A family of proteinase-activated receptors that are specific for THROMBIN. They are found primarily on PLATELETS and on ENDOTHELIAL CELLS. Activation of thrombin receptors occurs through the proteolytic action of THROMBIN, which cleaves the N-terminal peptide from the receptor to reveal a new N-terminal peptide that is a cryptic ligand for the receptor. The receptors signal through HETEROTRIMERIC GTP-BINDING PROTEINS. Small synthetic peptides that contain the unmasked N-terminal peptide sequence can also activate the receptor in the absence of proteolytic activity.
Clotting time of PLASMA mixed with a THROMBIN solution. It is a measure of the conversion of FIBRINOGEN to FIBRIN, which is prolonged by AFIBRINOGENEMIA, abnormal fibrinogen, or the presence of inhibitory substances, e.g., fibrin-fibrinogen degradation products, or HEPARIN. BATROXOBIN, a thrombin-like enzyme unaffected by the presence of heparin, may be used in place of thrombin.
Single-chain polypeptides of about 65 amino acids (7 kDa) from LEECHES that have a neutral hydrophobic N terminus, an acidic hydrophilic C terminus, and a compact, hydrophobic core region. Recombinant hirudins lack tyr-63 sulfation and are referred to as 'desulfato-hirudins'. They form a stable non-covalent complex with ALPHA-THROMBIN, thereby abolishing its ability to cleave FIBRINOGEN.
A thrombin receptor subtype that couples to HETEROTRIMERIC GTP-BINDING PROTEINS resulting in the activation of a variety of signaling mechanisms including decreased intracellular CYCLIC AMP, increased TYPE C PHOSPHOLIPASES and increased PHOSPHOLIPASE A2.
Non-nucleated disk-shaped cells formed in the megakaryocyte and found in the blood of all mammals. They are mainly involved in blood coagulation.
Two small peptide chains removed from the N-terminal segment of the alpha chains of fibrinogen by the action of thrombin during the blood coagulation process. Each peptide chain contains 18 amino acid residues. In vivo, fibrinopeptide A is used as a marker to determine the rate of conversion of fibrinogen to fibrin by thrombin.
Agents acting to arrest the flow of blood. Absorbable hemostatics arrest bleeding either by the formation of an artificial clot or by providing a mechanical matrix that facilitates clotting when applied directly to the bleeding surface. These agents function more at the capillary level and are not effective at stemming arterial or venous bleeding under any significant intravascular pressure.
Heparin Cofactor II
The attachment of PLATELETS to one another. This clumping together can be induced by a number of agents (e.g., THROMBIN; COLLAGEN) and is part of the mechanism leading to the formation of a THROMBUS.
Plasma glycoprotein clotted by thrombin, composed of a dimer of three non-identical pairs of polypeptide chains (alpha, beta, gamma) held together by disulfide bonds. Fibrinogen clotting is a sol-gel change involving complex molecular arrangements: whereas fibrinogen is cleaved by thrombin to form polypeptides A and B, the proteolytic action of other enzymes yields different fibrinogen degradation products.
A highly acidic mucopolysaccharide formed of equal parts of sulfated D-glucosamine and D-glucuronic acid with sulfaminic bridges. The molecular weight ranges from six to twenty thousand. Heparin occurs in and is obtained from liver, lung, mast cells, etc., of vertebrates. Its function is unknown, but it is used to prevent blood clotting in vivo and vitro, in the form of many different salts.
Partial Thromboplastin Time
The time required for the appearance of FIBRIN strands following the mixing of PLASMA with phospholipid platelet substitute (e.g., crude cephalins, soybean phosphatides). It is a test of the intrinsic pathway (factors VIII, IX, XI, and XII) and the common pathway (fibrinogen, prothrombin, factors V and X) of BLOOD COAGULATION. It is used as a screening test and to monitor HEPARIN therapy.
Blood Coagulation Factors
Endogenous substances, usually proteins, that are involved in the blood coagulation process.
Partial proteins formed by partial hydrolysis of complete proteins or generated through PROTEIN ENGINEERING techniques.
Blood-coagulation factor VIII. Antihemophilic factor that is part of the factor VIII/von Willebrand factor complex. Factor VIII is produced in the liver and acts in the intrinsic pathway of blood coagulation. It serves as a cofactor in factor X activation and this action is markedly enhanced by small amounts of thrombin.
Use of HIRUDINS as an anticoagulant in the treatment of cardiological and hematological disorders.
The process which spontaneously arrests the flow of BLOOD from vessels carrying blood under pressure. It is accomplished by contraction of the vessels, adhesion and aggregation of formed blood elements (eg. ERYTHROCYTE AGGREGATION), and the process of BLOOD COAGULATION.
Amino Acid Sequence
Molecular Sequence Data
Descriptions of specific amino acid, carbohydrate, or nucleotide sequences which have appeared in the published literature and/or are deposited in and maintained by databanks such as GENBANK, European Molecular Biology Laboratory (EMBL), National Biomedical Research Foundation (NBRF), or other sequence repositories.
Receptors, Cell Surface
Cell surface proteins that bind signalling molecules external to the cell with high affinity and convert this extracellular event into one or more intracellular signals that alter the behavior of the target cell (From Alberts, Molecular Biology of the Cell, 2nd ed, pp693-5). Cell surface receptors, unlike enzymes, do not chemically alter their ligands.
Platelet Glycoprotein GPIb-IX Complex
Platelet membrane glycoprotein complex essential for normal platelet adhesion and clot formation at sites of vascular injury. It is composed of three polypeptides, GPIb alpha, GPIb beta, and GPIX. Glycoprotein Ib functions as a receptor for von Willebrand factor and for thrombin. Congenital deficiency of the GPIb-IX complex results in Bernard-Soulier syndrome. The platelet glycoprotein GPV associates with GPIb-IX and is also absent in Bernard-Soulier syndrome.
The natural enzymatic dissolution of FIBRIN.
A class of receptors that are activated by the action of PROTEINASES. The most notable examples are the THROMBIN RECEPTORS. The receptors contain cryptic ligands that are exposed upon the selective proteolysis of specific N-terminal cleavage sites.
A metallocarboxypeptidase that removes C-terminal lysine and arginine from biologically active peptides and proteins thereby regulating their activity. It is a zinc enzyme with no preference shown for lysine over arginine. Pro-carboxypeptidase U in human plasma is activated by thrombin or plasmin during clotting to form the unstable carboxypeptidase U.
A basic element found in nearly all organized tissues. It is a member of the alkaline earth family of metals with the atomic symbol Ca, atomic number 20, and atomic weight 40. Calcium is the most abundant mineral in the body and combines with phosphorus to form calcium phosphate in the bones and teeth. It is essential for the normal functioning of nerves and muscles and plays a role in blood coagulation (as factor IV) and in many enzymatic processes.
A product of the lysis of plasminogen (profibrinolysin) by PLASMINOGEN activators. It is composed of two polypeptide chains, light (B) and heavy (A), with a molecular weight of 75,000. It is the major proteolytic enzyme involved in blood clot retraction or the lysis of fibrin and quickly inactivated by antiplasmins.
A G-protein-coupled, proteinase-activated receptor that is expressed in a variety of tissues including ENDOTHELIUM; LEUKOCYTES; and the GASTROINTESTINAL TRACT. The receptor is activated by TRYPSIN, which cleaves off the N-terminal peptide from the receptor. The new N-terminal peptide is a cryptic ligand for the receptor. The uncleaved receptor can also be activated by the N-terminal peptide present on the activated THROMBIN RECEPTOR and by small synthetic peptides that contain the unmasked N-terminal sequence.
Platelet Membrane Glycoproteins
A proteolytic enzyme obtained from the venom of fer-de-lance (Bothrops atrox). It is used as a plasma clotting agent for fibrinogen and for the detection of fibrinogen degradation products. The presence of heparin does not interfere with the clotting test. Hemocoagulase is a mixture containing batroxobin and factor X activator. EC 3.4.21.-.
An enzyme fraction from the venom of the Malayan pit viper, Agkistrodon rhodostoma. It catalyzes the hydrolysis of a number of amino acid esters and a limited proteolysis of fibrinogen. It is used clinically to produce controlled defibrination in patients requiring anticoagulant therapy. EC 3.4.21.-.
Fibrinogens which have a functional defect as the result of one or more amino acid substitutions in the amino acid sequence of normal fibrinogen. Abnormalities of the fibrinogen molecule may impair any of the major steps involved in the conversion of fibrinogen into stabilized fibrin, such as cleavage of the fibrinopeptides by thrombin, polymerization and cross-linking of fibrin. The resulting dysfibrinogenemias can be clinically silent or can be associated with bleeding, thrombosis or defective wound healing.
Amino Acid Chloromethyl Ketones
Derivatives of phosphatidic acids in which the phosphoric acid is bound in ester linkage to the hexahydroxy alcohol, myo-inositol. Complete hydrolysis yields 1 mole of glycerol, phosphoric acid, myo-inositol, and 2 moles of fatty acids.
Dose-Response Relationship, Drug
Platelet Aggregation Inhibitors
Drugs or agents which antagonize or impair any mechanism leading to blood platelet aggregation, whether during the phases of activation and shape change or following the dense-granule release reaction and stimulation of the prostaglandin-thromboxane system.
Fibrin Fibrinogen Degradation Products
An endogenous family of proteins belonging to the serpin superfamily that neutralizes the action of thrombin. Six naturally occurring antithrombins have been identified and are designated by Roman numerals I to VI. Of these, Antithrombin I (see FIBRIN) and ANTITHROMBIN III appear to be of major importance.
Blood Coagulation Disorders
Hemorrhagic and thrombotic disorders that occur as a consequence of abnormalities in blood coagulation due to a variety of factors such as COAGULATION PROTEIN DISORDERS; BLOOD PLATELET DISORDERS; BLOOD PROTEIN DISORDERS or nutritional conditions.
Fibrinolysin or agents that convert plasminogen to FIBRINOLYSIN.
A serine endopeptidase that is formed from TRYPSINOGEN in the pancreas. It is converted into its active form by ENTEROPEPTIDASE in the small intestine. It catalyzes hydrolysis of the carboxyl group of either arginine or lysine. EC 184.108.40.206.
The intracellular transfer of information (biological activation/inhibition) through a signal pathway. In each signal transduction system, an activation/inhibition signal from a biologically active molecule (hormone, neurotransmitter) is mediated via the coupling of a receptor/enzyme to a second messenger system or to an ion channel. Signal transduction plays an important role in activating cellular functions, cell differentiation, and cell proliferation. Examples of signal transduction systems are the GAMMA-AMINOBUTYRIC ACID-postsynaptic receptor-calcium ion channel system, the receptor-mediated T-cell activation pathway, and the receptor-mediated activation of phospholipases. Those coupled to membrane depolarization or intracellular release of calcium include the receptor-mediated activation of cytotoxic functions in granulocytes and the synaptic potentiation of protein kinase activation. Some signal transduction pathways may be part of larger signal transduction pathways; for example, protein kinase activation is part of the platelet activation signal pathway.