Enzymes are defined as biological catalysts that support all chemical reactions in living organisms (plants and animals). The regulation of enzymes has been a key element in clinical diagnosis because of their role in maintaining life processes. The macromolecular component of all enzymes consists of protein, except in the class of RNA catalysts called as ribozymes. The word ribozyme is derived from the ribonucleic acid enzyme. Many ribozymes are molecules of ribonucleic acid which catalyze reactions in one of their own bonds or among other RNAs.
Enzymes exist in all fluids and tissues of the body. Intracellular enzymes catalyze all the reactions that occur in metabolic pathways. The enzymes in plasma membrane regulate catalysis in the cells in response to cellular signals and enzymes in the circulatory system regulate clotting of blood. Almost all the significant life processes are based on the enzyme functions.
Types of Enzymes
Earlier, enzymes were assigned names based on the one who discovered it. As knowledge reached, classification became more comprehensive. According to the International Union of Biochemists (I U B), enzymes are divided into six functional classes:
|SL no||Classification||Biochemical property|
|1||Oxidoreductases||Acts on any chemical group to remove or add hydrogen atoms|
|2||Hydrolases||Adds water to a bond and hydrolyze it.|
|3||Transferases||Transfers functional groups among acceptors and donors molecules.|
|4||Lyases||Adds water, carbon dioxide or ammonia across double bonds or eliminate these to create double bonds.|
|5||Ligases||Catalyze reactions wherein two chemical groups are linked with the help of energy from ATP.|
|6||Isomerases||Carry out different types of isomerization like mutase reactions and L to D isomerizations.|
These rules assign each enzyme a unique value or number. The IUB system specifies a name for every enzyme. Each name consists of a substrate, the product, and the enzyme’s functional class.
Mechanism of Enzyme Action
The basic mechanism of enzyme action to catalyze chemical reactions begin at the binding of the substrate with the active site of the enzyme. This active site is the specific area that combines with the substrate.
The favorable model of enzyme-substrate interaction is called induced-fit model. This model states that the interaction between substrate and enzyme is weak and these weak interactions induce conformational changes rapidly and strengthen binding and bring catalytic sites close enough to substrate bonds. There are four major possible mechanisms of catalysis.
- Catalysis by Bond Strain:
The induced structural rearrangements in this type of catalysis produce strained substrate bonds that attain transition state more easily. The new conformation forces substrate atoms and catalytic groups like aspartate into conformations that strain substrate bonds.
- Covalent Catalysis:
The substrate is oriented to active place on the enzymes in such a manner that a covalent intermediate develops between the enzyme and the substrate, in catalysis that occurs by covalent mechanisms. The best example of this is involving proteolysis by serine proteases that have both digestive enzymes and various enzymes of blood clotting cascade. These proteases have an active site serine whose R group hydroxyl produces a covalent bond with a carbonyl carbon of a peptide bond and causes hydrolysis of the peptide bond.
- Catalysis Involving Acids and Bases:
Other mechanisms also contribute to the completion of catalytic events that are initiated by strain mechanism like the use of glutamate as a general acid catalyst.
- Catalysis by Orientation and Proximity:
Enzyme-substrate interactions bring reactive groups into proximity with one another. Also, groups like aspartate are chemically reactive and their proximity and towards the substrate favors their involvement in catalysis.
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