Enzyme Kinetics

Jul 23, 2024

Enzyme Kinetics Lecture

Introduction

  • Kinetics: Study of reaction rates or speeds.
  • Enzyme Kinetics: Understanding the rate of reactions involving enzymes.
  • Focus is on several key concepts/terms:
    • Michaelis-Menten Equation
    • Graphical representations (Michaelis-Menten plot, Lineweaver-Burk plot)
    • Types of inhibition (competitive, non-competitive, uncompetitive, suicide inhibition)

Michaelis-Menten Equation

Reaction and Derivation

  • Essential reaction: Enzyme (E) + Substrate (S) → Enzyme-Substrate Complex (ES) → Product (P) + Enzyme (E)
  • Rates:
    • K1: Formation of ES
    • K-1: Dissociation into E + S
    • K2: Dissociation into E + P
    • K-2: Negligibly small, considered unidirectional reaction

Steady State Assumption

  • Formation rate of ES = Dissociation rate of ES
  • Graphical representation:
    • Enzyme + Substrate concentration decreases over time
    • Enzyme + Product concentration increases over time
    • Point where ES concentration remains constant

Mathematical Derivation

  1. Set equal rates: K1 [E][S] = K-1 [ES] + K2 [ES]
  2. Total enzyme concentration: E_total = [ES] + [E]
  3. Solve for [E]: [E] = E_total - [ES]
  4. Substitute in the steady state equation.
  5. Simplify using Michaelis constant (Km = (K-1 + K2) / K1)
  6. Derive final Michaelis-Menten Equation: V_0 = (V_max [S]) / (Km + [S])

Key Assumptions

  • Km (Michaelis constant): Substrate concentration at half V_max
  • V_max: Maximum velocity when enzyme is saturated with substrate

Application of Km

  • Relationship to enzyme-substrate affinity:
    • Low Km → High substrate affinity
    • High Km → Low substrate affinity
  • Practical examples:
    • Hexokinase (muscles): Low Km, high affinity
    • Glucokinase (liver): High Km, low affinity

Summary and Important Concepts

  • Derivation Steps: From basic reaction to Michaelis-Menten equation
  • Steady-state assumption: Key to understanding reaction rates
  • Km as an indicator: Affinity of enzyme for substrate

Next Steps

  • Future lectures will cover types of enzyme inhibition and graphical methods like Lineweaver-Burk plot.