Enzymes are macromolecular biological catalysts that accelerate chemical reactions. The molecules upon which enzymes may act are called substrates, and the enzyme converts the substrates into different molecules known as products. Almost all metabolic processes in the cell need enzyme catalysis in order to occur at rates fast enough to sustain life.
The study of enzymes is called enzymology and a new field of pseudoenzyme analysis has recently grown up, recognising that during evolution, some enzymes have lost the ability to carry out biological catalysis, which is often reflected in their amino acid sequences and unusual ‘pseudo catalytic’ properties.
Classifications of Enzymes
According to the International Union of Biochemists (I U B) enzymes are divided into six functional classes and are classified based on the type of reaction in which they are used to catalyze. The 6 types of enzymes are oxidoreductases, hydrolases, transferases, lyases, isomerases, ligases.
- Oxidoreductases: These catalyze oxidation and reduction reactions,e.g. pyruvate dehydrogenase, which catalyzes the oxidation of pyruvate to acetyl coenzyme A.
- Transferases: These catalyze the transfer of a chemical group from one compound to another. An example is a transaminase, which transfers an amino group from one molecule to another.
- Hydrolases: They catalyze the hydrolysis of a bond. For example, the enzyme pepsin hydrolyzes peptide bonds in proteins.
- Lyases: These catalyze breakage of bonds without catalysis, e.g. aldolase (an enzyme in glycolysis) catalyzes the splitting of fructose-1, 6-bisphosphate to glyceraldehyde-3-phosphate and dihydroxyacetone phosphate.
- Isomerases: They catalyze the formation of an isomer of a compound, example, phosphoglucomutase catalyzes the conversion of glucose-1-phosphate to glucose-6-phosphate (transfer of a phosphate group from one position to another in the same compound) in glycogenolysis (conversion of glycogen to glucose for quick release of energy.
- Ligases: Ligases catalyze the joining of two molecules. For example, DNA ligase catalyzes the joining of two fragments of DNA by forming a phosphodiester bond.
Examples of Enzymes
- Beverages: Alcoholic beverages generated by fermentation vary a lot based on many factors. Based on the type of the plant’s product which is to be used and the type of the enzyme applied, the fermented product varies. For Ex: Grapes, honey, hops, wheat, cassava roots, and potatoes depending upon the materials available. Beers, wines and other drinks are produced from plant fermentation.
- Food Products: Bread can be considered as the finest example of fermentation in our everyday life. A small proportion of yeast and sugar is mixed with the batter for making bread. Then one can observe that the bread gets puffed up as a result of fermentation of the sugar by the enzyme action in yeast, which leads to the formation of carbon dioxide gas. This process gives the texture to the bread which would be missing in the absence of the fermentation process.
- Drug Action: Enzyme action can be inhibited or promoted by the use of drugs which tend to work around the active sites of enzymes.
Characteristics of Enzymes
- Enzymes are highly specific for a particular substrate. The active site of an enzyme has a strong affinity for a specific substrate, and will slightly change its conformation, known as an “induced fit” to accommodate the target substrate. This induced fit allows for a stabilized transition state, which lowers the activation energy of the reaction.
- Enzymes remain unchanged during the reaction itself. While the enzyme’s amino acid residues may break or form covalent bonds with the substrate, it will typically reform those bonds, enabling the enzyme to react with more substrates.
- Enzymes are very efficient, catalyzing about 1-10,000 molecules of substrate per second. Therefore, only a small number of enzymes are typically created under normal cellular conditions.
- Enzymes do not affect the equilibrium constant, or Keq. While the rate of conversion from substrate to product is increased, the vice versa is true.
- Enzymes can be allosterically controlled by a variety of means. There are cofactors and coenzymes that are necessary for enzymatic catalysis. Furthermore, there are also molecules that can allosterically inhibit protein function by modifying the conformational shape of the enzyme.