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

---

Query: EC:3.4.21.5 (thrombin)
33,306 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

Factor VIII/von Willebrand factor (FVIII/vWF) is a glycoprotein with a molecular weight greater than one-million daltons. Two activities are associated with this large molecule: FVIII procoagulant activity and vWF activity. Incubation of FVIII/vWF with proteolytic enzymes causes rapid inactivation of the FVIII procoagulant activity but has little effect on the vWF activity or antigenicity. In an attempt to gain insight into the structural features required for these two activities, antisera were raised in rabbits to normal, thrombin-inactivated, and plasmin-inactivated FVIII/vWF. All of these proteolytically modified forms of FVIII/vWF cross-reacted with each of the rabbit antisera; each blocked the ability of a human inhibitor to inactivate native active FVIII/vWF. Each of the antisera was a potent inhibitor of vWF activity and inactivated vWF activity at the same titer. The antisera were much less potent inhibitors of FVIII activity than of vWF activity. Antibodies to thrombin-inactivated FVIII/vWF or normal FVIII/vWF had about the same ability to inactivate FVIII procoagulant activity. Surprisingly, those to plasmin-inactivated FVIII/vWF still retained about 50% of this inhibitory capacity. A comparison of the three types of antigens by polyacrylamide gel electrophoresis in sodium dodecyl sulfate-6 M urea demonstrated that the structure of thrombin-inactivated FVIII/vWF was indistinguishable from that of normal FVIII/vWF, while plasmin-inactivated FVII/vWF was completely cleaved to lower molecular weight fragments. Some of the reported variations in the ability of rabbit antibodies to inhibit procoagulant activity may be due to partial degradation of the starting antigen. The retention by FVIII/vWF protein of its immunologic properties even after extensive proteolytic degradation suggests that under nondenaturing conditions, the conformation of the native and degraded molecules are very similar.
...
PMID:Immunologic studies of native and modified human factor VIII/von Willebrand factor. 8 37

The presence of specific Factor VIII/von Willebrand factor (FVIII/vWF) binding sites on human platelets has been demonstrated by using 125I-FVIII/vWF and washed human platelets. Binding is ristocetin-dependent and increases in proportion to the concentration of ristocetin from 0.2 to 1 mg/ml. Binding of 125I-FVIII/vWF to platelets can be competitively inhibited by unlabeled human or bovine FVIII/vWF, but not by human thrombin, fibrinogen, alpha 2-macroglobulin, equine collagen, or a lectin of Ricinus communis. Scatchard analysis of binding data indicated that the dissociation constant of FVIII/vWF receptors is 0.45--0.5 nM. There are 31,000 binding sites per platelet at 1 mg/ml of ristocetin concentration. The optimal pH range for binding is from 7.0 to 7.5. At a concentration of 2 mM, EGTA inhibits 86% of the binding; however, 20 mM of Ca++, Mg++, or EDTA have little effect. Binding sites for FVIII/vWF were found only on platelets, and no significant binding was detected with human erythrocytes or polymorphonuclear leukocytes.
...
PMID:Demonstration and characterization of specific binding sites for factor VIII/von Willebrand factor on human platelets. 10 91

The aggregation of platelets by the antibiotic, ristocetin, requires a plasma cofactor (VIII:vWF) and one or more specific binding sites on the platelet membrane. The interaction between VII:vWF and the platelet was examined using VIII:vWF labelled with 125I. In the presence of ristocetin (1.5 mg/ml), from 70 to 90% of the 125I-VIII:vWF became platelet-bound. By contrast, only 21% was bound with thrombin (2.5 microgram/ml), and 2.2% with buffer alone. Fractionation of the platelets revealed that peak radioactivity was present in the membrane fraction. Treatment of ristocetin-reacted platelets with either chymotrypsin, 100 microgram/ml, or trypsin, 75 microgram/ml, resulted in the partial release of the membrane-bound radioactivity. It is concluded that VIII:vWF binds to the platelet membrane in the presence of ristocetin.
...
PMID:Platelet-binding of the von Willebrand factor. 30 91

When Factor VIII/von Willebrand factor (FVIII/vWF) protein is rechromatographed on 4% agarose in 0.25 M CaCl(2), the protein and vWF activity appear in the void volume, but most of the FVIII procoagulant activity elutes later. Recent evidence suggests that the delayed FVIII procoagulant activity is a proteolytically modified form of FVIII/vWF protein that filters anomalously from agarose in 0.25 M CaCl(2). To test whether or not thrombin is the protease involved, the effect of 0.25 M CaCl(2) on FVIII/vWF and its reaction with thrombin was examined. About 30% of the FVIII procoagulant activity was lost immediately when solutions of FVIII/vWF protein were made 0.25 M in CaCl(2). When FVIII in 0.15 M NaCl was activated with 0.04 U thrombin/ml and then made 0.25 M in CaCl(2), the procoagulant activity of a broad range of FVIII/vWF protein concentrations remained activated for at least 6 h. But, in 0.25 M CaCl(2), the increase in FVIII procoagulant activity in response to thrombin was much more gradual and once activated, the procoagulant activity was stabilized by 0.25 M CaCl(2). When thrombin-activated FVIII/vWF protein was filtered on 4% agarose in 0.15 M NaCl, there was considerable inactivation of FVIII procoagulant activity; however, the procoagulant activity that did remain eluted in the void volume. In contrast, when thrombin-activated FVIII/vWF protein was filtered in 0.25 M CaCl(2), the FVIII procoagulant activity eluted well after the void volume and remained activated for 6 h. The procoagulant peak isolated by filtering nonthrombin-activated FVIII/vWF protein on agarose in 0.25 M CaCl(2) was compared to that isolated from thrombin-activated FVIII/vWF protein. Both procoagulant activity peak proteins had about the same specific vWF activity as the corresponding void volume protein. Before reduction, the sodium dodecyl sulfate gel patterns for the two procoagulant activity peak proteins were the same. After reduction, the gel pattern for the nonthrombin-activated procoagulant activity peak protein contained bands of 195,000, 148,000-120,000, 79,000, 61,000, 51,000, and 18,000 daltons whereas the pattern for the reduced thrombin-activated procoagulant activity peak protein always lacked the higher molecular weight bands, but consistently showed the four lower molecular weight bands to be well resolved. Taken together, these results imply that thrombin generates the FVIII procoagulant activity that is stabilized by 0.25 M CaCl(2) and elutes aberrantly from 4% agarose in that solvent.
...
PMID:Some effects of calcium on the activation of human factor VIII/Von Willebrand factor protein by thrombin. 40 79

We cultivated endothelial cells of human umbilical vein origin in the presence of red blood cells and platelet-rich plasma, and observed the phenomena which occurred in the petri dish under phase contrast microscopy. Many small particles were observed after an overnight incubation. We washed the dish two times, then added thrombin to the dish. The network of thread-like strands appeared within 10 to 20 minutes of the addition, and at the same time the small particles adhered on the surface of the strands, swelled and fused gradually to cover the surface of the strands completely. Within 30 to 60 minutes the network of the strands changed into a capillary-like structure. These phenomena were not observed if we omitted red blood cells or platelet-rich plasma. Studies by transmission electron microscopy revealed that the inner surface of the lumen of the structure was covered with cells. The cells isolated from the lumen by trypsin grew to confluence in the conventional culture medium, and showed vWF antigen on their surface. These observations indicated that the method described is useful for in vitro study of angiogenesis.
...
PMID:Red blood cell and platelet induced differentiation of endothelial cells into capillary-like structure. 128 57

The monoclonal antibody NMC-VIII/10 is a neutralizing antibody which recognizes the Glu1675-Glu1684 sequence of the factor VIII light chain and inhibits factor VIII (FVIII) binding to immobilized von Willebrand factor (vWf). In this study we immunohistochemically determined, using human umbilical cord tissue, whether or not NMC-VIII/10 has an inhibitory effect on FVIII binding to endogenous vWF in endothelial cells. Tissue sections were reacted with purified FVIII followed by peroxidase-conjugated monoclonal antibody (C5) recognizing the 54 kD fragment of the FVIII heavy chain. The labelling pattern of bound FVIII was similar to that of endogenous vWF and appeared as a fine granular deposit in the endothelial cells. Addition of purified vWF completely inhibited the binding of FVIII to endothelial cells. Furthermore, FVIII did not bind to endothelium in the presence of 0.25 M CaCl2, and similarly, thrombin-treated FVIII did not bind to the vascular site. These findings suggested that FVIII was bound to endogenous vWF in the endothelial cells. The binding reaction was completely inhibited by NMC-VIII/10, confirming that the monoclonal antibody recognizes the specific epitope responsible for FVIII binding to endogenous vWF.
...
PMID:A monoclonal antibody (NMC-VIII/10) to factor VIII light chain recognizing Glu1675-Glu1684 inhibits factor VIII binding to endogenous von Willebrand factor in human umbilical vein endothelial cells. 139 Feb 41

Porcine von Willebrand factor (PvWF) induces platelet aggregation which is thought to be responsible for the thrombocytopenia that occurs in haemophilic patients treated with commercial preparations of porcine factor VIII. This study demonstrates that such aggregation can be completely inhibited by a monoclonal antibody against human platelet glycoprotein GPIb and partially inhibited by an antibody directed against platelet GPIIb/IIIa. The interaction of PvWF with GPIb is also demonstrated by the inhibitory effect of purified glycocalycin on aggregation. The binding site of PvWF to GPIb is very close to that of human vWF, since a recombinant peptide blocks the binding of both molecules to GPIb. When platelets are incubated with PvWF, the GPIIb/IIIa receptor is activated and binds fibrinogen. PvWF also binds to GPIIb/IIIa when platelets are stimulated with thrombin, suggesting that the molecule has the same RGD sequence as other adhesive proteins (human vWF, fibrinogen, fibronectin and vitronectin). These findings identify the dual mechanisms responsible for in vivo platelet aggregation induced by PvWF, i.e. binding to GPIb and activation of the GPIIb/IIIa receptor.
...
PMID:Interaction of porcine von Willebrand factor with the platelet glycoproteins Ib and IIb/IIIa complex. 141 6

avWD is a rare entity that is primarily associated with lymphoproliferative disorders, most commonly with multiple myeloma, lymphoma, and the myeloproliferative diseases. Various pathogenetic mechanisms have been postulated. The most commonly seen is antibodies directed against the FVIII complex, resulting in either its accelerated destruction or its accelerated clearance by the reticuloendothelial system. There may be immunoadsorption of the FVIII complexes onto the clones of malignant cells, as has been reported in several cases, or proteolysis may be causing the peripheral destruction of the FVIII complex. Lastly, as seen in hypothyroidism, global decrease in production of the multimers also results in avWD. The treatment, in general, should be aimed at controlling the underlying disorder and at stopping any life-threatening hemorrhage. The treatment includes any or all of the following: DDAVP, cryoprecipitate, FVIII concentrates, extracorporeal immunoadsorption, and chemotherapy as needed to control the underlying disorders. The screening tests that will allow for the detection of the avWD include measurement of the bleeding time, the FVIII:C, FVIII:vWF, and the FVIII:RCoF. FVIII:C inhibitors can be demonstrated by mixing the patient plasma with normal plasma. A normal prothrombin time (PT), activated partial thromboplastin time (APTT), and thrombin time (TT) are expected. Clinically, these patients present with mucosal bleeding, and in avWD tend to have an association with lymphoproliferative malignancies. They tend to be elderly patients with no prior history of bleeding diathesis and to have negative family histories for coagulopathies. Further study of these patients is warranted, because this disorder appears to have a multifactorial etiology. Increasing our understanding of avWD may increase our understanding of congenital vWD, thus allowing us to more effectively treat all patients with von Willebrand's disease.
...
PMID:Acquired von Willebrand's disease. 145 20

Although DDAVP has been shown to be haemostatically efficacious in patients with various congenital or acquired platelet disorders, no reasonable explanation has been found for this effect. We have previously shown DDAVP to increase platelet adhesiveness as measured with a platelet retention test. The aim of the present study was to investigate the mechanism of action responsible for the increased platelet retention in response to DDAVP. Patients with vWD type III and type Ia, severe haemophilia and severe thrombasthenia, as well as healthy controls, were included in the study. The effect of different concentrations of vWF in plasma and platelets was explored, as was the effect on platelet function of apyrase and monoclonal antibodies against GP IIb/IIIa and GP Ib. We found the effect of DDAVP on platelet retention to be unaffected by changes in the plasma concentration of vWF. The enhanced platelet retention after DDAVP is apparently dependent on the presence of platelet-vWF and on a normal function of the GP IIb/IIIa. The effect is not mediated via ADP or thrombin. The platelet-stimulating effect of DDAVP may be one explanation for the positive haemostatic effect in patients with certain platelet disorders.
...
PMID:DDAVP-induced enhancement of platelet retention: its dependence on platelet-von Willebrand factor and the platelet receptor GP IIb/IIIa. 149 98

Alboaggregins (AL-A, AL-B, AL-C) isolated from Trimeresurus albolabris snake venom represent a new family of proteins which bind to platelet glycoprotein Ib (GPIb). These alboaggregins were purified to homogeneity with ion exchange HPLC (Mono-Q column) and hydrophobic HPLC (TSK Phenyl-5PW column). On SDS-polyacrylamide gel electrophoresis, apparent molecular weights of AL-A, AL-B and AL-C were 52 kDa, 26 kDa, and 121 kDa respectively, under nonreducing conditions. Upon reduction, each alboaggregin showed two types of chains with apparent molecular weights in the range of 15-20 kDa. All three alboaggregins agglutinated formalin-fixed platelets. Agglutination activities and binding of labeled alboaggregins to GPIb were specifically inhibited by the monoclonal antibody AK2 which is directed against the 45 kDa N-terminal region on GPIb, but not by monoclonal antibodies against other epitopes on GPIb. 125I-alboaggregin binding to platelets was not altered by the presence of thrombin. Alboaggregins did not bind to GPIIb/IIIa. Alboaggregins were competitive inhibitors for 125I-bovine vWF binding to platelets. Mutual competition studies between AL-A, AL-B and AL-C for the binding of labeled bovine vWF and AL-B to platelets demonstrated that AL-B and AL-C had a significantly higher affinity than AL-A.
...
PMID:Characterization of three alboaggregins purified from Trimeresurus albolabris venom. 150 13


1 2 3 4 5 6 7 8 9 10 Next >>

---