Kinetics Overflow

Question 2

E + S ⇌ ES ⇌ E + P

what is k₁?

Answer 2

equilibrium constant for forming enzyme-substrate from E and S.

k₁ = [ES]/[E][S]

Question 3

E + S ⇌ ES ⇌ E + P

what is k₂?

Answer 3

equilibrium constant for forming enzyme + product from ES.

k₂ = [E][P]/[ES]

Question 4

E + S ⇌ ES ⇌ E + P

how to calculate Rate₁?

Answer 4

Rate₁ = k₁ [E][S]

(rate constant k₁ = [ES]/[E][S]), assumed to be

Question 5

E + S ⇌ ES ⇌ E + P

how to calculate Rate₂?

Answer 5

Rate₂ = k₂ [ES]

( rate constant k₂ = k_cat = V_max/[E]_t )

Question 6

steady-state assumption in enzyme kinematics

Answer 6

E + S ⇌ ES ⇌ E + P

steady-state assumption: [ES] is constant

formation of ES = loss of ES

Rate₁ + Rate_-2 = Rate_-1 + Rate₂

Rate_-2 is generally ignored because we assume that formation of E + P is thermodynamically favourable and so that the reverse reaction is negligible, so

E + S ⇌ ES ⟶ E + P

Rate₁ = Rate_-1 + Rate₂

Question 7

E + S ⇌ ES ⇌ E + P

what is the rate of formation of ES?

Answer 7

Rate₁ + Rate_-2

both of these reactions lead to formation of ES, either from forward reaction of E+S ⟶ ES (Rate₁) or reverse reaction of ES ⟵ E+P (Rate_-2)

Question 8

E + S ⇌ ES ⇌ E + P

Why do we generally ignore Rate_-2?

( E + S ⇌ ES ⟶ E + P )

Answer 8

We assume

Question 9

E + S ⇌ ES ⇌ E + P

how to calculate Rate_-1?

Answer 9

Rate_-1 = K_-1 [ES]

(rate constant K_-1 = [E][S]/[ES])