Enzyme, Pharmaceutical Aids, Miscellaneous Last Part of Chapter no 5th.pdf
Cyclic AMP and Calcium Ions as Second Messengers
1.
2. They were discovered by Earl Sutherland and Ted Rall as heat
stable factor that mediated the intracellular actions of the
hormones glucagon and epinephrine on glycogen metabolism
in the liver
That factor was- cyclic AMP, a discovery that earned
Sutherland a Nobel Prize in 1971
The next signaling molecule to be officially considered as a
second messenger was the calcium ion by pioneering work of
London-based physiologist Sydney Ringer. The acceptance of
the general signal transduction function of Ca2+, as originally
proposed by Lewis Victor Heilbrunn
3.
4.
5.
6.
7. Second messengers fall into four major classes:
1. cyclic nucleotides, such as cAMP and other
soluble molecules that signal within the cytosol;
2. lipid messengers that signal within cell
membranes;
3. ions that signal within and between cellular
compartments; and
4. gases and free radicals that can signal
throughout the cell and even to neighboring cells.
8. They are also known as intracellular messengers,
share common properties :
1. They can be synthesized/released and broken down
again in specific reactions by enzymes or ion
channels.
2. Some (such as Ca2+) can be stored in
special organelles and quickly released when
needed.
3. Their production/release and destruction can
be localized, enabling the cell to limit space and
time of signal activity.
9. Second messengers are small molecules can be synthesized
and destroyed quickly.
They can be made readily
Act at high and low concentrations of target proteins
Low affinity permits rapid dissociation.
They also can diffuse quickly within the cell, although many
cells have developed mechanisms to spatially restrict such
diffusion.
Second messengers are, thus, superior to proteins in
mediating fast responses, particularly at a distance
They can be addressed to large numbers of target proteins
simultaneously.
These advantages often overcome their lack of catalytic
activity and their inability to bind multiple molecules
simultaneously
