Enzyme: Structure, Function, and Factors Affecting Activity

Enzymes are biological catalysts that play a crucial role in facilitating chemical reactions within living organisms. They have the ability to accelerate the rate of reactions without being consumed in the process.

1. Structure of Enzymes:

• Simple enzymes: Consist solely of proteins.

• Complex enzymes: Composed of a protein component (apoenzyme) and a non-protein component (coenzyme).

• Coenzyme: An organic compound, often containing vitamins, that acts as a carrier of chemical groups, electrons, or hydrogen ions.

• Holoenzyme: The complete enzyme consisting of both the apoenzyme and coenzyme.

2. Function of Enzymes:

• Catalyze biochemical reactions: Enzymes accelerate the rate of reactions by lowering the activation energy required for the reaction to occur.

• Specificity: Each enzyme catalyzes only a specific type of reaction or a specific group of reactions.

3. Factors Affecting Enzyme Activity:

• Temperature: Each enzyme has an optimal temperature (T° optimum) at which it exhibits maximum activity. Temperatures higher than the optimum can denature the enzyme, leading to loss of activity.

• pH: Each enzyme has an optimal pH for activity. Variations in pH from the optimum can decrease enzyme activity.

• Substrate concentration: As substrate concentration increases, the reaction rate increases until it reaches a maximum rate (Vmax).

• Enzyme concentration: Increasing enzyme concentration increases the reaction rate.

• Activators: Substances that enhance enzyme activity.

• Inhibitors: Substances that decrease enzyme activity.

4. Types of Enzyme Inhibitors:

• Non-specific inhibitors: Affect any protein molecule, causing denaturation, and are often irreversible.

• Specific inhibitors: Target a specific enzyme. There are two types:

• Competitive inhibitors: Compete with the substrate for binding to the active site of the enzyme.

• Non-competitive inhibitors: Bind to the enzyme at a site other than the active site, altering the enzyme’s structure and reducing its activity.

5. Enzyme Classification:

Enzymes are classified into six classes based on the type of chemical reaction they catalyze:

1. Oxidoreductases: Catalyze oxidation-reduction reactions.

2. Transferases: Catalyze the transfer of functional groups from one molecule to another.

3. Hydrolases: Catalyze hydrolysis reactions, using water to break chemical bonds.

4. Lyases: Catalyze the removal of a functional group from a molecule, forming a double bond or ring.

5. Isomerases: Catalyze reactions that convert the structural isomer of a molecule.

6. Ligases (synthetases): Catalyze the joining of two molecules, utilizing energy from ATP.

6. Some Typical Enzymes:

• Amylase: Breaks down starch into maltose.

• Pepsin: Digests proteins in the stomach.

• Trypsin: Digests proteins in the small intestine.

• Lipase: Breaks down lipids into glycerol and fatty acids.

• Acid phosphatase: Found in the prostate gland, catalyzes the hydrolysis of phosphate ester bonds.

• Alkaline phosphatase: Found in bones and liver, catalyzes the hydrolysis of phosphate ester bonds.

Note:

• The substrate concentration required for the reaction rate to reach half its maximum value is known as the Michaelis-Menten constant (Km).

• A larger Km indicates a lower affinity of the substrate for the enzyme.

• Allosteric enzymes have two sites: the active site and the allosteric site.

• Positive allosteric effectors activate the enzyme.

• Negative allosteric effectors inhibit the enzyme.

• Different molecular forms of the same enzyme are called isoenzymes.

• Inactive forms of enzymes are called zymogens, proenzymes, or preenzymes.

• Ubiquinone is a coenzyme involved in oxidation-reduction reactions.

• Coenzyme NAD+, NADP+ function in a dissolved state.

Conclusion:

Enzymes are crucial biological catalysts that play essential roles in the biochemical processes of living organisms. Understanding their structure, function, and the factors influencing their activity provides insights into the mechanisms of cellular processes and enzyme-related diseases.