Enzymes

The human body is composed of different types of cells, tissues and other complex organs. For efficient functioning, our body releases some chemicals to accelerate biological processes such as respiration, digestion, excretion and a few other metabolic activities to sustain a healthy life. Hence, enzymes are pivotal in all living entities which govern all the biological processes.

What Are Enzymes?

“Enzymes can be defined as biological polymers that catalyze biochemical reactions.”

The majority of enzymes are proteins with catalytic capabilities crucial to perform different processes. Metabolic processes and other chemical reactions in the cell are carried out by a set of enzymes that are necessary to sustain life.

The initial stage of metabolic process depends upon the enzymes, which react with a molecule and is called the substrate. Enzymes convert the substrates into other distinct molecules, which are known as products.

Enzymes are found in all tissues and fluids of the body. Catalysis of all reactions taking place in metabolic pathways is carried out by intracellular enzymes. The enzymes in the plasma membrane govern the catalysis in the cells as a response to cellular signals and enzymes in the circulatory system regulate the clotting of blood. Most of the critical life processes are established on the functions of enzymes.

Enzyme Structure

Enzymes are a linear chain of amino acids, which give rise to a three-dimensional structure. The sequence of amino acids specifies the structure, which in turn identifies the catalytic activity of the enzyme. Upon heating, the enzyme’s structure denatures, resulting in a loss of enzyme activity, which typically is associated with temperature.

Compared to its substrates, enzymes are typically large with varying sizes, ranging from 62 amino acid residues to an average of 2500 residues found in fatty acid synthase. Only a small section of the structure is involved in catalysis and is situated next to the binding sites. The catalytic site and binding site together constitute the enzyme’s active site. A small number of ribozymes exist which serve as an RNA-based biological catalyst. It reacts in complex with proteins.

Enzymes Classification

Earlier, enzymes were assigned names based on the one who discovered them. With further research, classification became more comprehensive.

According to the International Union of Biochemists (I U B), enzymes are divided into six functional classes and are classified based on the type of reaction in which they are used to catalyze. The six kinds of enzymes are:

1. Oxidoreductases: These catalyze oxidation and reduction reactions, e.g. pyruvate dehydrogenase, catalysing the oxidation of pyruvate to acetyl coenzyme A.
2. Transferases: These catalyze transferring of the chemical group from one to another compound. An example is a transaminase, which transfers an amino group from one molecule to another.
3. Hydrolases: They catalyze the hydrolysis of a bond. For example, the enzyme pepsin hydrolyzes peptide bonds in proteins.
4. Lyases: These catalyze the breakage of bonds without catalysis, e.g. aldolase (an enzyme in glycolysis) catalyzes the splitting of fructose-1, 6-bisphosphate to glyceraldehyde-3-phosphate and dihydroxyacetone phosphate.
5. Isomerases: They catalyze the formation of an isomer of a compound. Example: phosphoglucomutase catalyzes the conversion of glucose-1-phosphate to glucose-6-phosphate (phosphate group is transferred from one to another position in the same compound) in glycogenolysis (glycogen is converted to glucose for energy to be released quickly).
6. Ligases: Ligases catalyze the association of two molecules. For example, DNA ligase catalyzes the joining of two fragments of DNA by forming a phosphodiester bond.

Cofactors

Cofactors are non-proteinous substances that associate with enzymes. A cofactor is essential for the functioning of an enzyme. The protein part of enzymes in cofactors is apoenzyme. An enzyme and its cofactor together constitute the holoenzyme.

There are three kinds of cofactors present in enzymes:

1. Prosthetic groups: These are cofactors tightly bound to an enzyme at all times. FAD (flavin adenine dinucleotide) is a prosthetic group present in many enzymes.
2. Coenzyme: A coenzyme binds to an enzyme only during catalysis. At all other times, it is detached from the enzyme. NAD is a common coenzyme.
3. Metal ions: For the catalysis of certain enzymes, a metal ion is required at the active site to form coordinate bonds. Zinc is a metal ion cofactor used by a number of enzymes.

Examples of Enzymes

Following are some of the examples of enzymes:

1. Beverages: Alcoholic beverages generated by fermentation vary a lot based on many factors. Based on the type of the plant’s product, which is to be used and the type of enzyme applied, the fermented product varies.

For example, grapes, honey, hops, wheat, cassava roots, and potatoes depending upon the materials available. Beer, wines and other drinks are produced from plant fermentation.

2. Food Products: Bread can be considered as the finest example of fermentation in our everyday life.

A small proportion of yeast and sugar is mixed with the batter for making bread. Then one can observe that the bread gets puffed up as a result of fermentation of the sugar by the enzyme action in yeast, which leads to the formation of carbon dioxide gas. This process gives the texture to the bread, which would be missing in the absence of the fermentation process.

3. Drug Action: Enzyme action can be inhibited or promoted by the use of drugs which tend to work around the active sites of enzymes.

Functions of Enzymes

The enzymes perform a number of functions in our bodies. These include:

1. Enzymes help in signal transduction. The most common enzyme used in the process includes protein kinase that catalyzes the phosphorylation of proteins.
2. They break down large molecules into smaller substances that can be easily absorbed by the body.
3. They help in generating energy in the body. ATP synthase is the enzyme involved in the synthesis of energy.
4. Enzymes are responsible for the movement of ions across the plasma membrane.
5. Enzymes perform a number of biochemical reactions, including oxidation, reduction, hydrolysis, etc. to eliminate the non-nutritive substances from the body.
6. They function to reorganize the internal structure of the cell to regulate cellular activities.