Gene/Protein Disease Symptom Drug Enzyme Compound
Pivot Concepts:   Target Concepts:
Query: EC:3.4.21.6 (thromboplastin)
 13,278 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

Factor V appears to be a procofactor with, at best, 1/400 the activity of fully activated Factor V (Factor Va). The proteolytic conversion of Factor V to Factor Va is catalyzed by thrombin. However, since Factor Va activity is required for thrombin generation, the initial participation of Factor V in the expression of prothrombinase activity is not well understood. In the present study, the activation of Factor V by Factor Xa has been investigated. Cofactor activation was assessed by monitoring the conversion of prethrombin-1 to thrombin in the presence of 5-dimethylamino-naphthalene-1-sulfonylarginine-N-(3-ethyl-1,5-pentanediyl)amide (DAPA). The DAPA not only provided a fluorescent signal for the formation of thrombin, but also attenuated the feedback activation of Factor V by thrombin. Trace quantities of Factor Va were removed from the Factor V preparations by immunoadsorption with immobilized murine monoclonal antibodies selective for Factor Va. The incubation of Factor V with Factor Xa in the presence of phosphatidylcholine/phosphatidylserine vesicles, CaCl2, and DAPA resulted in a time-dependent increase in cofactor activity. Phosphatidylcholine/phosphatidylserine vesicles were not absolutely required, but the rate of Factor V activation was significantly enhanced by inclusion of the vesicles. The activation was absolutely dependent upon Factor Xa and was eliminated by immunoadsorption of the Factor Xa preparation with a murine anti-Factor X (Xa) monoclonal antibody coupled to agarose. The activation was not affected by immunoadsorption of the Factor Xa and Factor V preparations with burro polyclonal anti-prothrombin IgG. Most of the products of the Factor Xa activation of Factor V differ from the products derived by the thrombin-catalyzed activation of the procofactor. The results demonstrate that Factor Xa catalyzes the activation of Factor V. Furthermore, these studies suggest that the Factor Xa activation of Factor V may be responsible for the advent of early prothrombinase activity.
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PMID:The factor Xa-catalyzed activation of factor V. 664 60

Anticoagulant activities against both the extrinsic and intrinsic coagulation pathways were identified in the saliva of partially fed female lone star ticks, Amblyomma americanum (L.). The activities of factor Xa and thrombin in the common pathway of the coagulation cascade were inhibited by tick saliva. The greatest anticoagulant activities were found in the saliva of ticks weighing more than 200 mg. The anticoagulant activities in tick saliva could be detected without preincubation of tick saliva with sheep plasma, but preincubation significantly increased the activities. Tick saliva anticoagulant activities were abolished by boiling for 15 min or being treated with trypsin for 1 hr. Phosphatidylcholine (3 mM) and phospholipase A2 inhibitor oleyloxyethyl phosphorylcholine (0.2 mM) did not affect the anticoagulant activities significantly, suggesting that the phospholipase A2 activity found in tick saliva does not contribute to the anticoagulant activities. Size exclusion high performance liquid chromatography revealed that the molecular weights of the anticoagulant activities were approximately 16,000 D. The anticoagulant activities in tick saliva are believed to play an important role in facilitating tick feeding by helping overcome the host hemostatic system.
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PMID:Identification and characterization of anticoagulant activities in the saliva of the lone star tick, Amblyomma americanum (L.). 905 94