Plasmin inhibitors

Although the precise mechanism of plasminogen activation is unknown, three principal theories have developed based on studies of the in vitro activation of native human plasminogen. Activation of native Glu-plasminogen in the absence of any plasmin inhibitor yields Lys —plasmin plus the so-called pre-activation peptides (PAP) formed by cleavage at LySg2 S E3 Activation takes place by a two-step mechanism in... 

The high affinity LBS is involved in the interaction of plasminogen with fibrin, a2-antiplasmin, and a plasmin inhibitor called histidine-rich glycoprotein. It has been observed that plasminogen activation takes place on the surface of fibrin and that a2-antiplasmin competitively inhibits the plasminogen—fibrin interaction at the high affinity LBS. 

One of the most efficient plasmin inhibitor is a2-PI (70 kDa), which is synthesized by the liver, secreted into the blood circulation, where its concentration is 1 pM. It rapidly forms equimolar complex with plasmin, and in this complex, the active site of the enzyme is irreversibly blocked. The complex, thereafter, is removed by the liver. It is remarkable that when plasmin is bound to its substrate (fibrin), it is protected against its primarily inhibitor, a2-PI the rate of inactivation decreases by 400-fold (Fig. 4) [3]. 

There are several additional plasmin inhibitors in the blood, e.g., a2-macroglobulin, ai-proteinase inhibitor, antithrombin, but their role in the control of fibrinolysis is questionable, because their action on plasmin is eliminated by fibrin. 

Fibrinolytics. Figure 2 Various fibrin structures for plasmin. Fibrinogen (Fg) is converted to fibrin (F) by thrombin (T), and thrombin can also convert factor XIII (XIII) to activated factor XIII (Xllla). The latter produces crosslinks between fibrins (FxxF) and also may crosslink fibrin with a2-plasmin inhibitor (FxxFxxPI). The efficiency of digestion of these plasmin substrates by plasmin, resulting in the soluble fibrin degradation products (FDP), is different. The amount of FDP formed in time is expressed in arbitrary units. 

Fibrinolytics. Figure 4 Inactivation of plasmin by a2-plasmin inhibitor Effect of fibrin. The inactivation rate of free plasmin is very rapid (the second order rate constant k 430 104M-1s-1), while of fibrin bound plasmin is slow (the second order rate constant k 1 104M"1s"1). Inactivation of plasmin in the figure is shown in arbitrary units. Abbreviations plasmin (P), fibrin (F). 

The a2-plasmin inhibitor, a single-chain glycoprotein (70 kDa), forms rapidly an equimolar complex with plasmin, where the enzyme loses its activity. It is synthesized by the liver and secreted into the blood circulation, where its concentration is 1 pM. 

A plasmin inhibitor such as aprotinin used for blood collection, while effective in inhibiting activation of plasminogen by urokinase, is ineffective against the ac-... 

Cyanobacteria -Microcystis aeruginosa Micropeptins 478-A and -B -peptide-based plasmin inhibitors Cyanopeptolins A-D -protease inhibitors Cyanopeptolin 963A-chymotrypsin inhibitor 120 6, 262 263... 

Inactivation of the fibrinolytic system can be achieved by plasmin inhibitors, such as -aminocaproic acid, p-aminomethylbenzoic acid (PAMBA), tranexamic acid, and aprotinin, which also inhibits other proteases. 

The prevalent Microcystis aeruginosa has afforded the plasmin inhibitors micropeptins 478-A (1115) and 478-B (1116) (1133). The terrestrial cyanobacterium Scytonema hofmanni PCC 7110 gives rise to scyptolins A (1117) and B (1118), which contain the 3-chloro-A-methyltyrosine residue (1134). The binding of 1117 to pancreatic elastase has been determined by X-ray crystallography (1135). Myriastramide B (1119) was isolated from the Philippine sponge Myriastra clavosa and features a novel chlorinated ether moiety (1136). 

Ishida K, Matsuda H, Murakami M, Yamaguchi K (1997) Micropeptins 478-A and -B, Plasmin Inhibitors from the Cyanobacterium Microcystis aeruginosa. J Nat Prod 60 184... 

Farkye, N. Y. and Fox, P. F. (1991). Preliminary study on the contribution of plasmin to proteolysis in Cheddar cheese Cheese containing plasmin inhibitor, 6-aminohexanoic acid.. Agric. Food Chem. 39, 786-788. 

Sakata, Y., and Aoki, N. (1980). Cross-linking of a2-plasmin inhibitor to fibrin by fibrin-stabilizing factor./. Clin. Invest. 65, 290-297. 

A fibrin clot containing adsorbed plasmin inhibitors is difficult to define in a chemical or physical sense. Generally, when enzyme reactions occur at surfaces, the porosities and adsorption properties erf which are variable, the reproducibility of enzyme assay methods is questionable. The proteinoses, to which belong the most important pharmaceutical enzymes, may present some difficulties when natural substrates (protein ) are prescribed. Here, the application of a parallel run with a reference standard is recommended. 

Acide aminocaproique Epsilcapramin) Use antifibrinolytic, plasmin inhibitor... 

Plasmin inhibitors. s-Aminocaproic acid as well as tranexamic acid and p-aminomethyl-benzoic acid (PAMBA) are plasmin inhibitors that can be useful in bleeding complications. They exert an inhibitory effect by occupying the fibrin binding site of plasminogen or plasmin. 

Schwartz BS, Williams EC, Coulau MG, Mosher DF. Epsilon-aminocaproic acid in the treatment of patients with acute promyelocytic leukemia and acquired alpha-2-plasmin inhibitor deficiency. Ann Intern Med 1986 105(6) 873-7. 

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