Enzymes – The Biological Catalysts

🔹 Introduction

Enzymes are protein-based biological catalysts that significantly accelerate biochemical reactions by reducing the activation energy required. While most enzymes are proteins, a few catalytic RNA molecules, known as ribozymes, also perform enzymatic functions. These molecules are central to various physiological processes including digestion, biosynthetic pathways, cellular respiration, DNA replication, signal transduction, and tissue repair. Without enzymes, cellular metabolism would proceed too slowly to sustain life.

🔹 Properties of Enzymes

• Substrate Specificity: Enzymes exhibit a high degree of specificity, acting only on particular substrates or types of bonds, enabling tightly regulated metabolic pathways.
• Catalytic Efficiency: They can increase reaction rates by up to 10⁶-fold, making them highly efficient even at low concentrations.
• Reusability: Since enzymes are not consumed during reactions, they can catalyze multiple cycles of transformation.
• Environmental Sensitivity: Enzymatic activity is highly sensitive to variables such as temperature, pH, substrate concentration, and ionic strength.
• Regulatory Potential: Enzymes are subject to allosteric regulation, feedback inhibition, and covalent modifications, allowing fine-tuned control of metabolic fluxes.

🔹 Structure of Enzymes

Enzymes are composed of polypeptide chains folded into specific tertiary or quaternary structures stabilized by non-covalent interactions. Their functional region, the active site, binds to substrates through shape complementarity and intermolecular forces. Some enzymes require cofactors (inorganic ions) or coenzymes (organic molecules) to function. The enzyme-substrate complex is a transient structure critical for catalysis.

🔹 Classification of Enzymes (IUBMB System)

1. Oxidoreductases: Catalyze redox reactions (e.g., dehydrogenases).
2. Transferases: Transfer functional groups like methyl or phosphate (e.g., transaminases).
3. Hydrolases: Break bonds via hydrolysis (e.g., proteases).
4. Lyases: Add/remove atoms, often forming double bonds (e.g., decarboxylases).
5. Isomerases: Rearrange atoms within a molecule (e.g., isomerases).
6. Ligases: Join molecules using ATP (e.g., DNA ligase).

🔹 Mechanism of Enzyme Action

• Lock and Key Model: Substrate fits the enzyme’s active site precisely.
• Induced Fit Model: Enzyme adjusts its shape to better fit the substrate.

The enzyme-substrate complex transitions through a high-energy intermediate and releases the product. Enzymes reduce activation energy by stabilizing this transition state.

🔹 Factors Affecting Enzyme Activity

• Temperature: Optimal around 37°C in humans. High heat may denature enzymes; low temperatures reduce activity.
• pH: Each enzyme has a specific pH range. Example: Pepsin (acidic), amylase (neutral).
• Substrate Concentration: Activity increases with concentration up to saturation (V_max).
• Inhibitors:
  • Competitive: Compete with substrate for the active site.
  • Non-competitive: Bind allosterically, altering enzyme shape.
  • Uncompetitive: Bind only to the enzyme-substrate complex.

🔹 Enzyme Inhibition

Reversible inhibition involves non-covalent interactions and includes competitive, non-competitive, and uncompetitive mechanisms. Irreversible inhibitors form covalent bonds or bind tightly to enzymes, permanently disabling their function (e.g., cyanide, heavy metals). These concepts are essential in pharmacology and metabolic regulation.

🔹 Coenzymes and Cofactors

• Cofactors: Inorganic ions (e.g., Mg²⁺, Zn²⁺, Fe²⁺) aiding in catalysis or structure.
• Coenzymes: Organic molecules derived from vitamins (e.g., NAD⁺ from niacin, FAD from riboflavin) that assist in electron and group transfer.

🔹 Applications of Enzymes

Medical Field

• Diagnostic enzymes (e.g., glucose oxidase in glucometers).
• Enzyme replacement therapies (e.g., for Gaucher’s disease).
• Therapeutic uses: wound debridement, cancer treatment.

Industrial Applications

• Food processing: baking, brewing, cheese making.
• Detergents: stain removal (proteases, lipases).
• Textiles and paper: eco-friendly bleaching and bio-finishing.

Agriculture

• Promote soil fertility and organic decomposition.
• Aid composting and biocontrol.

Biotechnology and Research

• Enzymes like Taq polymerase used in PCR.
• Restriction enzymes, ligases essential in genetic engineering.

🔹 Summary

Enzymes are essential biomolecules in life and technology. Their precision, catalytic speed, and regulatory control make them crucial for metabolic regulation, drug design, biotechnology, and industrial innovation. A strong understanding of enzyme science is fundamental in life sciences and applied research.

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