What secondary messenger is formed from ATP in the GPCR signaling pathway?

In the GPCR (G-protein coupled receptor) signaling pathway, the formation of cAMP (cyclic adenosine monophosphate) from ATP is a critical step in transmitting the signal from the receptor to other parts of the cell. When a ligand binds to a GPCR, it activates the associated G-protein, causing a conformational change that allows it to exchange GDP for GTP. The activated G-protein can then stimulate adenylyl cyclase, an enzyme that converts ATP into cAMP.

cAMP acts as a secondary messenger that amplifies the signal within the cell and is involved in activating protein kinase A (PKA). This activation leads to a cascade of further reactions that ultimately result in various physiological responses, such as changes in gene expression, enzyme activity, or ion channel conductance.

In summary, cAMP is the key secondary messenger produced from ATP in the GPCR signaling pathway, making it essential for the transmission of signals initiated by hormone binding and other extracellular stimuli.