Characteristics of Enzymes

Enzymes are the main group of biological substances required for the proper functioning of cells. They work as a catalyst and perform specific biochemical reactions in living cells. Enzymes were discovered in 1877 by Wilhelm Friedrich Kühne a professor of physiology at the University of Heidelberg. He coined the term enzyme for such biological substances. To date, 10,000 enzymes have been discovered by scientists. 

Diagram of enzyme and substrate created in BioRender.com

Read about types of enzyme inhibition and factors affecting enzyme catalysis.

Characteristics of enzymes 

Enzymes possess specific characteristics which are discussed in detail below.

1. Nature of enzyme

Enzymes are protein in nature. Each enzyme has a specific sequence of amino acids that fold upon themselves to form a specific globular structure. Recently, some catalytic RNAs (ribozymes) have been reported to be displaying enzymatic activities e.g., hammerhead ribozyme.

2. Increases rate of reaction and lower the activation energy

Enzymes act as a catalyst and increase the rate of chemical reactions by lowering the activation energy. Activation energy is the energy required by substances to carry out a chemical reaction. The rate of reaction increases when activation energy decreases. The rate of enzyme-catalyzed chemical reactions increases from 100 million to 10 billion compared to regular chemical reactions.

3. Not consumed during chemical reaction

Enzymes are not consumed during the chemical reactions. The bonds between amino acids might break down or new bonds with the substrate are formed during the attachment of the enzyme to the substrate. But the quantity of enzyme at the start and end of chemical reaction remains the same.

4. Small quantity is required

A minute amount of enzymes are required to perform chemical reactions. A typical enzyme is capable of catalyzing 100-10,000 substrates into products per second.

5. Specific classes of enzymes

Enzymes are specific in their actions and catalyze only specific chemical reactions. They are divided into six classes by the International Union of Biochemists (I U B) based on reactions performed by them. These classes are lyases, oxidoreductases, hydrolases, ligases, transferases, and isomerases.

6. Does not effect other chmeical reactions

As enzymes are specific for their reactions, so their presence in a cell does not affect other chemical reactions.

7. Optimum temperature

Enzymes perform to their maximum at a specific temperature known as optimum temperature. Any change in optimum temperature might lead to a decrease in the activity of that enzyme. For example, enzymes in the human body work properly at 37 °C.

8. Optimum pH

Enzyme activity is also dependent on the pH of the medium. The pH at which the enzyme performs its maximum function is called optimum pH. Any variation in optimum temperature might lead to denaturation of the enzyme. For example, the optimum pH for enzymes in the human body is 7.35 to 7.45, except stomach which has an optimum pH of 1.5.

9. Enzymes are substrate-specfic

Enzymes are larger as compared to the substrate and have a specific site called an active site for the binding of substrate. The shape of the active site is specific for a specific substrate. Due to which enzymes are substrate-specific. For example, the pepsin enzyme present in the stomach is specific for the digestion of proteins and cannot digest lipid or carbohydrates.

10. Cofactor needed

Some enzymes require co-factor for their proper functioning. Cellular respiration is an enzyme-catalyzed chemical reaction. Enzymes involved in this reaction require two cofactors NAD+, and FAD+ for their proper functioning.

11. Enzymes can be inhibited

The catalytic activity of enzymes can be inhibited by the addition of certain substances known as inhibitors. There are three types of inhibitors i.e., irreversible, competitive, non-competitive inhibitors. An irreversible inhibitor makes the enzyme inactive. Competitive inhibitor competes with the substrate and binds with the enzyme ate active site thus inhibits enzyme activity, while non-competitive inhibitor binds enzyme other than the active site.

12. Saturation level

Enzyme activity can be increased by increasing the amount of substrate until the saturation level is reached. After that increase in the substrate will not increase the reaction rate because all the active sites will be occupied with the substrate at that point.

13. Inactive form of enzymes

Some enzymes are synthesized in an inactive form until they reach their site of activity and then converted into active form e.g., pepsin enzyme is initially produced as pepsinogen which is the inactive form.

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Some questions and answers

Q. How enzymes decrease activation energy?
A. Enzymes lower the activation energy by adjusting the orientation of the substrate or changing their charges.

Q. What is the optimum temperature of enzymes present in a human body?
A. The enzymes in the human body work properly at 37 °C.

Q. What is the optimum pH of pepsin and salivary amylase?
A. The optimum pH of pepsin is 1.0–2.0, while salivary amylase works best at optimum pH of 6.7–7.0.

Q. Why the rate of reaction becomes stable after the saturation point of the enzyme?
A. At the saturation point of the enzyme, all the active sites are occupied by the substrates, so new substrates cannot be accommodated or converted into products by the enzymes. Hence, the rate of reaction becomes stable.

Q. Why some enzymes are produced in inactive form?
A. Some enzymes are produced in an inactive form to protect the organs from damage. For example, the pepsin enzyme is initially produced as pepsinogen which is the inactive form and then sent to the stomach where it is converted into active form pepsin. If it is not produced in the inactive form then it will start digesting the glands that produced it.

Q. What are the three main characteristics of an enzyme?
A. Enzymes increase the rate of reaction by lowering the activation energy, they are not consumed during a chemical reaction and are required in small quantities.

References

• Gurung, N., Ray, S., Bose, S., & Rai, V. (2013). A broader view: microbial enzymes and their relevance in industries, medicine, and beyond. BioMed research international, 2013.
• Schwalfenberg, G. K. (2012). The alkaline diet: is there evidence that an alkaline pH diet benefits health?. Journal of environmental and public health, 2012.
• Boyer, P. D., & Krebs, E. G. (1986). The enzymes. Academic Press.
• Chen, K., & Arnold, F. H. (2020). Engineering new catalytic activities in enzymes. Nature Catalysis, 1-11.