A microscopic method was developed to study the role of platelets in fibrin formation. Perfusion of adhered platelets with plasma under coagulating conditions at a low shear rate (250(-1)) resulted in the assembly of a star-like fibrin network at the platelet surface. The focal fibrin formation on platelets was preceded by rises in cytosolic Ca(2+), morphologic changes, and phosphatidylserine e...

Platelet glycoprotein Ib (GPIb)-binding proteins (GPIb-BPs) from snake venoms are usually C-type lectins, which target specific sites of GPIbalpha and elicit distinct effects on platelets. In the present paper, we report a tetrameric platelet-agglutinating factor (molecular mass 121.1 kDa), termed mucrocetin, purified from the venom of Taiwan habu (Trimeresurus mucrosquamatus ). Mucrocetin is a...

The role of the platelet glycoprotein (GP) Ib-V-IX receptor in thrombin activation of platelets has remained controversial although good evidence suggests that blocking this receptor affects platelet responses to this agonist. The mechanism of expression of procoagulant activity in response to platelet agonists is also still obscure. Here, the binding site for thrombin on GPIb is shown to have ...

We investigated the structural elements in human von Willebrand factor (vWF) that influence binding affinity for platelet glycoprotein (GP) Ib using a dispase-digested vWF fragment as a prototype (residues Leu480/Val481-Gly718 of the vWF subunit; Andrews et al, Biochemistry 28:8326, 1989). The major structural features of this fragment are a large A1-loop formed by an intrachain disulfide bond ...

A soluble radioreceptor assay has been developed to characterize thrombin receptor activities of the human platelet membrane. 125I-Thrombin was added to platelet membranes solubilized in 1% Triton X-100, and thrombin bound to platelet receptors was separated from free thrombin by precipitation with wheat germ agglutinin (WGA) in the presence of alpha 1-acid glycoprotein as carrier. Both high af...

Five novel monoclonal antibodies (mAbs; p0p 1-5) were used to characterize the structural and functional properties and the in vivo expression of the murine GPIb-IX complex (von Willebrand factor receptor). The molecular weights of the subunits are similar to the human homologs: GPIbalpha (150 kd), GPIbbeta (25 kd), and GPIX (25 kd). Activation of platelets with thrombin or PMA predominantly in...

Different types of platelets in various types of plasma were subjected to levels of shear stress that produce irreversible platelet aggregation in normal platelet-rich plasma (PRP). At shear stresses of 90 or 180 dyne/cm2 applied for 30 seconds or five minutes, aggregation was either absent or only transient and reversible using severe von Willebrand's disease (vWD) PRP (less than 1% von Willeb...

Adhesion of platelets to extracellular matrix via von Willebrand factor (vWF) and activation of platelets by thrombin are critical steps in hemostasis. Glycoprotein (GP) V is a component of the GPIb-V-IX complex, the platelet receptor for vWF. GPV is also cleaved by thrombin. Deficiency of GPIb or GPIX results in Bernard-Soulier syndrome (BSS), a bleeding disorder in which platelets are giant a...

Quinidine-induced thrombocytopenia has been associated with both immune complex and autoantibody binding to platelets. In the present study, serum antibody from six of six patients with quindine purpura was shown by immunoblotting to bind to a single platelet membrane protein of mol wt 80,000. This target protein was absent from Bernard-Soulier (BSS) platelets. F(ab)2 prepared from one patient'...