Enzyme Kinetics and Inhibition

Overview

• Review of enzyme inhibition types: competitive, non-competitive, uncompetitive, and suicide inhibition.
• Introduction to the Michaelis-Menten equation.
• Explanation of the Michaelis-Menten curve (rectangular hyperbola) and the Line-Weaver-Burke plot (linear form).

Michaelis-Menten Curve

• Axes:
  • X-axis: Substrate concentration.
  • Y-axis: Reaction velocity (V₀).
• First-order kinetics:
  • Linear region of the curve where velocity increases proportionally with substrate concentration.
• Zero-order kinetics:
  • Plateau phase where increasing substrate concentration does not change velocity.
  • Occurs when enzyme is saturated (Vmax).
• Vmax: Maximal velocity when enzyme is fully saturated with substrate.
• Km: Substrate concentration at half Vmax.

Types of Inhibition

• Competitive Inhibition:
  • Increases Km.
  • No effect on Vmax.
  • Requires higher substrate concentration to reach Vmax.
• Non-competitive Inhibition:
  • No effect on Km.
  • Decreases Vmax.
  • Cannot reach Vmax even with increased substrate concentration.
• Uncompetitive Inhibition:
  • Decreases both Km and Vmax.
  • Shifts curve to the left and down.

Line-Weaver-Burke Plot

• Axes:
  • Y-axis: 1/V₀.
  • X-axis: 1/[Substrate concentration].
• Intercepts and Slopes:
  • Y-intercept: 1/Vmax.
  • X-intercept: -1/Km.
  • Slope: Km/Vmax.

Inhibition Effects on Line-Weaver-Burke Plot

• Competitive Inhibition:
  • Increases Km: shifts x-intercept to the right.
  • Slope increases.
• Non-competitive Inhibition:
  • Decreases Vmax: raises y-intercept.
  • Slope increases.
• Uncompetitive Inhibition:
  • Decreases both Km and Vmax.
  • Shifts both intercepts.
  • Slope remains parallel.

Summary

• Competitive increases Km and affects x-intercept and slope.
• Non-competitive decreases Vmax and affects y-intercept and slope.
• Uncompetitive decreases Km and Vmax, affects both intercepts.
• No inhibition follows normal enzyme kinetics.