Lecture 8: Michaelis-Menten

Question 1

What are the 4 assumptions you make in the Michaelis Menton equation

Answer 1

1. Catalysis is the rate limiting step, and the Binding step is quick so Kcat < Ka
2. [S]»[E] so enzyme is the limiting factor
3. Steady state: [ES] is constant, meaning rate of formation of [ES]= rate of breakdown
4. The reverse reaction (ES to E + S) is negligible

Question 2

What reaction is the ka, kd and kcat rate constants for

Answer 2

ka is for formation of ES complex from E + S. kd is for breakdown of ES back to E+S. Kcat is for rate of ES to E + Product

Question 3

What is the equilibrium constant for the first reaction (binding) E+S -> ES going forwards vs backwards + units

Answer 3

Going forwards Ka= [ES]/[E][S]= ka/kd. Units: M-1

Going backwards Kd= [E][S]/[ES]= kd/ka Units M

Question 4

What is v (speed of the reaction) =

Answer 4

kcat [ES]

Question 5

What is Vmax (max speed of reaction)=

Answer 5

kcat [E]t (total amount of enzyme)

Question 6

What is Total amount of enzyme [E]t =

Answer 6

[E] + [ES]

Question 7

How is Km (Michaelis constant) derived from the steady state assumption

Answer 7

Steady state assumption says rate of formation of ES = rate of breakdown [ES]. when you translate these rates into k[reactant] then put all the rate constants on one side they make a single constant Km

Question 8

What is the Michaelis-menton equation

Answer 8

v= Vmax [S]/ Km + [S]
Where v = speed of reaction
Vmax= max speed of reaction
Km= Michaelis constant (kd +kcat/ka)
[S] = conc of substrate