Gene/Protein Disease Symptom Drug Enzyme Compound
Pivot Concepts: Gene/Protein Disease Symptom Drug Enzyme Compound   Target Concepts: Gene/Protein Disease Symptom Drug Enzyme Compound

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Query: EC:3.4.21.6 (thromboplastin)
13,278 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

Human isolated monocytes possess low levels of procoagulant activity, which was stimulated 10-30 fold by brief (2 hr) exposure to 10 micrograms/ml endotoxin. This activity was expressed in normal or factor XII-deficient plasma, but lost in plasma deficient in factors X or VII, indicating that it was due to thromboplastin. The stimulation of monocyte thromboplastin by endotoxin was inhibited in a dose-dependent manner by two phospholipase A2 inhibitors, 4-bromophenacyl bromide and quinacrine, and by two lipoxygenase inhibitors, eicosatetraynoic acid and nordihydroguaiaretic acid. Two cyclooxygenase inhibitors, aspirin and indomethacin, prevented endotoxin-induced increases in thromboxane B2 production but had no effect on thromboplastin production. These results suggest that a component in the sequence of lipid deacylation, arachidonic acid release, and metabolism via lipoxygenase may mediate the stimulation of monocyte thromboplastin activity by endotoxin.
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PMID:Effects of inhibitors of arachidonic acid metabolism on thromboplastin activity in human monocytes. 642 35

A 42-yr-old woman with systemic lupus erythematosus without bleeding diathesis developed a prolonged activated partial thromboplastin time that was not corrected by normal plasma. An inhibitor that acted rapidly and inactivated 0.5 U/ml plasma thromboplastin antecedent (PTA, factor XI) at a 1:200 plasma dilution was demonstrated. In addition to a low titer of PTA (less than 0.01 U/ml), plasma assayed at 20-fold dilution also showed low titers of Hageman (factor XII, 0.02 U/ml), Fletcher (plasma prekallikrein, 0.02 U/ml), and Fitzgerald (high molecular weight kininogen, less than 0.01 U/ml) factors. The titer of these factors, except PTA, returned to normal upon further plasma dilution or upon removal of the inhibitor by protein A adsorption. Thus, the inhibitor appeared to interfere with these clotting factor assays, possibly by inactivating PTA in the substrate plasmas in the test system. Its specificity was further confirmed. The inhibitor did not interfere with surface-induced proteolytic cleavage of Hageman factor. Surface-induced generation of plasma kallikrein activity (amidolysis of H-D-pro-phe-arg-pNa and cold-promoted factor VII activity enhancement) requires only Hageman, Fletcher, and Fitzgerald factors and was normal. Reactions requiring all 4 contact phase factors, including PTA, such as surface-induced generation of plasmin activity (amidolysis of H-D-val-leu-lys-pNa) and activated Christmas factor (factor IXa) activity, were defective. Furthermore, the inhibitor bound to agarose-protein A inactivated and removed PTA selectively from normal plasma. The inhibitor was an IgG-lambda autoantibody that precipitated PTA. The inactivated activated PTA (factor XIa) without the requirement for an additional cofactor. Furthermore, it inhibited surface-induced activation of PTA by interfering with its proteolytic cleavage upon glass surface exposure and with its binding onto the reactive surfaces.
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PMID:A unique precipitating autoantibody against plasma thromboplastin antecedent associated with multiple apparent plasma clotting factor deficiencies in a patient with systemic lupus erythematosus. 642 50

Human factor XII was activated by limited proteolysis with trypsin, and the resulting beta-factor XIIa (Mr = 30,000) was isolated by DEAE-Sephacel column chromatography. The complete amino acid sequence of beta-factor XIIa was then determined on peptides produced by enzymatic digestion with either trypsin, chymotrypsin, or Staphylococcus aureus V8 protease and by chemical cleavage at methionyl and tryptophyl bonds. beta-Factor XIIa is a glycoprotein composed of a heavy chain (243 amino acid residues) and a light chain (9 amino acid residues), and these two chains are held together by a disulfide bond. The carbohydrate is attached to asparagine residue 61 in the heavy chain. The amino acid sequence of the heavy chain shows a high degree of homology to the corresponding regions of other plasma serine proteases, such as plasmin, thrombin, factor IXa and factor Xa, as well as the pancreatic digestive enzymes. These results demonstrate that factor XII is the precursor of a typical serine protease that participates in the coagulation cascade.
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PMID:Amino acid sequence of human beta-factor XIIa. 660 55

Platelet prothrombin-converting activity and factor Xa binding were studied after exposure of human platelet rich plasma (PRP) to various conditions leading to platelet activation. Zymosan resulted in increased platelet-bound C3, enhanced prothrombin-converting activity and increased factor Xa binding. Similar findings were observed with normal platelets resuspended in factor XII-deficient plasma. The combined use of zymosan and thrombin to activate platelets resulted in synergistic prothrombin-converting activity and factor Xa binding. In contrast, no synergism was obtained with the concomitant use of zymosan and collagen, suggesting that collagen and zymosan share the same pathway for platelet activation. Heterologous antibody to factor V completely inhibited the platelet prothrombin-converting activity for all modes of platelet activation, indicating that this activity is mediated by factor V.
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PMID:Enhanced prothrombin-converting activity and factor Xa binding of platelets activated by the alternative complement pathway. 661 Apr 38

Fibrin clots have been detected at sites of inflammation, and kinins have been implicated as mediators of the vascular phenomena of acute inflammation, systemic shock, and disseminated intravascular coagulation. It is now reported that both negatively and positively charged asbestos fibers shorten the partial thromboplastin time of human plasma, indicating coagulation of the plasma. A sample containing short (less than 5 micron in length) chrysotile fibers is ineffective. Only the negatively charged amphiboles (crocidolite and amosite) are able to activate factor XII (Hageman factor). This particular effect of the amphiboles is enhanced by high molecular weight kininogen and leads to kinin formation.
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PMID:Asbestos fibers, plasma and inflammation. 664 59

Recent studies on the mechanism of initiation and regulation of blood coagulation are reviewed. In the intrinsic blood coagulation pathway, factor XII, prekallikrein (or factor XI) and high molecular weight kininogen from a complex on an anionic surface, such as exposed subendothelium at the site of vascular trauma. In complex, zymogen factor XII activates prekallikrein (or factor XI) by limited proteolysis to initiate the coagulation cascade. A similar initiating mechanism may be operative in the extrinsic pathway, where zymogen factor VII, complexed with a lipoprotein (tissue factor) and calcium ions, converts factor X to factor Xa. Factor Xa converts prothrombin to thrombin which converts soluble fibrinogen to an insoluble fibrin network which physically arrests the flow of blood from the damaged vasculature. In addition, thrombin converts protein C to activated protein C. Activated protein C functions as a negative regulator in the coagulation process by degrading factor VIIIa and factor Va.
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PMID:Enzymological aspects of blood coagulation. 668 3

Activated partial thromboplastin time (APTT) was examined in Brown Norway (B/N) Katholiek rat, which was previously reported as high molecular weight kininogen deficient. APTT of B/N Katholiek was prolonged to 35 sec in comparison with B/N Kitasato and SD rat, showing APTT of 22-24 sec. The mixture of B/N Katholiek plasma and B/N Kitasato plasma (1:1) showed normal APTT value. B/N Katholiek plasma corrected the abnormally prolonged human coagulation factor deficient plasmas, such as XI, XII and prekallikrein deficient plasmas, while it did not correct the APTT of HMW kininogen deficient, Fitzgerald plasma. Intravenous injection of bromelain, which was previously reported to produce prolonged hypotension through the activation of factor XII to release bradykinin, induced slight effect in Katholiek rat, while in Kitasato rat it showed prolonged hypotension in similar degree as SD rat. Contents of coagulation factors in B/N Katholiek thus measured as well as the values of prekallikrein and HMW kininogen previously reported were summarized and suggested that B/N Katholiek rat could be similar deficiency as Fitzgerald trait.
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PMID:Prolonged activated partial thromboplastin time and deficiency of high molecular weight kininogen in brown Norway rat mutant (Katholiek strain). 671 Apr 38

A patient with factor XII deficiency, gout, and angioimmunoblastic lymphadenopathy (AIL) was seen initially for an acute myocardial infarction, gout, and unexplained urticaria. The patient eventually was found to have AIL and a prolonged partial thromboplastin time. There was no evidence of a circulating anticoagulant. A factor XII deficiency (Hageman factor) was discovered. The coexistence of a factor XII deficiency, AIL, and gout in the same person raises some interesting questions regarding the basic mechanisms of the inflammatory process.
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PMID:Factor XII deficiency in a man with gout and angioimmunoblastic lymphadenopathy. 673 12

Incubation of normal human plasma with low amounts of sulfatides resulted in the initiation of intrinsic coagulation and the appearance of kallikrein activity. The optimal initiation of procoagulant and kallikrein amidolytic activity was dependent on the presence of factor XII, high molecular weight kininogen, and prekallikrein. Since the activated partial thromboplastin clotting times in prekallikrein-deficient plasma approach normal values upon prolonged incubation with kaolin, this phenomenon of autocorrection was studied and found to be even more pronounced in the presence of sulfatides. Autocorrection was essentially completed in 5 min in the presence of sulfatides, whereas a preincubation of 15-20 min was required in the presence of kaolin. The limited proteolysis of 125I-factor XII in plasma during incubation with activating material or during clotting was determined. Cleavage of factor XII was more rapid and more extensive in the presence of sulfatides than in the presence of kaolin. In prekallikrein-deficient plasma, factor XII cleavage was completed within 5 min in the presence of sulfatides and within 15 min in the presence of kaolin. Thus, the appearance of factor-XII-dependent coagulant activity correlates with the limited proteolysis of factor XII when normal or prekallikrein-deficient plasma is activated by sulfatides or kaolin.
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PMID:Properties of sulfatides in factor-XII-dependent contact activation. 691 2

Factor XII plasma levels were investigated with several methods in patients with hemophilia A and B and von Willebrand syndrome. There seem to be some families with hemophilia A or von Willebrand syndrome, who have an additional, congenital, partial lack of factor XII (Hageman factor). The mode of inheritance is independent of the other coagulation disorder. Frequently, the first indication of an additional factor XII deficiency is the disproportionate prolongation of the activated partial thromboplastin time (PTT) as regards the factor VIII level. The average factor XII level in patients with hemophilia A and von Willebrand syndrome is significantly lower than in normal subjects or patients with hemophilia B. It cannot be excluded that the frequently low levels of factor XII in patients with severe hemophilia are acquired and probably due to liver cell damage.
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PMID:Additional factor XII (Hageman factor) deficiency in hemophilia A and in von Willebrand syndrome. 697 68


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