Enzyme Kinetics and Structure

Enzyme Kinetics

• Definition: Study of the rates of enzyme-catalyzed reactions.
• Key Concepts:
  • Michaelis-Menten Kinetics: Model explaining the rate of enzyme-catalyzed reactions; characterized by:
    • V₀: Initial reaction velocity.
    • Vmax: Maximum velocity when the enzyme is saturated.
    • Km: Substrate concentration at which the reaction rate is half of Vmax; indicates enzyme affinity for substrate.
  • Turnover Number (kcat): Number of substrate molecules converted to product per enzyme molecule per second.
  • Lineweaver-Burk Plot: Double-reciprocal plot used to determine Km and Vmax.

Enzyme Structure and Function

• Structure:
  • Active Site: Specific region where substrates bind; geometric and chemical complementarity to substrates.
  • Apoenzyme: The protein part of an enzyme without its cofactor.
  • Holoenzyme: Complete enzyme with its cofactor.
• Function:
  • Enzymes lower the activation energy of reactions, increasing reaction rates.
  • Specificity: Enzymes are selective for their substrates, determining the pathway of biochemical reactions.

Enzyme Regulation

• Types of Regulation:
  • Allosteric Regulation: Binding of regulatory molecules at sites other than the active site, causing conformational changes that affect activity.
  • Covalent Modification: Addition or removal of chemical groups (e.g., phosphorylation) alters enzyme activity.
  • Feedback Inhibition: End product of a metabolic pathway inhibits an earlier step to maintain homeostasis.
• Importance: Ensures metabolic pathways are coordinated and responsive to cellular needs.

Catalysis Mechanisms

• Mechanisms:
  • Proximity and Orientation: Enzymes bring substrates into close proximity and correct orientation for reaction.
  • Strain and Distortion: Enzymes induce stress on substrates to facilitate transition states.
  • Acid-Base Catalysis: Enzymes may donate or accept protons to stabilize charged intermediates.
  • Covalent Catalysis: Temporary covalent bonds formed between enzyme and substrate during the reaction.

Enzyme Inhibition

• Types of Inhibition:
  • Competitive Inhibition: Inhibitor competes with substrate for the active site; can be overcome by increasing substrate concentration.
  • Non-competitive Inhibition: Inhibitor binds to an allosteric site; decreases enzyme activity regardless of substrate concentration.
  • Uncompetitive Inhibition: Inhibitor binds only to the enzyme-substrate complex, preventing the reaction from proceeding.
• Reversible vs. Irreversible Inhibition:
  • Reversible: Inhibitor can dissociate from the enzyme.
  • Irreversible: Inhibitor permanently inactivates the enzyme, often by forming covalent bonds.

Enzyme Kinetics

• Enzyme kinetics explores the rates of enzyme-catalyzed reactions.
• Michaelis-Menten Kinetics is a fundamental model characterized by:
  • V₀ represents the initial reaction velocity.
  • Vmax indicates the maximum reaction velocity when the enzyme is fully saturated.
  • Km is the substrate concentration at which the reaction velocity is half of Vmax, reflecting the enzyme's affinity for the substrate.
• Turnover Number (kcat) quantifies substrate conversion to product per enzyme molecule per second.
• The Lineweaver-Burk Plot is utilized for the double-reciprocal analysis to determine Km and Vmax values.

Enzyme Structure and Function

• Active Site is the specific location where substrates bind; it exhibits geometric and chemical complementarity to the substrates.
• Apoenzyme is the inactive protein component of an enzyme, lacking its cofactor.
• Holoenzyme refers to the complete enzyme structure that includes its cofactor.
• Enzymes function by lowering activation energy, which accelerates reaction rates.
• The specificity of enzymes dictates their selective interaction with substrates, influencing biochemical reaction pathways.

Enzyme Regulation

• Types of enzyme regulation include:
  • Allosteric Regulation, where regulatory molecules bind at sites distinct from the active site, inducing conformational changes that influence enzymatic activity.
  • Covalent Modification involves the addition or removal of chemical groups (e.g., phosphorylation) to modify enzyme activity.
  • Feedback Inhibition occurs when the end product of a metabolic pathway inhibits an earlier step, aiding in maintaining metabolic homeostasis.
• Regulation is crucial for coordinating metabolic pathways in response to cellular demands.

Catalysis Mechanisms

• Several mechanisms underpin enzyme catalysis:
  • Proximity and Orientation ensuring substrates are positioned correctly and close enough for effective reaction.
  • Strain and Distortion where enzymes exert stress on substrates, facilitating the formation of transition states.
  • Acid-Base Catalysis involves enzymes donating or accepting protons to stabilize charged intermediates during the reaction.
  • Covalent Catalysis refers to the transient covalent bonds formed between the enzyme and the substrate during the catalytic process.

Enzyme Inhibition

• Enzyme inhibition can manifest in several forms:
  • Competitive Inhibition occurs when an inhibitor competes with the substrate for the active site, where increased substrate concentration can reverse the inhibition.
  • Non-competitive Inhibition happens when an inhibitor binds to an allosteric site, reducing enzyme activity independent of substrate concentration.
  • Uncompetitive Inhibition involves the inhibitor binding only to the enzyme-substrate complex, hindering progression of the reaction.
• Inhibition types are categorized as:
  • Reversible, where the inhibitor can detach from the enzyme.
  • Irreversible, where the inhibitor permanently inactivates the enzyme, often via covalent bond formation.

Explore the essential concepts of enzyme kinetics and structure in this quiz. Understand key models such as Michaelis-Menten and important aspects of enzyme functionality, including active sites and enzyme forms. Test your knowledge of how enzymes catalyze reactions and the significance of kinetic parameters.