Transglutaminases, polymer

Dudek SM, Johnson GV. Transglutaminase facilitates the formation of polymers of the beta-amyloid peptide. Brain Res 1994 651 129-133. 

The most important reaction in blood clotting is the conversion, catalyzed by thrombin, of the soluble plasma protein fibrinogen (factor 1) into polymeric fibrin, which is deposited as a fibrous network in the primary thrombus. Thrombin (factor 11a) is a serine proteinase (see p. 176) that cleaves small peptides from fibrinogen. This exposes binding sites that spontaneously allow the fibrin molecules to aggregate into polymers. Subsequent covalent cross-linking of fibrin by a transglutaminase (factor Xlll) further stabilizes the thrombus. 

Selkoe, D. J., Abraham, C., and Ihara, Y. (1982). Brain transglutaminase In vitro crosslinking of human neurofilament proteins into insoluble polymers. Proc. Natl. Acad. Sci. USA 79, 6070-6074. 

Noncovalently associated fibrin is physiologically unsatisfactory because the dissociation of the fibrin results in recurrent bleeding. Fibrin monomer dissociation is prevented by formation of covalent cross-links between different Fnllm molecules. The result of this covalent cross-linking is an insoluble fibrin and a stable hemostatic plug. These cross-links are formed by the action of factor Xllla, plasma, and/or platelet transglutaminase (see below). Multiple cross-links are formed among a chains of several different fibrin monomers. This creates a molecular species designated a polymer (see Fibrinolysis below). Two... 

The solubility of TG treated films was compared to that of non treated films (Fig 3). Films obtained with deamidated gluten were soluble at 78% in water, the addition of putrescine didn t modify the film solubility (Fig 3). The action of transglutaminase induced a decrease in the film water solubility. The highest insolubility was obtained for a ratio putrescine / glutamine of 0.18 mole/mole and could be related to the formation of polymers of high molecular weight. 

FIG. 8 Variation of In (Vq/N,) as a function of crosslinking time for emulsions stabilized by 0.05% P-casein polymers crossUnked by transglutaminase. N, is the concentration of droplets at time t. No is the initial concentration of droplets at time 0. The ratio of NqIN, was calculated from the turhidity measurement. The smaller the ratio change, the more stable the emulsion is. A typical crosslinking reaction system contained 1% P-casein in 0.1 M tris-HCl buffer, pH 7.5, at the ratio of enzyme to substrate of 4.25 units/g protein. The reaction mixtures were incubated at 37°C for the period shown in the figure, and the reaction was terminated at various time intervals by heating up to 85°C for 5 min. (From Ref. 41.)... 

Another interesting biomimetic application of transglutaminase is the possibility to obtain in situ gelling hydrogels. In these approaches, polymer crosslinking and gel formation are modeled on crosslinking operations found in biology. 

The formation of cross-hnks relies on the abiUty of an enzyme to induce the formation of a covalent bond. Since most enzymes are very specific to their substrate the polymers have to be modified with specific functionalities to allow enzymatic cross-finking to take place. Transglutaminase is able to form... 

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