Which observation suggested 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.
E) Epinephrine was known to have different effects on different types of cells.

Question

Quizplus · Accepted Answer

The observation that glycogen breakdown was observed only when epinephrine was administered to intact cells suggests that some sort of signal transduction process was involved, which would require a second messenger. If glycogen breakdown occurred in a cell-free extract, this would suggest that the effect was due to a direct interaction between epinephrine and the enzymes involved in glycogen breakdown.

Which Observation Suggested the Involvement of a Second Messenger in Epinephrine's