Introduction to Ki (nM) enzyme binding data

[[:]]

I post a bit about receptor binding, which is spoken of in terms of Ki (nM) and what this is may not be clear so this is a link to some basic information:

What does the Ki (inhibition constant) for a drug mean? - Simple and Practical Mental Health

A brief, simple explanation for busy clinicians of what the term "receptor binding affinity" means.

simpleandpractical.com

Here is the basic info:

One commonly used measure of the affinity (strength) with which a drug binds to a particular type (or subtype) of receptor is its Ki or inhibitory constant (also called the inhibition constant).

In plain English, the Ki represents the concentration of the drug (in nanomoles or nM) required to occupy 50% of those receptors. For example, the Ki of a particular antipsychotic at postsynaptic D2 receptors is the concentration of that drug that would result in the drug occupying 50% of those receptors.

We need to remember the following, which is obvious from the above:

The LOWER the Ki for a particular drug at a particular receptor, the STRONGER its binding affinity for that receptor.

This is because the lower Ki means that the drug can occupy 50% of those receptors even when the drug is present in a lower concentration.

This information can help readers understand Ki binding data for psychedelic molecules, which is information that is shared in certain types of scientific papers.

 

[[:]]

From another site:

• The inhibitory constant (Ki) and the IC50 of a drug that is known to cause inhibition of a cytochrome P450 (CYP) enzyme have to do with the concentration needed to reduce the activity of that enzyme by half. More specifically the Ki is reflective of the binding affinity and the IC50 is more reflective of the functional strength of the inhibitor for a drug. Since the Ki takes into account the IC50 is its calculation, the Ki is being reported more often by drug companies.
• For noncompetitive inhibition of enzymes, the Ki of a drug is essentially the same numerical value as the IC50, whereas for competitive and uncompetitive inhibition the Ki is about one-half that of the IC50's numerical value.
• The smaller the Ki, the greater the binding affinity and the smaller amount of medication needed in order to inhibit the activity of that enzyme. If a Ki is much larger than the maximal drug concentrations that a patient is typically exposed to from typical dosing, then that drug is not likely to inhibit the activity of that enzyme.