Action of thrombin on surface glycoproteins of human platelets

We labeled surface glycoproteins of human platelets by the neuraminidase-galactose oxidase/borotritiide and the periodate/borotritiide methods. When labeled platelets were treated with 1-nM thrombin, a minor glycoprotein weighing 68,000–85,000-d was lost from the surface, and a soluble glycoprotein weighing 57,000- 68,000-d was found in the supernatant. Treatment of platelets with ADP, collagen, or the calcium ionophore A23187 did not cause loss of the 68,000–85,000-d glycoprotein from platelet surfaces or appearance of the 57,000–68,000-d glycoprotein in the supernatant. However, trace amounts of the intact 68,000–85,000-d glycoprotein were found in the supernatants of platelets that were not treated with thrombin. The numerous effects of thrombin on platelets could be initiated by cleavage and release the thrombin-sensitive glycoprotein.