6. ENZYMES

ENZYMES: A TEACHER’S COMPREHENSIVE GUIDE

Welcome, future pharmacists and healthcare professionals!

Enzymes are biological catalysts that are virtually usually proteins. It accelerates the pace of a certain chemical process in the cell. The enzyme is not damaged during the process and may be utilised repeatedly. A cell includes hundreds of distinct types of enzyme molecules, each tailored to a specific chemical process. Enzymes are normally proteins, although they can also be RNA. The term “enzyme” is derived from Greek, which means “in yeast” because the yeast cells were the first to disclose enzyme activity in living organism.

Dpharmguru’s exam insights:

In my years of teaching biochemistry, I have observed that students often get confused between enzymes and other proteins. Remember: Enzymes are biological catalysts that speed up reactions without being consumed. James Sumner first crystallised urease in 1926 and proved that enzymes are proteins. This is a very common exam question!

PROPERTIES OF ENZYMES

• All enzymes are proteins, except the group of catalytic RNAs.
• The molecular weight of enzyme ranges from 12,000 to 1 million or more.
• The catalytic activity of enzymes is mainly due to the primary, secondary, tertiary, and quaternary structures of protein.
• Most enzymes require only amino acid residue to show their effect, whereas some enzymes need cofactor or coenzyme.
• Holoenzymes are the catalytically active enzymes, made up of coenzyme or metal ions (non-protein part) and apoenzyme (protein part).
• Enzymes are required in very minute quantity. They are not consumed in the overall enzymatic reaction.

Dpharmguru’s exam insights:

Remember the difference between apoenzyme and holoenzyme: Apoenzyme = protein part only (inactive), Holoenzyme = apoenzyme + cofactor (active). This is a frequently tested concept!

IUB CLASSIFICATION OF ENZYMES

Dpharmguru’s exam insights:

Remember the six classes of enzymes with a mnemonic: “Over The Hill, Ladies Love Ice-cream” — Oxidoreductases, Transferases, Hydrolases, Lyases, Ligases, Isomerases. This is a classic exam question!

MECHANISM OF ENZYME ACTION

Active Sites

The substrate-binding place of an enzyme at which catalysis occurs is known as the active site. This site is a cleft or big pocket-shaped structure surrounded by amino acids. The catalytic as well as the binding sites are contained by the active site of an enzyme. The chemical properties, as well as, the structure of the active site allow substrate binding and recognition.

Enzyme Specificity

• Bond Specificity: Selective to substrates acquiring similar bonds and structures. Example: α-amylase hydrolyses α-1-4 glycosidic linkages.
• Group Specificity: Specific to a bond and the groups that surround the bond. Example: Pepsin, Trypsin, Chymotrypsin.
• Substrate Specificity: Only one substrate and one reaction are particular. Example: Lactase hydrolyses lactose; Maltase hydrolyses maltose.
• Optical Specificity: Specific to the optical configuration of substrate. Example: L-amino acid oxidase works on L-amino acids.
• Geometrical Specificity: Single enzyme can work on substrates with similar molecular shapes. Example: Alcohol dehydrogenase oxidises both ethanol and methanol.
• Co-factor Specificity: Enzymes that require co-factors to function.

Enzyme-Substrate Complex Formation

• Lock and Key Model: Proposed by Emil Fischer in the 1890s. The active site of the enzyme allows the substrate to exactly fit in.
• Induced Fit Model: Proposed by D. Koshland in 1966. The active site of an enzyme is flexible, not rigid. The shape of the enzyme changes to accommodate the substrate.

Lowering of Activation Energy

Enzymes lower the activation energy required for a reaction to proceed. The energy of activation (E) in the presence of an enzyme is lowered, allowing the reactant to be converted to product with lower energy requirements.

FACTORS AFFECTING ENZYME ACTIVITY

• Enzyme Concentration: Reaction rate is directly proportional to enzyme concentration.
• Substrate Concentration: Reaction velocity is directly proportional to substrate concentration up to a maximum (Vmax).
• Product Concentration: Enzyme activity declines on accumulation of reaction products.
• Temperature: Optimum temperature for most enzymes is between 40-45°C. Higher temperature causes denaturation.
• pH: Optimal activity of most enzymes is between pH 5 to 9. Extreme pH causes inactivation.
• Inhibitors and Activators: Inhibitors decrease catalytic activity; activators increase catalytic activity.
• Time: Less time required under ideal and optimal conditions.
• Light and Radiation: X-rays, gamma rays, UV and beta rays can denature enzymes.

Effect of Temperature and pH

Optimum temperature is the temperature at which enzyme is optimally active. For most enzymes, it is between 40-45°C. Optimum pH is the pH possessed by each enzyme at which velocity of enzyme is maximum.

Dpharmguru’s exam insights:

A common exam question is: “What is the optimum temperature for most human enzymes?” The answer is 37°C (body temperature). Also, enzymes become denatured at temperatures above 50°C, and extreme pH causes irreversible denaturation.

ENZYME INHIBITORS

1. Reversible Inhibition

• Competitive Inhibition: Inhibitor competes with substrate for the active site. Vmax remains constant, Km increases.
• Non-competitive Inhibition: Inhibitor binds at a site distinct from the active site. Vmax decreases, Km remains constant.
• Uncompetitive Inhibition: Inhibitor binds only to the enzyme-substrate complex.

2. Irreversible Inhibition

Irreversible inhibitors form covalent bonds with the amino acid residue present near or at the active site. This inactivates the enzyme permanently. Examples: DIPF (nerve gas), Iodoacetamide, Penicillin.

3. Allosteric Inhibition

Allosteric inhibition refers to the inhibition of an enzyme activity by the so-formed end product in the pathway. Allosteric inhibitors act on the enzyme’s allosteric site.

Dpharmguru’s exam insights:

Remember the difference between competitive and non-competitive inhibition: In competitive inhibition, the inhibitor competes for the active site (Vmax same, Km increases). In non-competitive inhibition, the inhibitor binds elsewhere (Vmax decreases, Km same). This is frequently tested!

THERAPEUTIC AND PHARMACEUTICAL IMPORTANCE OF ENZYMES

Therapeutic Enzymes and their Uses

Pharmaceutical Enzymes and their Uses

Important Enzymes in the Diagnosis of Diseases

Dpharmguru’s exam insights:

Enzymes are the catalysts of life. In exams, pay special attention to: (1) The six classes of enzymes, (2) The lock and key vs induced fit models, (3) The factors affecting enzyme activity (temperature, pH, substrate concentration), (4) The types of enzyme inhibition (competitive vs non-competitive), and (5) The diagnostic and therapeutic uses of enzymes. Remember: “Enzymes are the workers of the cell!”

REFERENCES AND FURTHER READING

• Lehninger, A. L., Nelson, D. L., & Cox, M. M. (2017). Lehninger Principles of Biochemistry (7th ed.). W. H. Freeman.
• Berg, J. M., Tymoczko, J. L., & Stryer, L. (2019). Biochemistry (9th ed.). W. H. Freeman.
• Satyanarayana, U., & Chakrapani, U. (2021). Biochemistry (5th ed.). Elsevier.
• Vasudevan, D. M., Sreekumari, S., & Vaidyanathan, K. (2022). Textbook of Biochemistry for Medical Students (9th ed.). Jaypee Brothers.
• National Institutes of Health (NIH). (2022). Enzyme Resources. Retrieved from https://www.nih.gov.

Disclaimer: This article is for educational purposes only and does not constitute medical advice. Always consult qualified healthcare professionals for medical concerns.

written by:
Dr. N. Sujith Kumar

Dr. N. Sujith Kumar is a pharmacy educator, Pharm.D graduate, and academic content creator from Jawaharlal Nehru Technological University Kakinada (JNTUK), where he completed his Doctor of Pharmacy (Pharm.D) degree between 2015 and 2021. He has more than 7 years of experience creating pharmacy educational content, writing study materials, and reviewing academic articles for pharmacy students. He has also contributed guest articles to pharmacy education platforms, including PharmD Guru. At D.PharmGuru, his work focuses on simplifying complex Diploma in Pharmacy (D.Pharmacy) subjects into easy-to-understand notes, practical explanations, and exam-oriented educational resources for students across India. His areas of focus include Human Anatomy and Physiology, Pharmaceutics, Pharmacology, Pharmaceutical Chemistry, Hospital and Clinical Pharmacy, and other core D.Pharmacy subjects.