Thrombin biological activities

A new aspect of the PC-pathway is the efficacy of recombinant-APC in reducing mortality in patients with septic shock. Whether this is related to the inhibition of thrombin generation or due to other biological activities of APC is currently under investigation. 

Hirudin exhibits its anticoagulant effect by tightly binding thrombin, thus inactivating it. In addition to its critical role in the production of a fibrin clot, thrombin displays several other (non-enzymatic) biological activities important in sustaining haemostasis. These include ... 

GEA-3175 is more stable than GEA-3162 in vitro but still retains its biological activity [95]. The release of NO and NO2 by GEA 3175 was increased 140-fold in the presence of human plasma, as analyzed by ozone chemiluminescence [94]. GEA 3175 inhibited agonist-induced platelet aggregation and induced a more than 4-fold increase in platelet cGMP without affecting cAMP levels [94]. Thrombin-stimulated rises in the cytosolic free Ca2+ concentration and secretion were dose-dependently inhibited by GEA 3175. GEA 3175 showed a reduced capacity to inhibit platelet aggregation of uremic platelets compared to controls [96]. 

In the case of platelet-derived factor XIII, the resultant product (a )2, is the activated form. Thrombin action on plasma-derived factor XIII generates an a 2jfi2 dimer, which is devoid of transglutaminase activity. However, in the presence of Ca +, the a P chains dissociate, yielding the biologically active a 2. 

After the early discovery of a tyrosine 0-sulfate residue in bovine fibrinopeptide B, 15 this posttranslational modification which occurs ubiquitously in proteins was also detected in a series of biologically active peptides such as the neurohormones of the gastrin/cholecysto-kinin (CCK) family of peptides, phyllokinin, Leu-enkephalin, and the thrombin inhibitor hirudin listed in Table 1. 

The oleosin fusion procedure was used for the purification of the commercially valuable plant-based blood anticoagulant hirudin in transgenic Brassica carinata and Brassica napus. Hirudin, a natural protein from the medicinal leech Hirudo medicinalis, is superior to other anticoagulants such as heparin. Recombinant hirudin was cleaved from oil-bodies using endoproteinase Factor Xa. Released hirudin was biologically active, as determined by a colorimetric thrombin inhibition assay. 

PRECURSOR. In biological systems, an intermediate compound or molecular complex present in a living organism which, when activated physiochemically, is converted to a specific functional substance. Sometimes the prefix pro is used to indicate that a compound in question plays the role of a precursor. Examples from the history of vitamin and other essential chemical developments include ergosterol (pro-vitamin D2), which is activated by ultraviolet radiation to form vitamin D carotene (provitamin A) is a precursor of vitamin A prothrombin forms thrombin upon activation in the blood-clotting mechanism. 

Very recently, (3-lactam antibiotics have been shown to offer neuroprotection by increasing glutamate transporters expression via gene activation [15] in addition, the discoveries of new biologically active (3-lactams such as cholesterol acyl transferase inhibitors [16-18], thrombin inhibitors [19], human cytomegalovirus protease inhibitors [20], matrix-metallo protease inhibitors [21], inhibitors of human leukocyte elastase (HLE) [22, 23] and cysteine protease [24, 25], and apoptosis inductors [26, 27] have provided much needed motivation for continuous development of new (3-lactam systems. 

Several representatives of the class of the (3-lactams can effectively inhibit proteases [366, 367]. For instance, the 2-azetidinone I of Fig. 38 has been identified [368] as a powerful and selective inhibitor of thrombin, a serine protease involved in both venous and arterial thrombotic episodes [369]. More recently, p-lactam II (Fig. 38) has been found to display inhibition of tryptase at the subnanomolar level and suppress induced inflammation in animal lungs [370]. These compounds featured an m-guanidyl-substituted n-propyl side chain at the C-3 position and a carboxylic residue at the C-4, both essential for biological activity. 

Figure 12. The numbers of overlapping potential 4-point pharmacophores for ligands with those calculated for the active sites of thrombin, factor Xa, and trypsin on the basis of complementary site-points the arrow points to the enzyme for which the ligand shows biological activity).

Design, Synthesis and Biological Activity of Novel Rigid Amidino-Phenylalanine Derivatives as Inhibitors of Thrombin. 

The synthesis of ketomethylene pseudopeptide analogues was accomplished by L. Cheng et al., and their biological activity as thrombin inhibitors was tested. These analogues were prepared through a modified Dakin-West reaction under mild conditions and in almost quantitative yield. The required anhydride was prepared from monomethyl succinate, and a large excess of it was mixed with the tripeptide substrate in pyridine in addition to triethylamine and catalytic amounts of DMAP. The reaction mixture was heated for one hour at 40-50 °C. 

Mack, H., Pfeiffer, T, Hornberger, W, Bohm, H. J., Hoffken, H. W. Design, synthesis and biological activity of novel rigid amidino-phenylalanine derivatives as inhibitors of thrombin. J. Enzyme Inhib. 1995, 9(1), 73-86. 

---