Enzymes are proteins that act by controlling speed and regulating the reactions that occur in the body. They catalyze specific chemical reactions acting on specific substrates and at specific locations on those substrates.

The action of enzymes can be influenced by some factors, such as high temperature. Below we will talk a little more about them, their importance, their mechanism of action, and their nomenclature and classification.

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What are enzymes?

Enzymes are specialized globular proteins that act by controlling speed and regulating the body’s chemical reactions. It is important to note that some RNA molecules , known as ribozymes , act as enzymes. These still have a catalytic role, that is, they act by increasing the speed of chemical reactions.

Enzymes have a three-dimensional structure, and their activity depends on the characteristics of the environment in which it is found.

Enzymes are highly specific , each of which acts on a specific substrate in a reaction. Currently, more than 2,000 enzymes are known, and each one acts in a specific reaction.

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Enzyme nomenclature

Enzyme nomenclature occurs in several ways. The three most used forms are:

  • Classic or recommendedname : usually names, adding the -ase termination to the name of the substrate on which the enzyme acts. This is the form most used by those who work with enzymes. For example, the amylase enzyme acts in the hydrolysis reaction of starch in glucose molecules , and urease catalyzes the urea hydrolysis reaction in ammonia and CO
  • Usual name:uses names consecrated by use, such as trypsin and pepsin.
  • Systematic name:more complex form and instituted by the International Union of Biochemistry and Molecular Biology (IUBMB), it presents more information than the others regarding the functionality of the enzyme. The systematic name generally has three parts: the name of the substrate, the type of catalyzed reaction and the suffix -ase For example, the reaction of converting glucose-6-phosphate to fructose-6-phosphate is catalyzed by the enzyme called glucose phosphate isomerase. In addition to the systematic name, the enzyme also receives a number, which must be used for accurate identification. This numbering follows the model: EC XXXX. The acronym EC represents the Enzyme Commission (Enzyme Commission) of the International Union of Biochemistry and Molecular Biology, and the sequence of four numbers refers to its classification.

Classification of enzymes

Enzymes can be classified according to the International Union of Biochemistry and Molecular Biology and according to the type of reaction they catalyze , as follows:

Class 1. Oxide-reductases: oxide-reduction reactions or electron transfers (hydride ions or H atoms). Examples: dehydrogenases and peroxidases.

Class 2. Transferases: reactions of transfers of functional groups between molecules. Examples: aminotransferases and kinases.

Class 3. Hydrolases: hydrolysis reactions, in which a molecule breaks down into smaller molecules with the participation of water. Examples: amylase, pepsin and trypsin.

Class 4. Liases: reactions in which the addition of groups to double bonds or the removal of groups leaving a double bond may occur. Example: fumarase.

Class 5. Isomerase: reactions in which the formation of isomers occurs. Example: epimerase.

Class 6. Ligase: synthesis reactions in which molecules join with energy expenditure, usually from ATP . Example: synthetases.

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Mechanism of action of enzymes

Enzymes work by binding to specific substrates at specific locations. At the end of the process, they are released to catalyze new reactions.

The energy required for a reaction to start is called activation energy . Enzymes work by reducing this activation energy and causing the reaction to occur faster than in the absence of it. This catalytic capacity of the enzymes increases the speed of the reactions by about 10 14 times.

The action of enzymes occurs through their temporary association with the molecules that are reacting, bringing them closer together. As a result, enzymes can also weaken existing chemical bonds, facilitating the formation of new bonds. They bind to specific molecules, called substrates , and in specific places, the activation sites, forming a transient complex. At the end of the process, this complex decomposes, releasing the products and the enzyme, which usually recovers its shape and can be used again to catalyze reactions.

The enzymes act in a chain, and several of them can act in sequence, in a certain set of reactions, forming the so  called metabolic pathways . A cell has several metabolic pathways, each responsible for a specific function, for example, the synthesis of substances, such as amino acids .

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Connecting sites

As stated, enzymes bind to substrates at so-called binding sites . They have specific amino acid residues arranged in a three-dimensional form, forming the binding sites, places where the substrates bond during the reaction.

In addition to this three-dimensional arrangement , the enzymes present, in these sites, an appropriate arrangement of hydrophilic (interact with water) and hydrophobic (do not interact with water), charged (have electric charges) and neutral (do not have electric charges) regions .

The substrate must have an adequate , structural and chemical configuration , in order to be lodged in the connection site. This perfect-fit model is known as a key-lock model , due to the relationship with the fact that each key fits a specific lock. However, it is known that the approach and binding of the substrate to the binding site induces a conformational change in the enzyme, making it ideal. This model is known as the induced fit model .

Factors that regulate enzyme activity

The enzymes can have their activity influenced by many factors. Among these we can highlight the temperature, the pH and are regulatory enzymes.

  • Temperature :Most enzymes increase their reaction rates as the temperature at which they act increases by 10 ºC. However, this rate starts to decline as soon as the temperature reaches 40 ºC. From that temperature, it is observed that the enzymes start to undergo denaturation, an unfolding of their structure.
  • pH :Changes in the pH of the medium in which the enzyme is found leads to changes in its loads. The maintenance of the form of the enzymes is due to the attraction and repulsion between the charges of the amino acids that constitute it. Changes in these charges alter the shape of the enzyme, affect the bond between it and the substrate and thus its functionality.
  • Regulatory enzymes :These act by regulating the rate of metabolic pathways. Often, they occupy the first place in the sequence of the metabolic pathway and increase or decrease the activity through some signals, such as the substrate levels or the energy demand of the cell .

Enzyme Summary

  • Enzymes are proteins that act as biological catalysts.
  • Catalysts are substances that act by decreasing the activation energy of reactions, increasing the speed at which they occur and not being consumed in the process.
  • Enzymes have high specificity, acting only on specific substrates.
  • Enzymes work by decreasing the activation energy of reactions in cells.
  • Temperature, pH and regulatory enzymes are factors that influence enzyme activity.


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