2.3 Enzyme Kinetics [HY]

Question 1

What is factor affecting enzyme kinetics?

Answer 1

• environmental conditions
• concentrations of substrate and enzyme

Question 2

What does adding more substrate do?

Answer 2

• the rate of the reaction will increase
• as we add more and more, begin to level off and reach a maximal rate of relaxation

Question 3

Saturation

Answer 3

• It cannot go any faster once it has reached this point
• the enzyme is working at maximum velocity, denoted by vmax.
• The only way to increase vmax is by increasing the enzyme concentration. Adding more substrate will not increase the rate of reaction.

Question 4

Velocity of the enzyme, Michaelis–Menten equation

Answer 4

v = vmax [S] / Km + [S]

Question 5

Km

Answer 5

• the substrate concentration at which half of the enzyme’s active sites are full
• intrinsic property
• When the reaction rate is equal to half of vmax, Km = [S]
• Michaelis constant, used to compare enzymes

Question 6

What do low Km and high Km denote?

Answer 6

• A low Km reflects a high affinity for the substrate
• a high Km reflects a low affinity of the enzyme for the substrate

Question 7

Relationship between [S] and Km

Answer 7

• When [S] < Km then change in [S] changes rxn rate
• When [S] > Km then change in [S] doesn’t have much affect

Question 8

Kcat

Answer 8

• # substrate converted to product

Question 9

Vmax

Answer 9

• vmax = [E] Kcat
• represents maximum enzyme velocity
• measured in moles of enzyme per second

Question 10

What’s considered catalytically efficient?

Answer 10

• Large Kcat, Low Km
• Basically lots of product, and high enzyme affinity

Question 11

Lineweaver–Burk Plots

Answer 11

• Actual data is on the right but the left is included to show the x intercept.
• The intercept of the line
  with the x-axis gives the value of − 1/Km
• The intercept of the line with the y-axis
  gives the value of 1/vmax
• useful when determining the type of inhibition that an enzyme is experiencing

Question 12

Cooperative enzymes

Answer 12

• show sigmoidal (S-shaped) owing to cooperativity among substrate binding sites
• have multiple subunits and multiple active sites
• often regulatory enzymes in
  pathways
• subject to activation and inhibition, both competitively and through allosteric sites

Question 13

Subunits and enzymes states

Answer 13

• a low-affinity tense state (T) or a high-affinity relaxed state (R)
• Binding of the substrate
  encourages the transition of other subunits from the T state to the R state.
• Increase substrate binding leads to R, and decrease in substrate binding leads to T

Question 14

Hill’s coefficient

Answer 14

• Quantifies cooperativity
• The value of Hill’s coefficient indicates the nature of binding by the molecule
• Hc >1 = high affinity after 1st ligand binds
• Hc <1 = low affinity after 1st ligand binds
• Hc = 1 then enzyme doesn’t cooperatively bind