Hirudin
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Hirudin is a naturally occurring peptide in the salivary glands of medicinal leeches (Hirudo medicinalis) that has a blood anticoagulant property. This is fundamental for the leeches’ alimentary habit of hematophagy, since it keeps the blood flowing after the initial phlebotomy performed by the worm on the host’s skin.
In 1884, the British physiologist John Berry Haycraft discovered that the leech secreted a powerful anticoagulant, which he named hirudin, though it was not isolated until the 1950s, nor its structure fully determined until 1976.
The effect of hirudin on the blood coagulation biochemical cascade is the inhibition of thrombin. Thrombin is a serine protease, produced from prothrombin, by the action of an enzyme, prothrombinase, in the final states of coagulation. It converts fibrinogen in the blood to fibrin, forming the clot or thrombus.
Hirudin is the most powerful natural inhibitor of thrombin, due to its binding specificity. Therefore, hirudin prevents or dissolves the formation of clots and thrombi (thrombolytic activity), and has therapeutic value in blood coagulation disorders, in the treatment of skin hematomas and of superficial varicose veins, either as an injectable or a topical application cream. In some aspects, hirudin has advantages over more commonly used anticoagulants and thrombolytics, such as heparin, because it doesn’t interfere with other serum proteins and can act also on bound thrombin.
It is difficult to extract large amounts of hirudin from natural sources, so a method for synthesizing it by recombinant biotechnology has been developed. Several other direct thrombin inhibitors are derived chemically from hirudin.
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