Question of Kd

Anders Fugelli anders.fugelli at
Tue Nov 21 08:20:12 EST 1995

In article <48qtcj$2jb at>, Thomas W Bluem
<tbluem at> wrote:

> Help ... Help ... Help ... Help ...
> What does this mean:
>   K  = 1 mM  ???
>    D
> What is K   ?
>          D
> Thanks in advance.
> T. W. Bluem, Dept. of Anatomy and Cellbiology, University of Heidelberg, 
> Germany

The definition of this, can be found in most textbooks of pharmacology
(under Hill equation),
but in brief it relates to the dissociation constant of an Agent, A to its
It is often refered to as the [A]50, which simply relates to the
concentration at which there
is a 50% effect.  This latter is most appropriatly used in indirect
measurements, whereas Kd is
measured in more direct ways, such as by radioligand binding experiments.
For a quick reference, see; Jenkinson, D.H. et al, Pharmacological Reviews
47: 255-266

In your case, Kd=1 mM, means that at a concentration of 1 mM, half your
receptors will be occupied 
(A fairly high Kd value in terms of affinity)

Anders Fugelli
anders.fugelli at
Institute of Neurophysiology
University of Oslo

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