Question

If the Km of the substrate is equal to the dissociation constant of the substrate Kd, and Ki is greater than Km, which binds more tightly, the inhibitor or the substrate?

I have done an experiment and found that Km = 2.15x10-4 M and Ki = 3.92x10-4 M

How do you know if the inhibitor or substrate binds more easily?

also what does this imply for the recognition of the substrate by the protein?

Answer 1

K values like these are (falls apart)/(forms) expressions. See below

Explanation:

In general, `K_m = ("ES complex falling apart")/("ES complex forming")`

So a larger K value means the binding is less tight. A small value for Km means the binding (or affinity for the substrate) is higher (tighter).

Since your Km is smaller than Ki, this implies the substrate binds more tightly to the enzyme active site than does the inhibitor.

The binding event is dynamic, and so is constantly on/off...so this means that the substrate will occupy the active site more than the inhibitor (just based on K values...not relating to concentrations). But the inhibitor will also occupy the active site significantly (since their K values aren't that much different).