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Cerastocytin
Cerastocytin is a thrombin-like serine protease in snake venom.
== Function overview ==
Snake venom contains toxins capable of causing death to the reptile’s prey in many various ways. Most of the toxins fall into one of the two categories:〔(【引用サイトリンク】title=The Reptipage: Snake venom )〕 elapid (mainly neurotoxic) or viperid (mainly hemotoxic) toxins depending on the immediate cause of death.〔(【引用サイトリンク】title=elapid )〕 Elapid snakes cause prey to die from asphyxiation because the dominating neurotoxins inhibit cholinesterase activity, thereby leading to paralysis of all muscles, including the diaphragm.〔Mirajkar, K., More, S., Gadag, J. (2005) Isolation and purification of a neurotoxin from Bungarus caeruleus (common Indian krait) venom: biochemical changes induced by the toxin in rats. J Basic Clin Physiol Pharmacol. 16 (1):37-52.〕 The immediate cause of death after bites of viperid snakes is a sudden drop in blood pressure or stroke as the hemotoxins, mostly prevalent in this type of venom, induce either extensive coagulation or bleeding.〔Bazaa, A. et al. (2005) Snake venomics: Comparative analysis of the venom proteomes of the Tunisian snakes Cerastes cerastes, Cerastes vipera and Macrovipera lebetina. Proteomics 5, 4223–4235〕 While snakes are categorized in this manner, venom of either type may include a number of toxic enzymes involved in neurotoxicity, hemotoxicity, nutrient digestion and other functions necessary to make the prey available for consumption.
While all hemotoxins leading to clot formation induce platelet aggregation, they do so in various ways. For example, botrocetin, found in the venom of Bothrops jararaca, activates von Willebrand factor (vWF) by inducing it to bind to platelet glycoprotein Ib (GPIb) thereby providing the surface for initial platelet aggregation.〔Read MS, Smith SV, Lamb MA, Brinkhous KM (1989) Role of botrocetin in platelet agglutination: formation of an activated complex of botrocetin and von Willebrand factor. Blood. 74(3):1031-5〕 In contrast, cerastocytin and cerastotin (from the venom of Cerastes cerastes), as well as thrombocytin (from Bothrops atrox)〔Niewiarowski S, Kirby EP, Brudzynski TM, Stocker K. (1979) Thrombocytin, a serine protease from Bothrops atrox venom. 2. Interaction with platelets and plasma-clotting factors. Biochemistry. 18(16):3570-7.〕 and many others, are serine proteases that function in a way very similar to thrombin. Like thrombin, these proteases are capable of inducing platelet aggregation, and some even fibrin clot formation, at nanomolar concentrations.
抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』
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