Enzymes are a class of catalysts that increase the rate of many vital biochemical reactions in plants and animals. Enzymes are complex compounds containing nitrogen, and they are proteins that have high molecular mass and form a heterogeneous mixture when dissolved in water. Enzymes are responsible for various reactions that occur in the body of living beings and are highly efficient, with a single molecule of the enzyme catalyst transforming up to a million molecules of the reactant per second. Enzymes are unique to certain types of reactions, and the same catalyst cannot be used in more than one reaction. The effectiveness of a catalyst is maximum at its optimum temperature, and the activity of the biochemical catalysts declines at either side of the optimum temperature.
The mechanism of enzyme catalysis involves the binding of the substrate to the enzymes active site, which is a localized site where catalysis occurs. Enzyme-catalyzed reactions occur in at least two steps. In the first step, an enzyme molecule and the substrate molecule or molecules collide and react to form an intermediate compound called the enzyme-substrate complex. Once the enzyme-substrate complex forms, the enzyme is able to catalyze the formation of the product, which is then released from the enzyme surface. The structural changes that occur when an enzyme and a substrate join together bring specific parts of a substrate into alignment with specific parts of the enzymes active site. Amino acid side chains in or near the binding site can then act as acid or base catalysts, provide binding sites for the transfer of functional groups from one substrate to another, or aid in the rearrangement of a substrate.
Enzymatic catalysis involves several mechanisms, including covalent catalysis, acid-base catalysis, electrostatic catalysis, desolvation catalysis by approximation, coenzyme catalysis, and strain distortion. Enzymes have high substrate specificity and can even show regiospecificity that leads to the generation of stereospecific products. Enzymes only reduce energy barriers between products and reactants, so they always catalyze reactions in both directions and cannot drive a reaction forward or affect the equilibrium position, only the speed with which it is achieved.
