well
as its biosynthesis.