[Conditions, necessary for realizing the catalytic effect of enzymes: role of the environment].
A hypothesis of enzymic catalysis was put forward according to which the energy of the exothermic reaction that takes place in aqueous medium is used for a shift of equilibrium in the endothermic reaction, a reaction involving hydrated ions. This occurs in accordance with the Le Chatelier's principle, and, as a result of water dissociation in a homogeneous medium, a gradient of H+ and OH- ions is generated at the water/protein interface. It follows from the hypothesis that the chemical conversion of the substrate to the product is preceded by the attack of hydrated ions on the protein and their association on the protein (attack of the nucleophilic agent followed by the acception of the proton). This results in the formation of a cyclic peroxide in the amino acid residue and a C=O-->[C=O]* transition. The return of the carbonyl to the ground state makes it possible to store a part of free energy and use it for converting the enzyme to a state with a higher conformational energy. Thus, we consider the electron excited state in the protein as a state necessary for dark reactions. This implies that, in addition to the effect of sorption of substrate on protein, another aspect of behavior of the dynamic system should be taken into account. All factors producing a real effect on the internal protein dynamics are important for the conformational transition and enzymic reaction as a whole, and the rate constant should be determined with allowance for these factors.
Dmitriev
L F
LF
Biological Department, Lomonosov Moscow State University, Vorob'evy Gory, Moscow, 119899 Russia. Dmitriev@mars.biophys.msu.ru
D002384:Catalysis; D004798:Enzymes / Q000378:metabolism*; D007700:Kinetics; D012996:Solutions
D004798:Enzymes; D012996:Solutions