L24: Enzyme Kinetics 1

• What is the primary focus of enzyme kinetics?

  Examining the rates of enzyme-catalysed reactions
• How do enzymes affect reaction rates?

  They affect reaction rates but not equilibria
• Where does the contact between an enzyme and substrate occur?

  At the active site
• What complex is formed when enzymes bind their substrates?

  An enzyme:substrate (ES) complex
• What do enzymes facilitate in a reaction?

  The formation of transition states and lowering activation barriers
• What is the simple description of an enzyme reaction?

  E + S ⇌ ES ⇌ E + P
• What does the forward rate of formation of the ES complex represent?

  The rate at which the enzyme and substrate combine to form the ES complex
• How does substrate concentration affect the rate of reaction?

  The rate is proportional to the concentration of substrate
• What is the relationship between the rate of reaction and enzyme concentration?

  The rate is proportional to the concentration of enzyme
• How can the relationship between rate, substrate concentration, and enzyme concentration be expressed mathematically?

  V = k$_1$[S][E]
• What does the Michaelis-Menten equation describe?

  The relationship between the rate of enzyme-catalysed reactions and substrate concentration
• What happens to the ES complex in the reaction scheme?

  It can dissociate to E and S or proceed to E and P
• Who were the scientists that generated the Michaelis-Menten equation?

  Leonor Michaelis and Maud Menten
• What reaction did Michaelis and Menten investigate?

  The hydrolysis of sucrose into glucose and fructose
• What factors did Michaelis and Menten conclude affect the initial rate of a reaction?

  The initial substrate concentration, maximum rate, and a constant
• What shape does the plot of the initial rate of an enzyme-catalysed reaction resemble?

  A rectangular hyperbola
• What are the five unknown quantities in the Michaelis-Menten scheme?

  The four rate constants and the concentration of the ES complex
• What happens to the concentration of substrate and product as the reaction proceeds?

  The concentration of S falls while the concentration of P rises
• What was the first step Michaelis and Menten took in their investigation?

  They used a low concentration of E, so [S] >> [E]
• How did Michaelis and Menten determine the initial rate of the reaction?

  By determining the rate of product accumulation at early time points
• What does the slope of the line fitted to early time points represent?

  The initial velocity (rate) of the reaction
• What simplification occurs at early time points in the reaction scheme?

  The reverse reaction can be ignored due to low [P]
• What are the known and unknown parameters when measuring the initial rate?

  Known: [E], [S], [P]; Unknown: [ES], k$_1$, k$_{-1}$, k$_2$
• What did Michaelis and Menten do with their experimental data?

  They calculated initial rates from multiple experiments with varying [S]
• What is the significance of the Michaelis-Menten plot?

  It shows the relationship between initial rate and substrate concentration
• What does the maximum possible rate (V$_{max}$) approach in the Michaelis-Menten plot?


  It approaches asymptotically
• What question did Haldane and Briggs ask regarding the Michaelis-Menten equation?

  Can the Michaelis-Menten equation be derived theoretically?
• What is the steady state argument in enzyme kinetics?

  At steady state, the formation of the ES complex equals its breakdown
• What does the steady state condition imply about the rates of formation and breakdown of the ES complex?

  The rate of ES formation equals the rate of ES breakdown
• What is K$M$ in the context of enzyme kinetics?


  K$M$ is the Michaelis constant, representing substrate concentration at half-maximal reaction rate
• How is the concentration of enzyme related to the Michaelis constant?

  The concentration of E is equal to total enzyme concentration minus the concentration in the ES complex
• What is the first step in rearranging equation 3 in enzyme kinetics?

  Expand the right-hand side
• What does the initial rate of the reaction depend on?

  It depends on the concentration of ES and the rate constant k$_2$
• What is the significance of combining equations 4 and 5 in enzyme kinetics?

  It allows for solving the relationship between the concentration of ES and the initial rate
• What does the Michaelis-Menten equation describe in terms of enzyme activity?

  It describes the maximal rate of reaction when all enzyme active sites are occupied
• What does K$M$ represent when [S] equals K$M$?


  K$M$ is the substrate concentration that gives half-maximal reaction rate
• What is the physiological consequence of low K$M$ in mitochondrial ALDH-2?


  It saturates at low acetaldehyde concentration