2.1. Enzymes as Catalysts. Active Site of the Enzyme
The transformations of various molecules in the cells of the body catalyze enzymes. Enzymes are proteins that have a specific primary, secondary, tertiary, and sometimes quaternary structure.
Enzymes are a group of proteins that have an ability to accelerate chemical reactions. Enzymes distinguish three unique properties from other catalysts:
► high efficiency of action;
► action specificity;
► ability to be regulated by other molecules;
By their function, enzymes are biological catalysts. The essence of the action of enzymes, as well as inorganic catalysts, is:
► in the activation of reactive molecules;
► in dividing the reaction into several stages, the energy barrier of each of which is lower than that of the overall reaction.
However, enzymes will not catalyze energy-impossible reactions; they only accelerate those reactions that can take place under these conditions. It is known that for the implementation of a chemical reaction, it is necessary that the reacting substances have total energy higher than the value called the energy barrier of the reaction. Enzymes are proteins that bind to a molecule, or substrate, to modify it and lower the energy required to make it react. The rate of reaction is given by the Arrhenius equation. In this figure, the plot of energy versus the progress of a reaction is shown (Fig. 2.1). Reactants have higher energy than products. The energy of the reactants increases and then decreases to the final product energy. The highest point in the curve represents the energy of the intermediate state in the reaction. The energy required to achieve the intermediate state is the activation energy of the reaction. Enzymes lower the activation energy of a given reaction, shown by the blue curve.