Signal Amplification and Termination in Cell Signaling
This article discusses the two main mechanisms by which cell signaling is amplified and terminated:
- Amplification: The binding of a single ligand to a receptor can stimulate a large number of adenylyl cyclases, which produce a large number of cAMP molecules. Each two cAMP molecules activate a protein kinase A (PKA), which in turn phosphorylates a number of other proteins. This process can amplify the signal manyfold.
- Termination: The signal is terminated by phosphatase-1, which removes phosphate groups from the different enzymes involved in the signaling pathway. The activity of phosphatase-1 is regulated by inhibitor-1, which is itself activated by PKA. When the hormone dissociates from its receptor and adenylyl cyclase is shut down, cAMP levels quickly drop. This inactivates PKA and thus inhibitor-1, leading to the activation of phosphatase-1.
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