Fibrin in clotting

Such clots—also known as emboli—present a serious hazard by their potential for blocking circulation of blood to vital organs. The considerable research devoted to agents that will lyse the fibrin in clots has led to the development of the clinically useful agent, uj-okinase. This drug is a fibrinolytic proteinaceous enzyme isolated from human urine. The difficulty involved in isolation of significant amounts and the antigenicity of urokinase and a related... 

The a-helix which is found in proteins which need to be extensible as well as strong, such as the keratins present in hair and other epithelial structures, myosin in muscle and fibrin in clotted blood. 

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