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.

Question

Quizplus · Accepted Answer

Glycogen breakdown occurring only when epinephrine was administered to intact cells suggested to Sutherland the involvement of a second messenger, as the direct interaction between epinephrine and the enzymes inside the cells could not explain the observed effects. This indicated that epinephrine's effect was mediated through an internal cellular process initiated by its binding to cell surface receptors.

Which Observation Suggested to Sutherland the Involvement of a Second