Chapter 1. 7.1 The Discovery of a Second Messenger

1.1 Section Title

Original Paper

Rall, T. W., E. W. Sutherland, and J. Berthet. 1957. The relationship of epinephrine and glucagon to liver phosphorylase. Journal of Biological Chemistry 224: 463.

Analyze the Data

While studying the action of glycogen phosphorylase, Earl Sutherland and his colleagues determined that this enzyme could be activated by epinephrine only when the entire contents, including membrane fragments, of liver cells were present (see figure). The researchers hypothesized that a cytoplasmic messenger must transmit the message from the epinephrine receptor at the membrane to glycogen phosphorylase, located in the cytoplasm. To test this idea, liver tissue was homogenized and separated into cytoplasmic and membrane components, containing the enzyme and epinephrine receptors, respectively. Epinephrine was added to the membrane fraction and incubated for a period of time. This fraction was then subjected to centrifugation to remove the membranes, leaving only the soluble portion in the supernatant. A small sample of the membrane-free solution was added to the cytoplasmic fraction, which was then assayed for the presence of glycogen phosphorylase activity. The assay showed that active glycogen phosphorylase was indeed present in the cytoplasmic fraction. These results confirmed the hypothesis that a soluble second messenger was produced in response to epinephrine binding to its receptor in the membrane, and then diffused into the cytoplasm to activate the enzyme. Later research by Sutherland identified cAMP as the second messenger involved in the mechanism of action of epinephrine, as well as many other hormones. Sutherland’s research was highly regarded in the scientific community, and in 1971 he won the Nobel Prize in Physiology or Medicine for his discoveries concerning “the mechanisms of the action of hormones.”