Enzyme Kinetics

Question 1

What are the 2 phases of an enzyme catalyzed reaction?

Answer 1

1. Formation of the enzyme substrate complex (E + S) (second order reaction)
2. Turnover step: enzyme substrate complex is converted into product and free enzyme is regenerate (first order reaction)

Question 2

Does phase 1 or phase 2 dominate in an enzyme catalyzed reaction?

Answer 2

• Depends on the substrate concentrations
• Low substrate concentration pushes equilibrium over to the left (dominated by K1)
• High substrate concentration pushes equilibrium over to right (dominated by K2)

Question 3

What two assumptions does the Michaelis-Menton equation require?

Answer 3

1. The reaction is at equilibrium when the velocity of the reaction is measured
2. The reaction is at a steady state ([S]&raquo_space;> [E])

Question 4

What is the Michael’s constant (Km) and what information does it tell you?

Answer 4

• Rate of ES formation
• Measures enzyme-substrate affinity
• Concentration of substrate that gives rise to 1/2 of Vmax
• Modified Kd

Question 5

What does it mean is the Km of a reaction is low?

Answer 5

• Enzyme has high affinity for its substrate
• Small substrate concentration is needed to fill up 1/2 of enzyme active sites

Question 6

What does it mean if the Km of a reaction is high?

Answer 6

• Enzyme has low affinity for its substrate
• High substrate concentration is needed to fill up 1/2 of enzyme active sites

Question 7

What is the Vmax and what information does it tell you?

Answer 7

• The maximum velocity of the reaction
• All of the enzyme is entirely in the enzyme substrate complex

Question 8

Describe the Michaelis-Menton Equation?

Answer 8

Takes into account phase 1 and phase two of the reaction

Question 9

How do you construct a Michaelis-Menton plot?

Answer 9

• Measure the initial velocity of a reaction at different substrate concentrations
• Take these concentration and plot them on the Michaelis-Menton plot

Question 10

Kcat

Answer 10

• Number of catalytic cycles per enzyme per unit time
• Correlates Vmax to how much substrate was added
  Kcat = Km/ET (total enzyme concentration)

Question 11

Catalytic efficiency

Answer 11

Relates turnover rate and affinity for enzyme substrate pair
- Kcat / Km
- Second order