Biochemistry & Analytical Biochemistry

Abstract

Heparin Clearance by Liver Scavenger Receptors

Edward N. Harris

The range of assay technologies for the binding and signaling has been developed in HTS laboratories for the identification of hit or lead compounds acting on GPCRs. The [35S] GTPγS binding assay still remains to be a useful and simple technique to demonstrate receptor activation and is one of the few functional, cell-free assays. However, its radioactive nature imposes clear limitations to its use in regular laboratory practice and in high-throughput experimentations. Herein, we have developed a new non-radioactive version of the assay using europium-labeled GTP analogue in which europium-GTP binding can be assayed using time-resolved fluorescence. In continuation with our efforts, this assay was adapted for Histamine 3 receptors. The assay format was specifically evaluated by testing known histamine 3 agonists (Imetit, Immepip, Methylhistamine, Proxifan and Histamine) and antagonists (GSK189254, Clobenpropit and Thioperamide) drugs. Under optimized assay conditions, the potencies (pEC50 & PKB) in the binding assay are in good agreement with those obtained previously in the isotopic functional activity assay. The Eu-GTP binding assay was observed to be highly robust (Z’ factor 0.84) with high percentage over basal counts. This assay can be utilized as a component of screening cascade for the screening of Histamine 3 receptor antagonists.