And what that means is it binds guanial nucleotides such as GDP and GTP. Now, before the epinephrine actually binds, the alpha domain contains a GDP, a guanosine diphosphate. And when the guanosine diphostate is bound to that alpha domain, the alpha domain has a very high affinity for the seven TM domain and these other two domains. And that's why we have this structure shown here. The alpha domain is bound to these two domains as well as to that seven TM domain. So when epernphrine is not bound to the beta adrenergic receptor beta arm, the g protein binds guanosine diphosphate, GDP, and this keeps that trimeric domain intact and attached onto that seven TM domain, as we see in this diagram.