The physical aspects of enzyme functioning

The discussion of the thermodynamics and kinetics of protein reactions leads to the conclusion, that for the proteins postulates determining the applicability of Vant'-Hoff and Arrhenins equations are as a rule not fulfilled. It can be explained by the fact that proteins are kinetically unequilibrated structures with rigid memory on various organization levels, and the degree of kinetic unequilibrium changes with temperature, pH, ionic strength, etc. A new qualitative concept of the physical mechanism of elementary acts in enzyme catalysis is suggested. This concept is based on the postulate, according to which the conformational changes of the substrate-enzyme complex accompanying the substrate binding by the enzyme active centre, are of the nature of relaxation and include not only the breaking of old and formation of new secondary bonds in protein macromolecule, but also chemical changes necessary to transform the substrate molecule into a molecule or molecules of product. This conformational relaxation is essentially the elementary act of enzymatic reaction, and the rate of substrate-product transformation is determined by the rate of this conformational change. The rate of the relaxation, i.e. the rate of the enzyme reaction, changes with temperature due to changes in the macromolecule initial conformation and consequently in the path of its subsequent relaxation, rather than to those in the number of molecules with energies sufficient to overcome the activation barrier.