Enzymes and Enzyme Kinetics

Enzymes

  • Definition: Protein catalysts that accelerate reaction rates; usually have "-ase" suffix.
  • Example: Lactase breaks down lactose into glucose and galactose.

Classes of Enzymes

  1. Oxidoreductases: Catalyze oxidation-reduction reactions.
  2. Transferases: Transfer functional groups (e.g., methyl, phosphate).
  3. Hydrolases: Cleave bonds by hydrolysis (addition of water).
  4. Lyases: Break bonds without hydrolysis/oxidation.
  5. Isomerases: Rearrange atoms within a molecule.
  6. Ligases: Join molecules using ATP for energy.
  7. Translocases: Move ions/molecules across membranes.

Enzyme Characteristics

  • Not consumed in reactions; can be reused.
  • Bind specific substrates at active sites.
  • May require coenzymes (vitamins) or cofactors (minerals).
  • Allosteric regulation can occur (non-active site binding).

Enzyme Action

  • Formation of enzyme-substrate (ES) complex lowers activation energy.
  • Equilibrium between reactants/products is unchanged.
  • Factors affecting kinetics:
    • Substrate concentration: Increased concentration raises velocity until saturation (Vmax).
    • Temperature: Higher temp increases velocity until denaturation.
    • pH: Each enzyme has an optimal pH for activity.

Michaelis-Menten Kinetics

  • Equation: V0 = \frac{V{max}[S]}{K_m + [S]}
  • Vmax: Maximum reaction velocity at saturation.
  • Km: Substrate concentration at half Vmax; indicates enzyme affinity.
  • Graphs: Shows hyperbolic relationship of [S] vs. V0.

Inhibition Types

  • Competitive Inhibition: Inhibitor competes for active site; increases Km without changing Vmax.
  • Non-competitive Inhibition: Inhibitor binds allosterically; decreases Vmax without changing Km.

Regulation of Enzyme Activity

  • Allosteric Regulation: Binding affects activity positively or negatively.
  • Covalent Regulation: Modification via phosphorylation/dephosphorylation.
  • Feedback Inhibition: Regulatory mechanism in metabolic pathways.

Clinical Relevance

  • Enzyme levels can indicate tissue damage or disease when altered.
  • Blood plasma protein measurements are common in diagnostics.

Summary Points

  • Enzymes increase reaction rates without altering equilibrium.
  • Kinetics influenced by substrate conditions, temperature, and inhibitors.
  • Various inhibition modes and regulatory mechanisms modulate enzyme function.