FIGURE 7.

Schematic model of the G protein cycle. Active receptors interact with heterotrimeric GDP- or GTP-bound G proteins, as investigated in this study and indicated in red in the model. Upon interaction, nucleotide is released. Subsequently, complexes of nucleotide-free G proteins and active receptors are transiently formed. Upon binding GTP, G proteins become active, facilitating dissociation from active receptors. Both GDP- and GTP-bound G proteins are in equilibrium between heterotrimeric conformation and dissociation of subunits. G_GTP, G_GDP, and G indicate GTP-bound, GDP-bound, or nucleotide-free G proteins, respectively; R*, indicates active receptors.