W26 L3 - Enzyme Kinetics and Michaelis-Menten Equation

Flashcards reviewing key concepts from a lecture on enzyme kinetics, focusing on the Michaelis-Menten equation, Km, Vmax, and their relationships.

What is the Michaelis-Menten equation?

v = Vmax * [S] / (Km + [S])

where v is the reaction rate, Vmax is the maximum rate, [S] is the substrate concentration, and Km is the Michaelis constant.

What does Vmax represent in the Michaelis-Menten equation?

Vmax tells us how the enzyme behaves when the substrate concentration is very high, approaching infinity.

It represents the maximum rate of reaction when the enzyme is fully saturated with substrate.

What does Km represent in the Michaelis-Menten equation?

Km (Michaelis constant) represents the substrate concentration at which the reaction rate is half of Vmax.

It indicates the affinity of the enzyme for the substrate; a low Km means high affinity, and a high Km means low affinity.

How is Km related to the rate constants in the enzyme-substrate reaction scheme?

Km is defined as (k-1 + kcat) / k1,

where k1 is the rate constant for the formation of the enzyme-substrate complex,

k-1 is the rate constant for the dissociation of the ES complex back into free enzyme and substrate

kcat is the rate constant for the formation of product.

Does Km depend on the enzyme concentration?

No, Km does not depend on the enzyme concentration because it is made up of constants. It is a constant that reflects the affinity of the enzyme for its substrate.

What is enzyme saturation?

Enzyme saturation refers to the extent to which the enzyme's active sites are occupied by the substrate. 100% saturation means all enzyme molecules have substrate bound.

How is Vmax related to the total enzyme concentration?

Vmax = kcat * [E]_total,

where [E]_total is the total enzyme concentration.

Thus, Vmax is directly proportional to the enzyme concentration.

If the enzyme concentration is doubled, what happens to Vmax?

If the enzyme concentration is doubled, Vmax also doubles because Vmax = kcat * [E]_total.

If the enzyme concentration is doubled, what happens to Km?

Km remains the same because it does not depend on the enzyme concentration.

It only depends on the rate constants: Km = (k-1 + kcat) / k1.

How do Vmax and Vmax/Km depend on the enzyme concentration?

Both Vmax and Vmax/Km depend on the enzyme concentration.

If the enzyme concentration increases, Vmax and Vmax/Km will increase proportionally.

How to calculate the substrate concentration needed to achieve a certain saturation percentage?

By setting v = (desired saturation percentage) * Vmax in the Michaelis-Menten equation and solving for [S].

p being the desired saturation percentage (as a decimal e.g 0.9)

What is the substrate concentration at 50% saturation?

The substrate concentration at 50% saturation is equal to Km. This is because Km is defined as the substrate concentration at which the reaction rate is half of Vmax.