“…The efficacy of Phd binding to G␥ is determined, in part, by its phosphorylation state at serine 73 (29). The balance between phosphorylation by cyclic AMP-dependent protein kinase A and dephosphorylation by protein phosphatase 2A results in an increase of phosphorylated Phd during darkness and its decrease upon exposure to light (4,9,25,26,29,63,65). The dephosphorylated form of Phd favors the binding of G␥, which, in light, prevents receptor-mediated G␣ reactivation (32,65) and blocks interactions between G␥ and its effectors (25,26,41,64).…”