wwd 7.1 discovery of a second messenger
TRANSCRIPT
7/27/2019 WwD 7.1 Discovery of a Second Messenger
http://slidepdf.com/reader/full/wwd-71-discovery-of-a-second-messenger 1/2
Life: The Science of B iology , Tenth Edition
Sadava • Hillis • Heller • Berenbaum
Working with Data 7.1: The Discovery of a Second Messenger
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.http://www.jbc.org/cgi/reprint/224/1/463
Analyze the Data
While studying the action of glycogen phosphorylase, Earl Sutherland and his colleaguesdetermined that this enzyme could be activated by
epinephrine only when the entire contents,including membrane fragments, of liver cells were
present (see textbook Figure 7.11). The researchershypothesized that a cytoplasmic messenger musttransmit 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 intocytoplasmic 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 tocentrifugation to remove the membranes, leaving
only the soluble portion in the supernatant. A smallsample of the membrane-free solution was added
to the cytoplasmic fraction, which was thenassayed for the presence of glycogen
phosphorylase activity. The assay showed that
active glycogen phosphorylase was indeed presentin the cytoplasmic fraction. These resultsconfirmed the hypothesis that a soluble secondmessenger was produced in response toepinephrine binding to its receptor in the
membrane, and then diffused into the cytoplasm toactivate the enzyme. Later research by Sutherland
identified cAMP as the second messenger involvedin the mechanism of action of epinephrine, as well
as many other hormones. Sutherland’s researchwas 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.”
7/27/2019 WwD 7.1 Discovery of a Second Messenger
http://slidepdf.com/reader/full/wwd-71-discovery-of-a-second-messenger 2/2
Question 1
As part of Sutherland’s research, the activity of glycogen phosphorylase was measured in va rious liver cell fractions, with or without incubation with epinephrine. The table shows the results. Explain how
these data support the hypothesis that there is a soluble second messenger that activates the enzyme.
Question 2
Propose an experiment to test whether the factor (second messenger) that activates the enzyme is stable
on heating (and therefore probably not a protein), and give predicted data.
Question 3
The second messenger, cAMP, was purified from the hormone-treated membrane fraction. Propose
experiments to show that cAMP could replace the membrane fraction and hormone treatment in theactivation of glycogen phosphorylase, and create a table to show possible results.
Condition Enzyme activity (units)
Homogenate 0.4
Homogenate + epinephrine 2.5
Cytoplasm 0.2
Cytoplasm + epinephrine 0.4
Membranes + epinephrine 0.4
Cytoplasm + membranes +
epinephrine2.0