Effect of transmembrane Ca 2+ gradient on G s function

Abstract

G s and adenylate cyclase from bovine brain cortices were co-reconstituted into asolectin liposomes with or without 1000-fold transmembrane Ca 2+ gradient. Obtained results showed that G s activities of both binding GTPγS and stimulating adenylate cyclase were the highest in proteoliposomes, with a transmembrane Ca 2+ gradient similar to the physiological situation and the lowest while the transmembrane Ca 2+ gradient was in the inverse direction. Such a difference could be diminished following the dissipation of the transmembrane Ca 2+ gradient by A23187. Time-resolved fluorescence anisotropy of diphenylhexatriene (DPH) has been used to compare the physical state of phospholipids among those proteoliposomes. It is suggested that a proper transmembrane Ca 2+ gradient is essential for higher membrane fluidity, which may favor G s function with higher GTP-binding activity and stimulation of adenylate cyclase.