Enzyme Activity and Regulation Study Notes

Learning Objectives

  • Assign an enzyme to the correct class based on its reaction.
  • Describe changes in enzyme activity with varying substrate concentration, enzyme concentration, temperature, or pH.
  • Define and identify reversible and irreversible inhibition.
  • Define and identify uncompetitive and competitive inhibition.
  • Define and identify allosteric control.
  • Define feedback control and explain its role in regulating enzyme catalysis.

Key Factors Affecting Enzyme Activity

  • Substrate Concentration:

    • An increase in substrate concentration increases the reaction rate at constant enzyme concentration until saturation is reached.

  • Enzyme Concentration:

    • Increasing enzyme concentration raises the reaction rate (at constant substrate concentration), as more substrate can bind to available enzymes.

  • Temperature:

    • Enzymes typically have an optimum temperature (often 37 °C in humans).
    • Lower temperatures yield little activity, whereas high temperatures may denature enzymes, reducing activity.

  • pH Levels:

    • Each enzyme has an optimum pH (near 7.4 in the body).
    • Extreme pH can disrupt enzyme tertiary structure, leading to loss of activity.

Regulation of Enzyme Activity

  • Activators and Inhibitors:
    • Activator: Increases enzyme activity by binding to it.
    • Inhibitor: Decreases or destroys enzyme activity.
    • Reversible Inhibition: Inhibitors detach from enzymes.
    • Irreversible Inhibition: Inhibitors attach covalently, preventing substrate binding.

Types of Inhibition

  • Competitive Inhibitors:

    • Similar in structure to the substrate, compete for the active site.
    • Their effect can be reversed by increasing substrate concentration.

  • Noncompetitive Inhibitors:

    • Have distinct structures from substrates, altering enzyme shape and preventing substrate binding.
    • Cannot be alleviated by adding more substrate.

Allosteric Control

  • Allosteric enzymes have effector molecules bind at an alternative site (not the active site).
    • Negative Allosterism: Slows enzyme action.
    • Positive Allosterism: Speeds up enzyme action.

Feedback Control

  • A product of a reaction acts as a regulator, binding to the first enzyme in a pathway (E1) to inhibit further reaction when sufficient product is present.

Protein Modification

  • Enzyme activity can be regulated through covalent modifications, such as phosphorylation (adding/removing phosphate groups).
    • Modification often involves serine, threonine, or tyrosine residues.

Vitamins and Minerals

  • Water-Soluble Vitamins:

    • Contain polar groups, leading to solubility in aqueous environments.
    • Primarily function as coenzyme components (e.g., B-vitamins, vitamin C).

  • Fat-Soluble Vitamins:

    • Stored in body fat, with known deficiency effects but less understood mechanisms.
    • Vitamins A, D, E, and K each play important roles in various biological functions.

  • Antioxidants:

    • Substances that prevent oxidation; dietary examples include vitamins C, E, and selenium.

  • Essential Minerals:

    • Micronutrients vital for enzyme functions; deficiencies can lead to health issues.
Summary of Enzyme Activity and Regulation:
  • Enzymes are sensitive to environmental factors (concentration, temperature, pH).
  • Regulation includes inhibition (reversible and irreversible), allosteric interactions, feedback control, and protein modification.
  • Nutritional components (vitamins and minerals) are crucial for enzymatic functions and overall health.