Biochemistry

3.4 GENERAL CONCEPTS ABOUT THE MECHANISM OF ACTION OF ENZYMES The mechanism of action of enzymes has not been studied enough. Current data allow to state only some general provisions on this issue. The action of enzymes as biological catalysts is based on their ability to accelerate reactions by reducing the activation energy of the substrate. The reaction can be started by overcoming the repulsive forces between the molecules that is due to external electrons. Enzymes deform the electron shells of substrates, thus facilitating the interaction between them. The energy necessary to bring the molecules into an active state is called the activation energy. It is used to overcome the energy barrier. This process can be carried out by the catalyst. For example, the activation energy required for the decomposition of hydrogen peroxide 2H 2 O 2 — > 2H 2 O + O 2 , without a catalyst, is 75.2 kJ/mol, with a catalyst - colloidal platinum - 50.2 kJ/mol, with the participation of the liver catalase enzyme - 8.3 kJ/mol. Thus, the role of a conventional catalyst (and to an even greater extent biological) is that it reduces the activation energy of the substrate. There are two theories of the mechanism of action of enzymes: the theory of intermediate compounds and adsorption. Theory of intermediates. The essence of the process is in the formation of an enzyme-substrate complex (Fig. 3.8). With direct interaction of the substrate with the active center of the enzyme, the latter in a certain way affects the substrate, causing the restructuring of its chemical bonds and thereby activating it. 5 P, P z Figure 3.8 - Scheme of the formation of the enzyme-substrate complex As an example, the proposed mechanism of action of fumarase (F), catalyzing the reaction of the formation of malic acid from fumaric acid: 89