Enzymes

Enzymes could be defined as catalysts found in living cells, constituted by protein substances, that help facilitate complex biochemical and metabolic reactions. As a virtue of being catalysts, enzymes do not directly participate in the biological reactions but aid their efficient occurrence. Thus, an enzyme could be brought to use often without being exhausted.

A few examples are Protease (an enzyme that helps break down protein into its simpler components), Proteases (a class of enzymes that help break down proteins into their constituent amino acids) 

Lipase(an enzyme that helps break down fat into its simpler constituents), amylase(that breaks down starch into glucose to aid energy production in the digestion process) and Lactase(an enzyme that works on Lactose, a major constituent of milk and as a result, dairy products such as curd, cheese etc). 

Enzymes are formed when a certain number (which means, at least a thousand) of amino acids are linked together in chains with the help of amide or peptide bonds. Enzymes are commonly added in beverages, chocolates, bread, curd, pre-digested baby food, washing powders etc. to aid their efficient preparation and effect. 

Enzyme Structure

Enzymes are made up of several amino acids and hence are structured the same as proteins. The enzyme consists of an active site or a substrate binding site. This site is where the substrate get attached and the chemical reaction takes place. The enzyme can break a bigger molecule to simpler ones or vice versa. 

The enzyme also contains a site other than the substrate binding site called the allosteric site or inhibitor site. The inhibitor site is functional when the enzyme is in inactivated stage. If the inhibitor site is filled by inhibitor in the enzyme, the shape of the active site is changed and therefore does not allow any substrate to get attached to the active site and does not process any further reaction. 

Enzymes have what biologist Emil Fisher, in 1984, described as the lock and key structure model. Enzymes, according to Fisher, are shaped in a certain way whereas the corresponding structures, called substrates have a shape that can fit into the enzyme’s “active site” like a key does in a lock. This is also one of the reasons why enzymes are found to be so specific in their working. The lock and key model, proposed by Emil Fisher could be understood with the help of the following diagram:

In 1958, another scientist by the name of Daniel Koshland proposed a theory that suggested the active sites of enzymes to be flexible and modifiable and hence, could be reshaped by interactions with the corresponding substrates. In certain cases, Koshland believed, the substrate might also modify its shape to fit the enzyme. This theory is known as the “Induced Fit Hypothesis”. This happens when enzymes such as glycosidases function. The mechanism of the working of the enzyme, as described above, could be understood by the following figure depicting the working of the Induced 

Fit Model of the Enzyme:

The general equation that could describe the working of an enzyme through the enzyme-substrate reaction is as follows:

Substrate + Enzyme = (Substrate-Enzyme) > (Product-Enzyme or Intermediate) = Product + Enzyme. 

The enzyme-substrate interaction can better be explained by a lock and key mechanism. The substrate is the key and the enzyme is the lock. Each substrate is specific to its enzyme, same as how every key is specific to its lock. For example, a lactose molecule will only bind to a lactase enzyme because it has the substrate binding site which is specific to the substrate also called as active site. After the substrate is bound to the enzyme, the reaction takes place where old bonds are broken and new bonds are formed, hence making a new molecule. This new molecule is the product. The reaction if taken place without an enzyme would consume high amount of activation energy, but with the presence of enzyme consumes relatively less energy. 

The classification of an enzyme, is done keeping in mind its function, that makes it liable to fit in one of the following six categories, all ending with the suffix “ase”-

  • First, Oxidoreductases. These are enzymes that catalyze oxidation-reduction reactions by facilitating electron transfers. The electrons that these oxidoreductases help transfer are generally hydride ions or hydrogen atoms. 

  • Second, Transferases.  Transferases are enzymes that facilitate group transfer processes wherein a molecule is a donor while another molecule poses as an acceptor. This transfer of certain substances is aided by transferases, 

  • Third, Hydrolases. These are enzymes that help in hydrolysis(the chemical degeneration of compounds, as a result of reaction with water). 

  • Fourth, Lyases. Lyases are enzymes that aid in processes where functional groups are added to break double bonds within molecules or get rid of functional groups by formation of double bonds within molecules. 

  • Fifth, Ligases. These enzymes are required when there has to be carbon-carbon, carbon-nitrogen, carbon-sulfide, or carbon-oxygen bond formation. 

  • Sixth, Isomerases. Isomerases, as the name might suggest, help formulate isomeric forms of compounds. This process of interconversion involves active oxidation and reduction. 

There are Several Factors Affecting Enzyme Activity. 

  • The correct temperature for enzyme functioning is very crucial. Temperature above a certain limit can destroy the enzyme completely and lead it to disintegrate, rendering it useless. This process is termed as denaturation. 

  • So is the correct extent of acidic, basic or neutral environment. For instance, the enzyme pepsin is the most efficient when working in an environment of 1.5 pH.  

  • Certain vitamins and other non-protein substances, in humans and animals, might act as “co-factors” that help the enzyme to work efficiently by aiding the binding process. Presence or absence of these cofactors also affects the working of an enzyme-making it slower, quicker, incomplete or efficient.

  • Substances called inhibitors could be used to stop a substrate from binding to an enzyme’s active site and hence, the presence of an inhibitor is a factor that could prove dire to the functioning of an enzyme. 

  • Enzyme concentration is a major factor that effects the reaction. The more enzymes present in the reaction, more substrate is transformed into product and less time is consumed for the reaction to take place. 

  • Substrate concentration is also a factor where if the substrate is low, the reaction rate is also low, but if substrate is increased steadily, the reaction rate also increases. But if the amount of substrate exceeds the amount of enzymes then the reaction rate remains constant, and the velocity of the enzyme is maximum. This velocity is called Vmax, which the maximum velocity obtained by the enzyme in the presence of excess substrate. 

Action and Nature of Enzymes

  • As already mentioned, enzymes are protein in nature and are made up of several amino acids. 

  • They are formed by the exocrine glands and paracrine glands and are transferred to the required place through ducts. 

  • Enzymes are basically catalyst which fastens the chemical reaction in the body. 

  • Enzymes lowers the activation energy required for a chemical reaction and hence, less energy is required to carry a reaction forward.