Introduction
The cell is the fundamental unit of life which serves as both its structural and functional foundation. Cells can use biocatalysts, referred to as enzymes, which have excellent catalytic efficiency, both substrate and reaction specificity. Enzymes are ideal for biological reactions due to their extraordinary catalytic power and high level of substrate specificity. They are essential for the metabolism of cells.
The complex protein molecules produced by living cells are known as enzymes or biocatalysts. Both the processes they catalyse and the reactants they choose, or substrates, are highly selective. An enzyme normally catalyses one chemical reaction or a group of related reactions.
Enzymes’ specificity concerning the reactions they catalyse is one of their characteristics that makes them so significant as diagnostic and research tools. A small number of enzymes exhibit the ability to catalyse only one specific reaction. Other enzymes will have a preference for a certain kind of functional group or chemical bond.
Table of Contents
Enzymes
An enzyme is a component that functions as a catalyst in living beings, controlling the frequency at which chemical reactions occur without changing the enzyme itself.
All biological activities in living organisms involve chemical reactions, and enzymes regulate most of them. Many of these activities would not occur at a significant rate without enzymes. Enzymes catalyse every aspect of cell metabolism.
Enzymes are useful in industrial and medical applications. Wine fermentation, bread leavening, cheese curdling, and beer brewing have all been done since the beginning of time, but not till the 19th century that it was realised that these events were the result of enzymes’ catalytic activity. Since then, enzymes have become more significant in industry applications involving organic chemical reactions. Enzymes are used in medicine for various purposes, including aiding wound healing, identifying diseases, and eliminating disease-causing microbes.
An enzyme has four primary features.
- They are very catalytic and can easily catalyse a chemical reaction.
- They enhance reactions while remaining consistent throughout.
- Enzyme effectiveness and function are easily affected by temperature, pH, and inhibitors.
- Enzymes seem to be quite specific and mainly catalyse only one type of substrate.
Mechanism of Enzyme Actions
An enzyme pulls substrates to its active site, catalyses the chemical reaction that produces the products, and then enables the dissociation of the products (detach from the enzyme surface). The enzyme and substrate complex is the interaction between an enzyme and its substrates.
One substrate and one enzyme constitute a binary complex, whereas two substrates and one enzyme constitute a ternary complex. The substrates are drawn towards the active site by hydrophobic and electrostatic forces, considered noncovalent bonds since they possess physical attractions and are not chemical bonds.
Enzymes possess an active site. The functional group that allows reactant molecules to attach to the active site is a specific shape-defined region of the molecule. The substrate group refers to the molecule that connects to the enzyme. Without the help of a catalyst, the substrate and the enzyme produce an intermediate reaction with low activation energy.
Reactant (1) + Reactant (2) → Product
Reactant (1) + Enzyme → Intermediate
Intermediate + Reactant (2) → Product + Enzyme
The key mechanism of enzymatic activity is to catalyse chemical reactions, which originates with the substrate’s binding to the enzyme’s active site. This active site is a specific area where the substrate interacts.
Also, read: Digestive Enzymes
Enzyme Specificity
The ability of an enzyme to select a specific substrate from a range of chemically similar compounds is known as specificity. Since the enzyme and substrate exhibit complementary structural and conformational properties, specificity is a molecular identification process. Different enzymes exhibit different levels of substrate specificity.
The specificity that enzymes show to the reactions they catalyse is one of the characteristics that makes them so useful as diagnostic and research tools. Only a selected few enzymes can catalyse a single reaction or they have perfect specificity. Other enzymes will have a preference for a certain kind of functional group or chemical bond. There are usually four different categories of specificity:
- Absolute specificity – The enzyme catalyses only one reaction.
- Group specificity – The enzyme acts only on molecules having specific functional groups, like phosphate, amino, and methyl groups.
- Linkage specificity – The enzyme acts on a specific type of chemical bond regardless of the remaining molecular structure.
- Stereochemical specificity – The enzyme acts on a certain optical or steric isomer.
Even though enzymes have high levels of specificity, cofactors can be used by numerous apoenzymes. The reactions of lactate dehydrogenase, malate dehydrogenase, and alcohol dehydrogenase are a few among them. For instance, nicotinamide adenine dinucleotide (NAD) serves as a hydrogen acceptor in a large number of dehydrogenase activities and is a coenzyme for those reactions.
Enzyme Specificity Example
Enzymes vary in their degree of specificity. Due to the specificity of enzyme function, digestive enzymes like pepsin and chymotrypsin can interact with any protein. Thrombin is a component of a very delicate blood-clotting mechanism that can only respond with one substance. This is done to maintain the normal functioning of the system since it only interacts with the protein fibrinogen.
Oxidoreductases do not catalyse reactions involving hydrolysis, and hydrolases do not catalyse processes involving both oxidation and reduction. As a result, an enzyme can catalyse a specific chemical reaction and various substances that are similar to it.
Types of Enzyme Specificity
Only suitably structured molecules may act as substrates for a specific enzyme because the substrate must fit into the active site of the enzyme preceding catalysis. An enzyme will often react with one naturally existing compound. The concept of enzyme specificity will be demonstrated using two oxidoreductase enzymes.
First, alcohol dehydrogenase (ADH) reacts with alcohol, and then lactate dehydrogenase (LDH) reacts with lactic acid. Despite being oxidoreductase enzymes, the two actions are not interchangeable. It indicates that alcohol dehydrogenase cannot catalyse a process involving lactic acid and vice versa. This is because each substrate has a specific structure that makes it impossible to fit into the active site of a different enzyme.
Enzyme specificity is significant since it recognises the various metabolic pathways consisting of a large number of enzymes.
Summary
Specificity is attained when a chemical reactant (the substrate) interacts weakly with an enzyme’s active site to form a bond. The production and dissolution of covalent bonds is the only sort of chemical reaction that an enzyme can catalyse. Reaction specificity, also referred to as absolute reaction specificity, is a property of enzymes that refers to their specificity to a single reaction, meaning that no by-products are produced.
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