Lecture 13 - Enzymes III - Kinetics

Question 1

Which graph is linear for each reaction order type?

L13 S5-7

Answer 1

Zeroth order:
-[S]:time

First order:
-ln[S]:time

Second order:
-1/[S]:time

Question 2

Define K(m), v(max), k(cat), K(s), and k(cat)/K(m).

L13 S15

Answer 2

K(m):

• Michaelis constant
• [S] where reaction rate is half v(max)/half of active sites are full

v(max):
-maximum rate of reaction for a given concentration of enzyme

k(cat):

• turnover number
• number of substrate molecule converted per active site per time (firs order rate constant)

K(s):
-dissociation constant for substrate binding

k(cat)/K(m):

• specificity constant
• measure of enzyme performance predicting fate of E*S

Question 3

What is the Michaelis-Menton equation?

L13 S24

Answer 3

v(0)=v(max)[S]/(K(m)+[S])

Question 4

How does the Michaelis-Menton equation change with the relation of [S] and K(m)?

L13 S25

Answer 4

[S] &laquo_space;K(m):
-v(0) = v(max)[S]/k(m)

[S] = K(m):
-v(0)=v(max)/2

[S]&raquo_space; K(m):
-v(0) =v(max)

Question 5

What is characteristic of a good/poor enzyme with regards to Michaelis-Menton variables?

L13 S26

Answer 5

Judged by specificity constant, K(cat)/K(m)

Good:

• K(cat)&raquo_space; K(-1)
• K(cat)/K(m) = K(1)

Bad:

• K(cat) &laquo_space;K(-1)
• -K(cat)/K(m) = 1/K(m)