Tenase

Activated on surface of activated platelets by tenase complex (Ca, factors Villa and IXa) and by factor Vila in presence of tissue factor and Ca. ... 

Factor XIa in the presence of activates factor IX (55 kDa, a zymogen containing vitamin K-dependent y-carboxyglutamate [Gla] residues see Chapter 45), to the serine protease, factor IXa. This in turn cleaves an Arg-Ile bond in factor X (56 kDa) to produce the two-chain serine protease, factor Xa. This latter reaction requires the assembly of components, called the tenase... 

Fig. 2. Generation of tenase and prothrombin complexes. PPL represents the anionic phospholipid surface provided by the platelets (platelet phospholipid). Cleavage of prothrombin by the prothrombinase complex results in the formation of thrombin and the release of a small fragment called prothrombin fragment 1.2 (PFI.2).

Platelet membrane phosphatidylserine is critical to the formation of the tenase complex since on its surface activated factor VIII (Villa) generates a high-afflnity binding site for activated factor IX (IXa) in the presence of calcium. Subsequently, this complex activates factor X (2, 13). Platelet membrane phosphatidylserine similarly anchors activated factor V (Va), favoring the calcium-dependent binding of activated factor X (Xa). The prothrombinase complex is generated on the surface of the anionic platelet membrane phosphatidylserine when factor Va binds prothrombin. The prothrombinase complex cleaves prothrombin to produce thrombin, which has a multifunctional role (14). 

On surface of platelet membrane phospholipid, phosphatidyl serine forms tenase and prothrombinase complexes... 

Sheehan JP, Lan H-C. Phosphorothioate oligonucleotides inhibit the intrinsic tenase complex. Blood 1998 92(5) 1617-25. 

Factor VEIa is the co-factor of factor IXa together they form the tenase complex which activates factor X, and so the cycle continues. 

The tenase complex is formed by the activated forms of the blood coagulation factors VIE and IX. It forms on a phospholipid surface in the presence of calcium and is responsible for the activation of factor X. Tenase is a contraction of ten and the suffix -ase , used for enzymes... 

PrekaUikrein is converted to kaUrkrem and factor XII is activated to Xlla. Factor Xlla activates Xl-XIa, which activates factor IX, which together with its co-factor Villa forms the tenase complex, resniting in activation of factor X. The minor role that the contact activation pathway has in initiating clot formation can he Ulnstrated hy the fact that patients with severe deficiencies of factor Xn, kininogen and prekaUikrein do not exhibit a bleeding disorder. 

Following activation by the contact factor or TF pathways, the coagulation cascade is maintained in a prothrombotic state by the continued activation of factors VIII and IX to form the tenase complex, until it is down-regulated by the anticoagulant pathways (see Section 11.9). 

Calcium and phospholipid. Required for the tenase and prothrombinase complexes to function. Calcium mediates the binding of the complexes via the terminal y-carboxy residues on factor Xa and factor IXa to the phospholipid surfaces expressed by platelets, as well as those procoagulant microparticles or microvesicles shed from them. 

Tissue factor is a membrane protein found in organs and surrounding the vasculature. Tissue factor is exposed to blood as a consequence of vessel wall damage or inflammatory cytokine release from vascular cells or monocytes. Coagulation is initiated when factor Vila binds to exposed or expressed tissue factor (see Fig. 100-2). The factor Vlla-tissue factor complex activates factors IX and X. Activated platelets form complexes with factor IXa-factor Vnia (tenase) and factor... 

Xa-factor Va (prothrombinase). Tenase activates factor X and pro-thrombinase converts prothrombin to thrombin. Thrombin activates platelets and catalyzes the conversion of fibrinogen to fibrin. Thrombin also amplifies coagulation by activating factors V, VIII, and XL... 

Tenase . [Solvay Enzymes] Alpha-amylase enzyme for sta liquefaction. 

Temik oxime. See Aldicarb oxime TEN. SeeTriethylamine Tenase 120C/, Tenase L-340, Tenase L-1200. See Amylase... 

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