Enzyme Kinetics and the Michaelis-Menten Equation

Introduction

• Previous Topics Covered:
  • Properties of enzymes
  • Nomenclature or classes of enzymes
  • Mechanisms of enzyme activity
  • Two theories: Key and Lock Theory, Induced Fit Theory
• Current Topic: Enzyme kinetics, focusing on the Michaelis-Menten equation and related graphs.

Enzymes Overview

• Enzymes are proteins that act as catalysts.
  • Speed up reactions by lowering activation energy.
  • Do not change equilibrium or overall free energy.
  • Enzymes have specificity for their substrates (Affinity).

Key Enzyme Concepts

• Kinases and Phosphatases:
  • Kinases transfer phosphates (transferases).
  • Phosphatases remove phosphates by hydrolysis (hydrolases).
• Active Site vs. Allosteric Site:
  • Active site: Occupied by substrate; enzyme-substrate complex formed.
  • Induced Fit Model: Substrate binding changes enzyme shape.

Michaelis-Menten Equation

• Graph Interpretation:
  • Direct relationship between substrate concentration and initial reaction velocity.
  • Plateau occurs due to enzyme saturation.
• Mathematical Relationships:
  • Direct relationships when entities are divisible or subtractable.
  • Inverse relationships when entities are multiplicable or additive.

Saturation and Vmax

• Enzymes get saturated with high substrate concentration, leading to Vmax.
• Facilitated Diffusion Analogy:
  • Carrier proteins become saturated; similar to enzyme saturation.

Km and Affinity

• Km (Michaelis Constant):
  • Represents substrate concentration at half Vmax.
  • Related inversely to enzyme affinity.

Practical Implications

• Enzymes' maximum velocity (Vmax) is theoretical; practical focus on half Vmax.
• Relevance of Km:
  • Higher Km means lower affinity.
  • Lower Km means higher affinity.

Graph Analysis

• Vmax Changes:
  • Upward graph shifts indicate increased Vmax (more enzymes).
  • Downward shifts indicate decreased Vmax (fewer enzymes).
• Km Changes:
  • Leftward shifts indicate lower Km (higher affinity).
  • Rightward shifts indicate higher Km (lower affinity).

Applications and Historical Anecdote

• Historical Note: Ancient Egyptians used urine glucose levels as a pregnancy test.
• Clinical Relevance: Understanding enzyme kinetics is critical in drug interaction and metabolic pathways.

Conclusion

• The Michaelis-Menten equation helps understand enzyme kinetics.
• Upcoming Topics:
  • Lineweaver-Burk plot

Resources

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• Offers on courses using promo code 'taxidrome.'

• Note: Understanding enzyme kinetics involves both theoretical knowledge and practical application, especially in medical and biochemical contexts.