Enzyme Function and Inhibition: Key Concepts and Properties

Enzymes

General Properties of Enzymes

Enzymes are biological catalysts that accelerate chemical reactions in living organisms. They are essential for metabolic processes and exhibit remarkable specificity for their substrates.

• Definition: Enzymes are proteins (and some RNA molecules) that catalyze biochemical reactions without being consumed in the process.

• Function: They lower the activation energy required for reactions, increasing the rate of reaction.

• Specificity: Enzymes are highly specific for their substrates due to the unique structure of their active sites.

• Examples: Amylase (breaks down starch), DNA polymerase (synthesizes DNA).

Enzyme Kinetics

Enzyme kinetics studies the rates of enzyme-catalyzed reactions and how they change in response to changes in substrate concentration, enzyme concentration, and the presence of inhibitors.

• Michaelis-Menten Equation: Describes the rate of enzymatic reactions by relating reaction rate to substrate concentration.

$V = \frac{V_{max}[S]}{K_m + [S]}$

• Vmax: Maximum reaction velocity.

• Km: Michaelis constant; substrate concentration at which the reaction rate is half of Vmax.

Enzyme Inhibition

Enzyme inhibitors are molecules that decrease or abolish enzyme activity. They are classified based on their interaction with the enzyme and the effect on enzyme kinetics.

• Competitive Inhibition: Inhibitor resembles the substrate and binds to the active site, preventing substrate binding.

• Noncompetitive Inhibition: Inhibitor binds to a site other than the active site, altering enzyme function without blocking substrate binding.

• Effect on Kinetics:

  • Competitive inhibitors increase Km (apparent decrease in affinity) but do not affect Vmax.

  • Noncompetitive inhibitors decrease Vmax but do not change Km.

$\text{Competitive:} \quad V_{max} \text{ unchanged}, \; K_m \text{ increased}$ $\text{Noncompetitive:} \quad V_{max} \text{ decreased}, \; K_m \text{ unchanged}$

Summary Table: Effects of Inhibitors on Enzyme Kinetics

Type of Inhibition	Effect on Vmax	Effect on Km	Binding Site
Competitive	Unchanged	Increased	Active site
Noncompetitive	Decreased	Unchanged	Allosteric site

Additional info:

• Allosteric Regulation: Some enzymes are regulated by molecules that bind at sites other than the active site, causing conformational changes that affect activity.

• Enzyme Activity: Can be affected by temperature, pH, and the presence of cofactors or inhibitors.