Chymotrypsin catalytic factors

I Cyclodextrins are excellent enzyme models Catalysis and induced fit. Due to their cavities, which are able to accommodate guest (substrate) molecules, and due to the many hydroxyl groups lining this cavity, cyclodextrins can act catalytically in a variety of chemical reactions and they therefore serve as good model enzymes. Thus, benzoic acid esters are hydrolyzed in I aqueous solution by factors up to 100 times faster if cyclodextrins are added. The reaction in- j volves an acylated cyclodextrin as intermediate which is hydrolyzed in a second step of the j reaction, a mechanism reminiscent of the enzyme chymotrypsin. The catalytic efficiency can. be further enhanced if the cyclodextrins are suitably modified chemically so that a whole range of artificial enzymes have been synthesized [551-555, 556, 563, 564]. 

Several vital processes rely on clan PA peptidases. Chief among them are blood coagulation and the immune response, which involve cascades of sequential zymogen activation. In both systems, the chymotrypsin-fold peptidase domain is combined with one more associated protein domains, including apple, CUB, EGF, fibronectin, kringle, sushi, and von Willebrand factor domains. These protein domains are on the N-terminus as an extension of the propeptide segment of the peptidase. Such a trend of N-terminal-associated domains in the SIA peptidase family is common across all forms of life. The domain architecture pairs well with the zymogen activation mechanism, which liberates the proper N-terminus to enable catalytic activity. Often, the associated protein domains remain attached to... 

Thrombin, EC 3.4.21.5, factor Ila, fibrino-genase, a serine protease capable of producing a thrombus or blood clot. Thrombin activates platelets and regulates the behavior of other cells via G protein-coupled protease-activated receptors. It consists of two chains (Mr 36.5 kDa). The A chain (human 36 aa) of a a-thrombin, without known function, is linked by a single disulfide bond to the catalytic B chain (259 aa) which is homologous to the catalytic domains of trypsin and chymotrypsin. Six additional Cys residues within the B chain form three intrachain disulfide bridges. Furthermore, the B chain is glycosylated on Asn . Thrombin is derived from its... 

FIG. 11 Combination of two factors regulating enzyme catalytic activity variation in the surfactant concentration and addition of water-miscible organic solvents, (a) Peroxidase in the system AOT-water/glycerol-octane at water/glycerol volume ratios (O) 100 0 ( ) 20 80. (b) a-Chymotrypsin in the system AOT-water/glycerol-octane at water/glycerol volume ratios (O) 100 0 ( ) 6 94. Dashed lines show the catal5dic activities of the enzymes in aqueous solution. (From Ref. 44.)... 

A-a-decyL-L- phenylalanine-(2-aminopyridine)amide can be regarded as a surfactant with a headgroup imitating the transition state of the a-chymotrypsin catalyzed hydrolysis of peptides. Using this TSA as a template, catalytically active silica particles were obtained. To test the reactivity, the hydrolysis of an arginine derivative was investigated (Fig. 18b). Compared to the control material prepared without template, a rate enhancement of a factor of 5 was observed. Furthermore, the catalytic silicas were shown to be enantioselective. Remarkably, the preferential... 

The reaction conditions can be optimized by examining the effect of different factors snch as water content, temperature, pH, surfactant concentration, reaction time, or product yield. Proteases are classified according to their catalytic mechanisms. Four mechanistic classes have been recognized by the International Union of Biochemistry and Molecular Biology serine proteases (chymotrypsin, trypsin, elastase, subtilisin), cysteine proteases (papain, cathepsins, caspases), aspartic proteases (pepsins, cathepsins, lennins), and metallo proteases. 

Enzymes may use any of the above mentioned modes of catalysis in order to catalyze a particular chemical reaction. For example, the imidazole ring of a histidine residue of the enzyme a-chymotrypsin (Section 4.4) can function as a general-base catalyst, while in the enzyme alkaline phosphatase, the same residue can function as a nucleophilic catalyst. Indeed, enzymes are complex catalysts which employ more than one catalytic parameter during the course of their action. It is by this successful integration of a combination of individual catalytic processes that a rate enhancement as high as 10 " may be achieved. Furthermore, it is this combination of factors which results in a specific catalyst. 

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