disintegrations per minute - radioligand binding (May/12/2008 )

Hi there,

We recently carried out a radioligand binding assay and it says we must graph the DPMs along the y axis with conc. on the x-axis...just wondering what exactly DPMs are..is it the count of how much ligand is bound to the receptor?

bit of a run dwn on the ex:

we used CP55940 with the radioligand SR141716A in and not in the presence of non-hydrolysable analogue, GTPgammaS..what was seen that when the GTPgS was not present, as the concentration of CP55 decrease the CPM increased...(same with in the presence of GTP)...but I guess I am the comparing the DPM at concs. w/ and w/o the GTPgS...
EG. of my results

CONC. DPM;NO GTPgS DPM;WITH GTPgS
1.00E-6M 2653 3184
1.00E-9M 4193 5032

what I am confused about is that when there is GTPgS the SR affinity is increased right? So the more conc. of CPP the more displaced it gets hence the more displaced it gets the DPM should be higher? Does that make annnnnnnnny sense at all or am I just completely wrong?

according to wiki..DPM is the amount of atoms that are decayed/min...tho i still dnt get it..

thx
b_06er

your problem is that you don't know the relationship of dpm to cpm.

cpm is counts per minute detected by the instrument. it can be affected by various factors. the value can be quenched.

dpm is determined by correcting cpm based on the quench factor for the sample. each sample can have a different quench factor so cpm differences between samples may not be as reliable as dpm differences.