Entomological Evolution: Substance H Introduc

Various insects rely on human blood for survival. Feeding behaviors typically involve puncture of the epidermis. Blood withdrawal is facilitated by injecting the host with various salivary agents. One of these, Substance H, has been reported to have both anticoagulant and antithrombotic activities. This has led researchers to conclude that Substance H could be used to treat thromboembolic disease.

Normal blood flow occurs within a high-pressure, closed circulatory system. The hemostatic process involves both cellular and aqueous phases, and provides the host with a defense against injury and blood loss. The first step in the overall reaction consists of platelet adhesion and aggregation to form a hemostatic plug. Second, with blood coagulation, fibrinogen polymerization occurs. Ultimately, the platelet plug is replaced with a chemically stable fibrin clot.

Platelets essentially consist cytoplasmic fragments of megakaryocytes. These small anucleate cells circulate for about 10 days before being removed by the spleen. The cells have two primary functions which are essential for normal hemostasis. For one, platelet aggregations form a physical barrier to blood loss at sites of vascular injury. In addition, platelet surface phospholipids accelerate blood coagulation.

In their unactivated state, platelets are disc-shaped. With some deterioration in the circulation, however,

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ation of an ester linkage between the active center serine hydroxyl group of the protease and the a-carbonyl group of the ARG393 residue, these two molecules form a stable 1:1 complex. In recent decades, several antithrombins have been identified. These molecules inhibit several coagulation factors. For example, some of these include the following: thrombin, Factor Xa, Factor IXa, Factor XIIa, Factor XIa and kallikrein. Substance H Over time, insects that feed on human blood have evolved various physiologic mechanisms that enhance their survival. One such mechanism involves a highly sulfated glycosaminoglycan that displays both antithrombotic and anticoagulant properties. This compound is known as Substance H. Glycosaminoglycans generally consist of similar saccharide units and functional groups which occur repetitively. The functional groups are typically derived from larger cell-surface mucopolysaccharides and contain a high density of negative charges. This inherently anionic composition gives glycosaminoglycans the ability to function as cation exchangers and complexing agents. Various biochemical analyses have demonstrated that Substance H is derived from a larger precursor molecule, prosubstance H.
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Approximate Word count = 3025
Approximate Pages = 12 (250 words per page)