LEC 10: Enzyme Kinetics I

Question 1

What are the 5 Catalytic mechanisms

Answer 1

1. Preferential transition state binding (most enzymes)
2. General acid-base catalysis
3. Covalent catalysis
4. Electrostatic catalysis
5. Metal ion catalyiss

Question 2

What are the characteristics of Preferential transition state binding (2)

Answer 2

1. Enzymes has a higher affinity for the TS than the substrate
2. Promotes reaction

Question 3

What does enzyme kinetics study

Answer 3

The study of enzymatic reaction rates

Question 4

What is Enzyme kinetics base upon

Answer 4

Based upoon determining the rates at which enzymes catalyze reactions and the environemntal factors that influence these rates

Question 5

What do enzyme kinetics allows for a given enzyme (4)

Answer 5

1. Affinity for substrates
2. Efficiency with which they carry out reactions
3. Investigate effectiveness of cofactors and inhibitors
4. Best reaction conditions

Question 6

What variable is represented for reaction rate and what does it mean

Answer 6

V: Moles of product per second (mols/sec)

Question 7

What does V0 indicate

Answer 7

V0: Initial reaction rate

Question 8

What does Vmax indicate

Answer 8

Vmax: Max reaction rate, happens when the enzyme is saturated with the substrate

Question 9

Vmax is affect by ____

Answer 9

Enzyme concentration

Question 10

Vmax is constant per ___ ->___

Answer 10

Enzyme unit -> Kcat

Question 11

What does Kcat indicate

Answer 11

Kcat (turnover rate): # of substrate molecules converted into product per unit of time by a given enzyme, when the enzyme is fully saturated with substarte

Question 12

Kcat of most enzymes fall in the range form __ to __ per second

Answer 12

1 to 10^4

Question 13

What are the characteristics of Km (Michaelis constant) (3)

Answer 13

1. Units: mol/L
2. [S] at which enzyme is half saturated
3. Indicates enzyme affinity for the substrate

Question 14

What does a low Km do

Answer 14

Low [S] needed for half saturation -> High affinity

Question 15

What does a high Km do

Answer 15

High [S] needed for half saturation -> Low affinity

Question 16

What are the 2 forms of the aldehyde dehydrogenase

Answer 16

1. Low Km mitochondrial form (Highly affinity) -> less active in susceptible persons
2. High Km cytoplasmic form (low affinity)

Question 17

What does Kcat/Km do

Answer 17

Indicates how efficient an enzyme is

Useful to compare an enzyme’s preference for different substrates

Question 18

How do you obtain a Michaelis-Menten Curve (7)

Answer 18

1) Measure the concentration of product formed as a function of time for various [S] (and constant [ET]).
2) Plot [P] as a function of time for each [S] (progress curves, not MM curves!)
3) For each [S], determine initial velocity (v0) = slope of the curve at t = 0.
4) Plot v0 vs [S] (this is the Michaelis-Menten curve)
5) Vmax and KM are commonly obtained using curve-fitting computer programs (or use older method: Lineweaver-Burk)
6) Calculate kcat from Vmax and [ET]
7) Calculate specificity constant from kcat and KM