Structure and Function of Platelet Glycocalicin^[*]

Summary

Present knowledge of the structure and function of platelet glycocalicin is reviewed. Glycocalicin (M,. 150,000) is a glycoprotein component of the outer surface of intact platelets which is released in soluble form following platelet homogenization. Glycocalicin has been purified and shown to inhibit platelet aggregation induced by thrombin or by ristocetin. Thrombin binding activity is associated with the peptide “tail” of the molecule (M_r 45,000), the macroglycopeptide portion (M_r 120,000) being without effect. Glycocalicin and membrane-bound glycoprotein I have been shown to be functionally and immunologically identical. Studies with platelets modified by chymotrypsin, and with platelets from patients with Bemard-Soulier disease and an ill-defined bleeding abnormality show that the amount of thrombin bound is proportional to the total amount of glycocalicin and glycoprotein I present. These results support the concept of a single class of binding site for thrombin in platelets.

^* Presented at the VIth International Congress on Haemostasis and Thrombosis, Philadelphia, U.S.A. Contribution No. 402 from the American Red Cross Blood Research Laboratory. Work reported in this paper has been supported by USPHS Grants HL-20971 and HL-14697 and BRSG S07 RR-05737.

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