Which Observation Suggested to Sutherland the Involvement of a Second

Multiple Choice

Which observation suggested to Sutherland the involvement of a second messenger in epinephrine's effect on liver cells?

A) Enzymatic activity was proportional to the amount of calcium added to a cell-free extract.
B) Receptor studies indicated that epinephrine was a ligand.
C) Glycogen breakdown was observed only when epinephrine was administered to intact cells.
D) Glycogen breakdown was observed only when epinephrine and glycogen phosphorylase were mixed.