enzyme kinetics

What is the basic Michaelis-Menten reaction? [HOMEWORK]

E + S ⇌ ES → E + P.

What is k1?

Rate constant for E + S → ES.

What is k-1?

Rate constant for ES → E + S.

What is k2?

Rate constant for ES → E + P.

Which step does the homework call fast? [HOMEWORK]

Binding step.

Which step does the homework call slow/rate-limiting? [HOMEWORK]

Catalysis step in the simplified example.

What is total enzyme concentration? [HOMEWORK]

[E]Total = [ES] + [E]free.

What is the Michaelis-Menten equation?

v0 = Vmax[S]/(KM+[S]).

What is v0?

Initial reaction velocity.

What is Vmax?

Maximum velocity at substrate saturation.

What is KM?

Substrate concentration at half Vmax in the Michaelis-Menten model.

What is KM in rate constants? [HOMEWORK]

KM = (k-1+k2)/k1.

Why is KM not always equal to binding affinity? [HOMEWORK]

It includes both substrate dissociation and conversion to product.

When does KM approximate Kd? [HOMEWORK]

When k-1 is much greater than k2.

What is Kd? [HOMEWORK]

Dissociation constant = k-1/k1.

What does smaller Kd mean? [HOMEWORK]

Tighter enzyme-substrate binding.

What is Vmax in terms of k2? [HOMEWORK]

Vmax = k2[E]Total.

What is v0 when [S]=KM? [HOMEWORK]

v0 = Vmax/2.

What is v0 when [S]>>KM? [HOMEWORK]

v0 ≈ Vmax.

What is v0 when [S]<<KM? [HOMEWORK]

v0 ≈ (Vmax/KM)[S].

What happens to Vmax if enzyme concentration doubles?

Vmax doubles if other conditions remain constant.

What is the Michaelis-Menten plot X-axis?

[S].

What is the Michaelis-Menten plot Y-axis?

Initial velocity v0.

What is the Michaelis-Menten curve shape?

Hyperbolic.

What is the plateau on Michaelis-Menten curve?

Vmax.

What substrate concentration gives half the plateau?

KM.

What is a Lineweaver-Burk plot?

1/v0 versus 1/[S].

What is the Lineweaver-Burk equation?

1/v0 = (KM/Vmax)(1/[S])+1/Vmax.

What is the Lineweaver-Burk Y-intercept?

1/Vmax.

What is the Lineweaver-Burk X-intercept?

-1/KM.

What is the Lineweaver-Burk slope?

KM/Vmax.

If Y-intercept is 0.02, find Vmax.

50.

If Y-intercept is 0.05, find Vmax.

20.

If X-intercept is -0.25, find KM.

4.

If X-intercept is -0.2, find KM.

5.

If Vmax=100 and [S]=KM, find v0.

50.

If Vmax=120, KM=4, [S]=8, find v0.

80.

If [S]=2KM, what fraction of Vmax is v0?

2/3.

If [S]=3KM, what fraction of Vmax is v0?

3/4.

If [S]=KM/2, what fraction of Vmax is v0?

1/3.

If [S]=4KM, what fraction of Vmax is v0?

4/5.

At very low [S], reaction is what order in substrate?

Approximately first order.

At saturating [S], reaction is what order in substrate?

Approximately zero order.

What happens to velocity as [S] approaches infinity?

Approaches Vmax.

Does doubling [S] always double velocity?

No; velocity approaches saturation.

How can you find KM from a hyperbolic graph?

Read [S] at v0=Vmax/2.

How can you find Vmax from a Lineweaver-Burk graph?

Take reciprocal of Y-intercept.

How can you find KM from a Lineweaver-Burk graph?

Take negative reciprocal of X-intercept.

What is the sign of KM?

Positive even though X-intercept is negative.