57. Epinephrine signaling, which stimulates glycogen breakdown in liver cells, relies on a G protein- coupled receptor (GPCR) pathway. If a mutation renders the G protein’s ? -subunit unable to hydrolyze GTP to GDP, how will the cellular response be affected? (A) The signaling pathway will fail to initiate. (B) Adenylyl cyclase will remain permanently inhibited. (C) Glycogen breakdown will occur continuously. (D) The receptor will become desensitized to epinephrine immediately. (E) The cell will require higher concentrations of epinephrine to initiate a response.