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.

c. Glycogen breakdown was observed only when epinephrine was administered to intact cells

Explanation:

Earl W Sutherland was an American pharmacologist who the first to isolate cyclic adenosine monophosphate (i.e., cAMP). Later, Sutherland showed that epinephrine induces the formation of cAMP in liver cells, and that this molecule (cAMP) is a second messenger involved in many metabolic processes. In the first time, he discovered that epinephrine triggers the breakdown of glycogen in liver cells by activating glycogen phosphate. However, Sutherland observed that the combined addition of epinephrine, glycogen phosphate enzyme and glycogen in a test tube did not produce the breakdown of glycogen, and thereby suggesting the role of cAMP in this process.