[35S]GTPgammaS binding studies of amphiphilic drugs-activated Gi proteins: A caveat

This paper documents a serious problem met during the testing of Gi protein-activating properties of a new series of synthetic compounds by measuring the induced binding of [35S]GTPgammaS to different subtypes of Gi protein. The problem arose from the strong affinity between [35S]GTPgammaS and the tested compounds, that are characterized by several (2–4) positive charges and high lipophilicity. Apparently, such affinity yields insoluble, labelled complexes that, also in the absence of Gi protein, are retained on the filters and give rise to false positive results.