Mechanism of Enzyme Catalysis

An enzyme attracts substrates to its active site, catalyses chemical reactions that produce products, and then allows the products to dissociate. Enzyme-substrate complexes are formed when enzymes are combined with their substrates. A general mechanism of action of an enzyme is to reduce the activation energy. The activation energy of an enzyme is increased with decreasing pH value. In this article, we shall explore the mechanism of enzyme catalysis importance and answer some mechanism of enzyme catalysis jee questions. 

Enzyme catalysis:

• In catalysis, a substance known as a catalyst is used to change the rate of a reaction (the catalyst does not take part in the reaction; its composition and concentration remain unchanged).
• In chemistry, a catalyst is a substance that increases reaction rates.
• Plants and animals rely on enzymes to facilitate and speed up many vital biochemical reactions. 
• Enzyme catalysis is the application of enzymes as catalysts.
• A nitrogen-containing enzyme is a complex compound. 
• These compounds are naturally produced in the bodies of animals and plants. 
• When dissolved in water, enzymes form a heterogeneous mixture of high molecular mass proteins. 
• They are responsible for a wide range of reactions that take place in the body of living beings.

Characteristics of enzyme catalysis:

• An enzyme catalyst can transform up to a million molecules of the reactant in a second. As a result, enzyme catalysts are considered highly efficient.
• Biochemical catalysts are unique to certain reactions, which means they cannot be used for multiple reactions.
• An optimum temperature is the temperature at which a catalyst is most effective. Regardless of the temperature, the activity of the biochemical catalysts declines.
• The pH of a solution is crucial for biochemical catalysis. The catalyst should be in an apH range between 5-7.
• In the presence of coenzymes or activators, such as Na+ or Co2+, enzyme activity increases. This is due to the weak bond between the metal ion and the enzyme.

Mechanism of enzyme catalyst:

Enzymes have a number of cavities on their surface. There are groups like -COOH, -SH, etc. in these cavities. Biochemical particles have active centres like this. As a key fits into a lock, so does the substrate, which has the opposite charge to the enzyme. The active groups in the complex forms lead to the decomposition of the products. As a result, two steps are involved:

The first step is to combine enzymes and reactants :-

E+R→ER

The disintegration of the complex molecule to produce the product is step two :-

ER→ E+R

Number of mechanisms:

1. Proximity. Enzymes can bring molecules together in a solution. For example, in a free solution, transferring a phosphate group from ATP to glucose has an extremely low probability of the two molecules coming near together. There are numerous molecules with which the ATP and sugar could collide. Allowing ATP and sugar to bind independently and tightly to an enzyme’s active site improves their ability to react with each other.
2. Orientation: Even when two molecules collide with enough energy to trigger a reaction, the result isn’t always the same. They must be orientated so that the collision energy is passed to the reactive link. Enzymes bind substrates to drive reactive groups in the direction of a reaction.
3. Induced fit: Enzymes can be employed in a number of different ways. In this way, they differ from solid catalysts like metal catalysts used in chemical hydrogenation. After binding its substrates, an enzyme’s conformation changes, driving the substrates into a stretched or deformed structure that mimics the transition state. Hexokinase closes like a clamshell when it binds to glucose. In this structure, the substrates are forced into a reactive state.
4. Reactive amino acid groups: The side chains of amino acids contain a number of reactive residues. For example, histidine can absorb and/or supply a proton from or to a substrate. Before a serine side chain mixes with water in hydrolysis processes, an acyl group can be linked to it. When enzymes with specific catalytic activity are present near a substrate, the reactions that use it speed up. For example, a proton-coupled to histidine can be transported to a basic group on a substrate right away.
5. Coenzymes and metal ions: In addition to their amino acid side chains, enzymes can provide a variety of reactive groups. Coenzymes are biomolecules that provide chemical groups to facilitate catalysis. During catalysis, coenzymes, like enzymes, do not change. This separates them from other substrates, such as ATP, transformed by enzyme action. Unlike other enzymes, coenzymes are not made up of protein. In the active sites of many enzymes, metal ions can be found bound to the enzyme and sometimes to the substrate.

• Proteins lack chemical functional groups, which coenzymes give.
• Only sulfhydryl groups on amino acids, for example, may engage in oxidation and reduction reactions, and disulfide formation/breakage does not give enough reducing power to change the functional groups of most biomolecules.
• As electron acceptors and donors, one of several coenzymes, usually Nicotinamide Adenine Dinucleotide (NAD) or Flavin Adenine Dinucleotide (FAD), is required.

Ways that enzyme catalyses reactions

• Enzymes use a number of ways to catalyse processes. Here are a few examples:
• Enzymes have the ability to destabilise bonds within the substrate.
• Proximity and orientation: When an enzyme binds to a substrate, conformational changes in the enzyme might bring reactive groups closer together or orient them so they can react.
• Bond polarisation and reaction speed can be affected by the presence of acidic or basic groups in proton donors and acceptors.
• Electrostatic catalysis: The active complex can be stabilised by electrostatic attraction between the enzyme and the substrate.
• Covalent catalysis reduces the energy of the transition state by forming covalent bonds with side chains or cofactors.
• As a result, enzymes demonstrate that evolution has generated highly powerful catalysts.

Conclusion

An enzyme attracts substrates to its active site, catalyses the chemical process that produces products, and then dissociates the products (separate from the enzyme surface). The enzyme-substrate complex is the combination of an enzyme and its substrates.