Which of the following observations suggests that a second messenger is required for the activation of glycogen phosphorylase by epinephrine?
A) Glycogen phosphorylase is inactive in the absence of epinephrine in a cell-free system.
B) Glycogen breakdown occurs only when epinephrine is administered to intact cells.
C) Glycogen breakdown occurs when epinephrine and glycogen phosphorylase are combined in a cell-free system.
D) Epinephrine binds directly to glycogen phosphorylase.

Question

Quizplus · Accepted Answer

Glycogen breakdown occurring only when epinephrine is administered to intact cells suggests the involvement of a second messenger. This is because the direct effects of epinephrine (a hormone) on enzymes like glycogen phosphorylase typically require a signaling cascade within the cell, which often involves second messengers to relay the signal from the cell surface to the target enzyme.

Which of the Following Observations Suggests That a Second Messenger