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Enzyme Kinetics Examples

Enzyme Kinetics Examples

Three cases will illustrate how this equation behaves.

CASE 1: [S] very large

[S] >> Km. The enzyme is saturated with substrate.

In this case [S] + Km = [S] (approximately), so (5) becomes: or:

This is the rate at large substrate concentration, the maximal rate for [E], which is called Vmax.


Substituting into (5) gives the Michaelis-Menten Equation as it is normally shown:

Remember, this equation is derived for Vo, when very little product has formed and the back-reaction can be ignored.

CASE 2: [S] small

[S] << Km . Then activity is in the linear range.

In this case [S] + Km = Km (approximately) so (5) becomes: or:

So, at low [S], Vo is linearly proportional to [S].

CASE 3: [S]=Km

The definition of Km

Km is defined as the [S] that results in half-maximal rate.

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