Ca2+-mediated association of glycoprotein G (thrombinsensitive protein, thrombospondin) with human platelets

J Biol Chem. 1980 Dec 25;255(24):11629-32.


Washed human platelets suspended in buffers containing either 1.8 mM Ca2+ and 0.49 mM Mg2+ or 1 mM EDTA were treated with human alpha-thrombin to induce secretion. Glycoprotein G, a major glycoprotein in alpha-granules, was quantitatively secreted from platelets activated in the EDTA-containing buffer but remained with the platelet in the presence of Ca2+ and Mg2+. Addition of Ca2+ to the platelets that were activated in the presence of EDTA caused glycoprotein G to bind to platelets. To determine if glycoprotein G is expressed on the membrane surface of the activated platelet, platelets were rapidly labeled by a method employing lactoperoxidase-catalyzed iodination. Although glycoprotein G was barely detected on the surface of unstimulated platelets, labveling 1 min after thrombin treatment showed that glycoprotein G rapidly became one of the prominent surface proteins. These findings show that an alpha-granule protein, glycoprotein G, is one of the major glycoproteins on the membrane surface of thrombin-activated platelets and that its binding is dependent on divalent cations.

Publication types

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

MeSH terms

  • Adult
  • Blood Platelets / metabolism*
  • Calcium / pharmacology*
  • Edetic Acid / pharmacology
  • Glycoproteins / blood*
  • Humans
  • Magnesium / pharmacology
  • Molecular Weight
  • Platelet Aggregation
  • Protein Binding
  • Thrombin
  • Thrombospondins


  • Glycoproteins
  • Thrombospondins
  • Edetic Acid
  • Thrombin
  • Magnesium
  • Calcium