Title : Discrepancies in the specific activity of 3H-N-methylscopolamine as determined by mass spectrometry and radioreceptor assay due to racemisation - Ensing_1988_J.Recept.Res_8_871 |
Author(s) : Ensing K , Bloemhof DA , in 't Hout WG , de Zeeuw RA |
Ref : J Recept Res , 8 :871 , 1988 |
Abstract :
In radioligand binding studies, the accuracy of the specific activity of the radiolabeled ligand has a large impact on the calculated receptor concentration and on the calculated affinities of both labeled and competitive ligands. A radioreceptor assay for anticholinergic drugs was employed to determine the specific activity of 3H-N-methylscopolamine in which the assumption was made that the labeling does not affect the interaction between the ligand and the muscarinic receptor. With this method a specific activity of 48 Ci/mmole was determined which was about 60% of the manufacturer's specification. However, the specific activity as determined by mass-spectrometry with field desorption showed 2.8 tritium-atoms per molecule NMS corresponding with an specific activity of 84.5 Ci/mmole. The only explanation for this discrepancy was a racemisation of the label, which could be proven by titration of the label with an increasing receptor concentration showing that 40% was not bound at all. This was attributed to the formation of the (+)-isomer. |
PubMedSearch : Ensing_1988_J.Recept.Res_8_871 |
PubMedID: 3193405 |
Ensing K, Bloemhof DA, in 't Hout WG, de Zeeuw RA (1988)
Discrepancies in the specific activity of 3H-N-methylscopolamine as determined by mass spectrometry and radioreceptor assay due to racemisation
J Recept Res
8 :871
Ensing K, Bloemhof DA, in 't Hout WG, de Zeeuw RA (1988)
J Recept Res
8 :871