User:Simoncaulton/sandbox: Difference between revisions
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[[File:Contact system.svg|400px|right|The two arms of the contact system.]] |
[[File:Contact system.svg|400px|right|The two arms of the contact system.]] |
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The '''contact activation system''' or '''CAS''' involves three proteins: [[factor XII]] (FXII), [[prekallikrein]] (PK) and [[kininogen|high molecular weight kiningogen]] (HK). FXII and PK are [[protease]]s and HK is a non-enzymatic co-factor. The CAS can activate the [[ |
The '''contact activation system''' or '''CAS''' involves three proteins: [[factor XII]] (FXII), [[prekallikrein]] (PK) and [[kininogen|high molecular weight kiningogen]] (HK). FXII and PK are [[protease]]s and HK is a non-enzymatic co-factor. The CAS can activate the [[kinin–kallikrein system]] and [[blood coagulation]] through its ability to activate multiple downstream proteins. The CAS is initiated when FXII binds to a surface and reciprocal activation of FXII and PK occurs, forming FXIIa and PKa. FXIIa can initiate the [[coagulation cascade]] by cleaving and activating [[factor XI]] (FXI), which leads to formation of a blood clot. Additionally, the CAS can activate the kinin–kallikrein system. Here, PKa cleaves HK to form cHK, releasing a peptide known as [[bradykinin]] (BK). BK and its derivatives bind to bradykinin receptors [[bradykinin receptor B1|B1]] and [[bradykinin receptor B2|B2]] to mediate [[inflammation]]. |
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==Surfaces== |
==Surfaces== |
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The contact system activates upon FXII's binding to negatively charged surfaces. This is observed routinely |
The contact system activates upon FXII's binding to negatively charged surfaces. This is observed routinely |
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==Phyiological roles== |
==Phyiological roles== |
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Although the contact system can activate FXI and the subsequent clotting cascade, and it is routinely observed to activate coagulation in the presence of medical devices, the actual role of the contact system in normal physiological coagulation remains contentious. This is primarily due to the fact that deficiencies in the contact system proteins FXII, PK and HK do not produce bleeding disorders. FXI deficiency, however, does cause a mild bleeding disorder. |
Although the contact system can activate FXI and the subsequent clotting cascade, and it is routinely observed to activate coagulation in the presence of medical devices, the actual role of the contact system in normal physiological coagulation remains contentious. This is primarily due to the fact that deficiencies in the contact system proteins FXII, PK and HK do not produce bleeding disorders. FXI deficiency, however, does cause a mild bleeding disorder. |
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==Roles in disease== |
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Revision as of 09:48, 31 July 2018
The contact activation system or CAS involves three proteins: factor XII (FXII), prekallikrein (PK) and high molecular weight kiningogen (HK). FXII and PK are proteases and HK is a non-enzymatic co-factor. The CAS can activate the kinin–kallikrein system and blood coagulation through its ability to activate multiple downstream proteins. The CAS is initiated when FXII binds to a surface and reciprocal activation of FXII and PK occurs, forming FXIIa and PKa. FXIIa can initiate the coagulation cascade by cleaving and activating factor XI (FXI), which leads to formation of a blood clot. Additionally, the CAS can activate the kinin–kallikrein system. Here, PKa cleaves HK to form cHK, releasing a peptide known as bradykinin (BK). BK and its derivatives bind to bradykinin receptors B1 and B2 to mediate inflammation.
Surfaces
The contact system activates upon FXII's binding to negatively charged surfaces. This is observed routinely
Phyiological roles
Although the contact system can activate FXI and the subsequent clotting cascade, and it is routinely observed to activate coagulation in the presence of medical devices, the actual role of the contact system in normal physiological coagulation remains contentious. This is primarily due to the fact that deficiencies in the contact system proteins FXII, PK and HK do not produce bleeding disorders. FXI deficiency, however, does cause a mild bleeding disorder.