Evidence that the Gh protein is a signal mediator from alpha 1-adrenoceptor to a phospholipase C. I. Identification of alpha 1-adrenoceptor-coupled Gh family and purification of Gh7 from bovine heart.

Our previous studies on alpha 1-adrenoceptor-mediated signaling suggested that Gh is a signal mediator. Gh consists of a 74-kDa GTP-binding alpha-subunit and a 50-kDa beta-subunit. Studies using the alpha 1-agonist-receptor-G-protein ternary complexes from various tissues and species revealed that the intensity (GTP-binding) of the [alpha-32P]GTP-labeled proteins resulting from activating the alpha 1-receptor was significantly attenuated by phentolamine. The molecular masses of GTP-binding proteins were 74 kDa in rat heart and liver, 77 kDa in dog heart, 78 kDa (Gh7 alpha) in bovine heart and liver, and 80 kDa in human heart. Supporting these observations, a specific antibody to Gh7 alpha not only recognized these GTP-binding proteins in the ternary complex preparations, but also co-immunoprecipitated alpha 1-adrenoceptors, indicating a tight association of these GTP-binding proteins with the alpha 1-adrenoceptor. These results also demonstrate that functional and structural similarities exist among these GTP-binding proteins. Additionally, one of the identified G-proteins (termed Gh7) was purified from bovine heart. Gh7 consisted of the 78-kDa GTP-binding protein and a 50-kDa protein.