Specificity of Enzymes in Biological Reactions

Enzymes are responsible for all the biological chemical reaction processes involved in living creatures. Most of the chemical reaction would not even occur if enzymes did not play a vital role in the process. Controlling the pace of chemical reactions while remaining unaffected is done by enzymes. Enzymes are substances that work as a catalyst (increasing rate of reaction with no changes in themselves) in living organisms. 

Enzymes increase the rate of reaction in all the components of a cell. This comprises food digestion, which breaks down large nutrition molecules (such as proteins, carbs, and lipids) into smaller ones; chemical energy conservation and transformation; and the creation of cellular macromolecules from smaller precursors. 

Hereditary disorders in humans, like phenylketonuria and albinism, are caused due to a lack of enzymes.

What are Enzymes Composed of? 

A big protein enzyme molecule is made up of one or more polypeptide chains of amino acids. The amino acid sequence determines the distinctive folding patterns of the protein's structure, which is required for enzyme specificity. 

If there is a temperature or pH change or fluctuations in enzymes there is a possibility of protein structure to lose its integrity as well as the capacity of enzymes. 

Cofactors are chemical components bound to several enzymes and are essential for enzyme activity as they are directly involved in catalysis. A cofactor might be a coenzyme (an organic molecule like a vitamin) or an inorganic metal ion. Some enzymes necessitate both. 

All enzymes were formerly considered to be proteins, but the catalytic activity of some nucleic acids known as ribozymes (or catalytic RNAs) has been established since the 1980s, challenging this premise.

What are the Examples of Enzymes? 

Almost all c plex biochemical reactions that occur in animals, plants, and microorganisms are regulated by enzymes, and there are many examples of this. Among the best-known enzymes are the digestive enzymes of animals. For example, the enzyme pepsin is an essential component of gastric juice, which helps the stomach break down food particles. Similarly, the enzyme amylase,  present in saliva, helps initiate digestion by converting starch into sugar.

In medicine, the thrombin enzyme is used to accelerate wound healing. There are enzymes also used to diagnose certain types of diseases. The cell wall enzyme lysozyme is used to kill bacteria.

Water and oxygen are used to break down hydrogen peroxide by the use of enzymes. Catalase protects organelles and tissues from damage by peroxides that are constantly produced as a result of metabolic reactions.

What Factors Affect the Enzyme Activity? 

The activity of an enzyme is affected by a number of factors, including the concentration of the substrate and the presence of inhibitory molecules.  When all the active centers of enzyme molecules are involved the rate at which the enzymatic reaction happens also increases by increasing the concentration of substrate and will eventually reach its maximum rate thereafter. Thus, the rate of an enzymatic reaction is determined by the rate at which the active center converts a substrate into a product.  Inhibition of enzymatic activity occurs in a variety of ways. 

Competition inhibition occurs when a molecule, such as a substrate molecule, binds to the active site and prevents the actual substrate from binding. Noncompetitive inhibition occurs when an inhibitor binds to an enzyme at a site other than the active site.  Another factor influencing enzyme activity is allosteric regulation, which can include both stimulation and inhibition of enzyme action. The inhibition and allosteric stimulation cause cells to produce the substances as well as energy when it is needed to inhibit this production and the substance and energy are supplied accordingly.

Explain Enzyme Substrate Specificity?

Specificity is defined as the ability of an enzyme to choose an exact substrate from a group of the same chemical molecules. Actually, specificity is a molecular recognition mechanism that works through complementarity in conformation and structure between the enzyme and the substrate.

Types of Enzyme Specificity

Since the substrate should fit into the active site of the enzyme before catalysis can take place, only properly designed molecules may serve as substrates for a specific enzyme; in several cases, an enzyme will react with only one naturally taking place molecule. Two oxidoreductase enzymes will serve to describe the principle of enzyme specificity.

One (alcohol dehydrogenase) acts on the alcohol, the other (or the lactic dehydrogenase) on lactic acid; the two activities, even though both are oxidoreductase enzymes, they are not interchangeable - it means, alcohol dehydrogenase will not catalyze a reaction involved in the lactic acid or vice versa, because the structure of every substrate varies sufficiently to prevent its fitting into the active site of an alternative enzyme. Enzyme specificity is important because it distinguishes between the various metabolic pathways involving hundreds of enzymes.

Example

Not all enzymes are highly specific. For example, digestive enzymes such as chymotrypsin and pepsin are able to act on almost any protein the specificity of enzyme action, as they should if they are to act upon the differential types of proteins consumed as food. Furthermore, since thrombin only interacts with the protein fibrinogen, it is a part of a very delicate blood-clotting process that can only react with one compound in order to keep the system working properly.

When the enzymes were first studied, it was thought that most were "absolutely specific"—that they would react with only a single compound. However, in most cases, a molecule other than the natural substrate may be synthesized in the laboratory; it is enough such as the natural substrate to react with enzymes. These synthetic substrates' use has been valuable in understanding the enzymatic action. However, it should be remembered that, in the living cell, several enzymes are absolutely specific for the compounds found.

As a result, all enzymes isolated from a long distance are unique for the chemical reaction form they catalyze - oxidoreductases do not catalyze hydrolysis reactions, and hydrolases do not catalyze reactions involving both reduction and oxidation. Therefore, an enzyme catalyzes a particular chemical reaction but can be able to do so on many similar compounds.

Mechanism of Enzymatic Action

An enzyme attracts substrates to its active site, then catalyzes the chemical reaction that creates the products before dissociating the products (separate from the surface of the enzyme). The combination formed by an enzyme and its substrates is known as the enzyme-substrate complex. A ternary complex is made up of one enzyme and two substrates, whereas a binary complex is made up of one enzyme and one substrate. These substrates are attracted to the active site by hydrophobic and electrostatic forces that are known as noncovalent bonds because they are physical attractions but not chemical bonds.

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Assume two substrates (\[S_{1} and S_{2}\]) bind to the enzyme's active site in step 1 and then react in step 2 to generate products (\[P_{1} and P_{2}\]). In step 3, the products dissociate from the enzyme surface by releasing the enzyme. The enzyme, which is unchanged by the reaction, is capable of reacting with additional substrate molecules in this way several times per second to form the products. The phase in which the actual chemical transformation occurs is of great interest, and while much is known about it, it is still not fully understood. Generally, there are two types of enzymatic mechanisms, one is the so-called covalent intermediate forms, and the other is none forms.

In the mechanism, where a covalent intermediate—it means an intermediate is having a chemical bond between the enzyme and substrate—forms, for example, one substrate, B―X, reacts with the group N on the enzyme surface to produce an enzyme - B in the intermediate compound. The intermediate compound then reacts with the second substrate, Y, to create the BY and X products.

Several enzymes catalyze reactions by this mechanism type. Acetylcholinesterase can be used as a particular example in the sequence given here. The two substrates (S1 and S2) for the acetylcholinesterase are acetylcholine (it means B―X) and water (Y). After the acetylcholine (B―X) binds to an enzyme surface, a chemical bond is produced between the acetyl moiety (B) of acetylcholine and group N (which is part of amino acid serine) on the surface of the enzyme.

The formation result of this bond, known as an acyl–serine bond, is one product, choline (X), and enzyme-B intermediate compound (which is acetyl–enzyme complex). Then, the water molecule (Y) reacts with the acyl–serine bond to produce the second product, acetic acid (B―Y), that dissociates from the enzyme. Acetylcholinesterase is regenerated and can react with the other acetylcholine molecule once more. A double displacement reaction is a type of reaction that involves the formation of an intermediate compound on an enzyme surface.

Conclusion

Before we learn and understand the substrate specificity of enzymes and explain the mechanism, one should know the most basic concepts and understand in detail about the enzymes. Here, Vedantu provides an easy understanding of this chapter as they are designed by the most experienced teachers. Also, the students can come across sample papers, revision notes, comprehensive question banks, and many other resources that can help in scoring good marks in the exam.