Lecture 11: Enzyme kinetics, inhibition and regulation

Question 1

What effect does substrate concentration have on the reaction rate?

Answer 1

As the amount of concentration increases the reaction rate will

• increase in a liner way at first - increase in velocity continues until enzyme becomes saturated with substrate
• BUT as all the active sites become occupied, the rate of reaction stops increasing.

Question 2

What effect does enzyme concentration have on the reaction rate?

Answer 2

As the amount of enzyme is increased, the rate of reaction increases

• VO is proportional to E concentration when S is in excess
• the higher the enzyme conc, the higher the rate of reaction

Question 3

What is first order kinetics?

What is zero order kinetics?

Answer 3

1st order: rate depends on concentration of substrate

0 order: rate does NOT depend on concentration of substrate

Question 4

What is KM - the Michaelis constant?

What is it defined as?

Answer 4

Is the substrate concentration where the reaction is occurring at half the maximum velocity

KM: is defined as the breakdown of ES / the formation of ES

Question 5

Describe the affinities btw E and S for:

low kM?
high KM?

Answer 5

low KM = high affinity btw E and S

high KM = low affinity btw E and S

Question 6

What is k1?

What is k2?

Which one is rate limiting

Answer 6

k1 = how quickly you form an ES complex
E + S ——> ES
k2 = how quickly ES complex is converted to product and released = rate limiting
ES ——-> E + P is RATE LIMITING

Question 7

How is enzyme efficiency measured?

• How is greatest efficiency achieved?
• Hos is least efficiency achieved?

Answer 7

Kcat / KM is a measure of enzyme efficiency
- How quickly product is formed per mole of enzyme per second

Greatest = High Kcat and low KM(high affinity)

Least = Low Kcat and high KM(low affinity)

Question 8

What is Kcat?

How is it calculated?

Answer 8

Kcat = Vmax / (Et)

• Is the turnover number or the catalytic rate constant
• Is the moles of substrate converted to product per mole of enzyme per second
• Units = s-1

Question 9

What is a linear-weaver-burk plot?
What is the slope?
What is the y axis?
What is the x axis?

Answer 9

Is a double reciprocal plot of enzyme kinetics

• slope is Km / Vmax
• the y intercept is 1/Vmax —-> units = min A-1
• The x intercept is -1 / Km —-> units = Lmmol-1