3.4 Enzyme Inhibition
The term enzyme inhibition means to stop the enzyme from its expression (functioning), usually by enzyme inhibitors or due to a change in temperature or pH. Such molecules or substances that stop enzyme activity are called enzyme inhibitors, such as drugs, toxins, products of enzymes, etc.
Some of the poisons are enzyme inhibitors, that's why a person exposed to poison may die. On the other hand, there are enzyme activators that bind to enzymes to increase enzyme activity.
Types of Inhibitors:
Generally, two main types of enzyme inhibitors are irreversible and reversible inhibitors.
Irreversible Inhibitors:
These inhibitors stop enzyme activity permanently either by destroying (denaturing) the active site of the enzyme or occupying the active site by making a covalent bond with the chemic active site. The irreversible inhibitors often contain reactive functional groups e.g., aldehydes, and alkenes. These electrophilic groups make covalent bonds with side chains.
The irreversible inhibitors may be snakes, drugs, etc. acid in created regulatory or artificial e.g., poisons, venom.
Reversible Inhibitors:
Such inhibitors attach to enzymes with non-covalent interactions such as hydrogen bonds, and are hydrophobic. interactions and ionic bonds. These inhibitors generally do not undergo chemical reactions when bonded to enzymes and are easily removed from enzymes. Reversible inhibitors are of two types.
Competitive Inhibitors:
Such inhibitors which have an Isimilar shape to the substrate molecule hence compete with the substrate to occupy the active site. The process of inhibition depends on the concentration of substrate and inhibitors. With the high concentration of inhibitors, the chances of inhibition are also high.
Non-Competitive Inhibitors:
These inhibitors do not possess structural similarities with the substrate molecule and, therefore, attach to the allosteric site of the enzyme rather than the active site. The attachment of inhibitors changes the shape of the active site. Thus substrate cannot bind with the active site. Such types of inhibitors are not affected by substrate concentration.
Feed Back Inhibitons:
The production of enzymes, hormones, and other products should be limited to maintain homeostatic conditions. The overproduction of any product in the body may prove fatal.
The mechanism through which the production of different the body is known as the feedback mechanism.
controlled in the biochemical Many enzyme-catalyzed reactions are carried out pathways. In these pathways, the product of the first reaction becomes the substrate for the next reaction. At the end of the pathway, a desired product is synthesized. To regulate the concentration of that product the biochemical pathway needs to be shut down.
This is done through a feedback mechanism (automatic system) e.g., the amino acid aspartate changes into threonine through a sequence of five enzymatic reactions. When threonine production becomes sufficient, it starts accumulating on the allosteric site of the enzyme. This changes the shape of the active site as a result threonine production stops.
3.5 Nomenclature of Enzymes (classification of enzymes)
The name of an enzyme is often formed by adding "ase" to the name of substrate. They are named for the action they perform e.g., hydrogenase is an enzyme that removes hydrogen atoms from its substrate and cellulase which breaks down cellulose.
Oxidoreductases:
These enzymes catalyze different types of oxidation-reduction reactions i.e. removing or adding electrons or hydrogen ions from or to the substrate. The sub-classes of these enzymes are oxidases, oxygenases, and peroxidases.
Transferases:
These enzymes cause the transfer of groups from one molecule to another molecule called transferases. Examples of such groups are the amino group, carboxyl group, methyl, and carbonyl group. Examples of transferase enzymes are hexokinases which transfer phosphate groups from ATP to glucose.
Hydrolases:
These enzymes break down proteins, fats, and carbohydrates by adding water so are called hydrolases e.g., lipase, sucrase, maltase, cellulase,
Lyases:
These enzymes catalyze the breakdown of the specific functional groups without hydrolysis e.g., decarboxylase, deaminases, add or remove amino groups, etc. bond, and remove or remove carboxyl group.
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