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 when epinephrine and glycogen phosphorylase were combined.