Question

1. Assume that you can measure the effects of identical concentration of two inhibitors x and Z, on the K and V M and Vmax of an Enzyme. Which of the following would be consistent with inhibitor X being a more effective inhibitor than Z?

2. Explain why an answer is either wrong/right.

a. Inhibitor X increases KM less than inhibitor Z while neither has an effect on V Max.

b. Inhibitor X decreases KM and VMax two-fold while inhibitor Z decreases both three-fold.

c. Inhibitor X doubles the KM and it decreases VMax by 50% while inhibitor Z triples the KM and it decreases the VMax by 40%.

d. Inhibitor X doubles the KM and it decreases VMax by 50% while inhibitor Z triples the KM and it decreases VMax by 10%.

PLEASE EXPLAIN THOROUGHLY!!!!!!!!!!!!!!!!!

Answer 1

1 / V = Km / (Vmax [S]) + 1 / Vmax … eqn(1)

For a more effective inhibitor, the reaction rate (V) should be minimum.

2

a)

From equation 1

As Km increases, V decreases for the same Vmax. For a more effective inhibitor Km should increase more. Inhibitor Z is more effective.

b)

From equation 1

For the same ratio of Km and Vmax, lower the value of Vmax lower will be the reaction rate V.

Inhibitor Z decreases Vmax three fold. Z is more effective.

c)

Inhibitor X : Km/Vmax = 2/0.5 = 4. Vmax = Vmax * 0.5

Inhibitor Z : Km/Vmax = 3/0.6 = 5. Vmax = Vmax * 0.6

Not much difference between Vmax by inhibitors X & Z.

Greater the ratio of Km/Vmax better the inhibitor.

Inhibitor Z is more effective.

d)

Inhibitor X : Km/Vmax = 2/0.5 = 4. Vmax = Vmax * 0.5

Inhibitor Z : Km/Vmax = 3/0.9 = 3.3. Vmax = Vmax * 0.9

Lower the Vmax better the inhibitor.

Greater the ratio of Km/Vmax better the inhibitor.

Both conditions are satisfied by inhibitor X.

Inhibitor X is more effective.