Proteolysis of Platelet Glycoprotein Ib by Plasmin Is Facilitated by Plasmin Lysine-Binding Regions

Blood. 1986 Dec;68(6):1280-4.


We have characterized the effects of plasmin on glycoprotein Ib (GpIb), a platelet membrane receptor for von Willebrand factor (vWF), and on glycocalicin, a fragment of the alpha chain of GpIb that contains the vWF-binding region. The addition of 4.5 X 10(-7) mol/L plasmin to washed platelets caused a time-dependent decrease in ristocetin-induced, vWF-dependent platelet agglutination. epsilon-Aminocaproic acid (EACA) inhibited plasmin release of glycocalicin-related antigen from washed platelets and preserved vWF-dependent platelet agglutination, thus indicating that the lysine-binding sites on plasmin facilitated its degradation of GpIb. To demonstrate a direct interaction between plasmin and the vWF-binding region of GpIb we incubated purified glycocalicin with plasmin. Plasmin degraded the glycocalicin into two small carbohydrate-poor peptides and into a larger carbohydrate-rich fragment. EACA was able to inhibit plasmin-mediated degradation of glycocalicin in a concentration-dependent fashion. These studies indicated that plasmin degradation of GpIb was due to a direct interaction between plasmin and GpIb and that this effect was mediated by the lysine-binding region of the plasmin molecule.

Publication types

  • Research Support, Non-U.S. Gov't
  • Research Support, U.S. Gov't, P.H.S.

MeSH terms

  • Aminocaproates / pharmacology
  • Binding Sites
  • Blood Platelets / metabolism*
  • Fibrinolysin / metabolism*
  • Humans
  • Lysine / metabolism
  • Platelet Aggregation
  • Platelet Glycoprotein GPIb-IX Complex*
  • Platelet Membrane Glycoproteins / metabolism*
  • Ristocetin / metabolism
  • von Willebrand Factor / metabolism


  • Aminocaproates
  • Platelet Glycoprotein GPIb-IX Complex
  • Platelet Membrane Glycoproteins
  • glycocalicin
  • von Willebrand Factor
  • Ristocetin
  • Fibrinolysin
  • Lysine