Trypsin activation energy

A new, more general, way to combine ab initio quantum mechanical calculations with classical mechanical free-energy perturbation approach (QM/FE approach) to calculate the energetics of enzyme-catalysed reactions and the same reaction in solution has been reported." The calculated free energies were in fairly good agreement with the experimental data for the activation energies of the first test case, amide hydrolysis in trypsin and in aqueous solution. 

TABLE 1. Calculated and experimental changes in the activation energy of the reactions catalysed by mutant trypsin and subtilisin, as compared to the wild type enzymes (kJ/mol). 

Unless the catalytic surface of the enzyme is altered, an environmental change should theoretically have no effect on the activation energy Lipase, trypsin, and pepsin follow the Arrhenius equation, but below 0°... 

Figure 7.2 Arrhenius plots for the trypsin catalysed hydrolysis of benzoyl L-arginine ethylester at pH 6.0 and 7.5. The difference in the activation energies of the two reactions is 30 kJ mole. This corresponds to the extra energy required to dissociate a proton from an imidazole group (pAT= 6.23) which has to be deprotonated in the active form of the enzyme.

Table 3 Calculated and Experimental Changes in the Activation Energy (kJ mor ) of the Reactions Catalyzed by Mutant Trypsin and Mutant Substilisin, as Compared to the Wild-type Enzymes ...

Warshel and collaborators (Warshel and Sussman, 1986 Warshel et al., 1988) developed the empirical valence bond method for obtaining free-energy differences and activation free energies. The effects of Gly-to-Ala mutations in trypsin were accurately simulated. This method was earlier applied to calculation of the potential surface for general acid catalysis of a disaccharide in solution and bound to lysozyme (Warshel and Weiss, 1980). 

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