The cAMP synthesizing enzymes are found in two forms: cytosolic (soluble) and membrane-bound (particulate). Stimulation of adenylate cyclases produce cAMP form ATP in response to the activation of GPCRs by various hormones, neurotransmitters and other regulatory molecules. cAMP, in subsequent steps down the signal transduction pathway, can stimulate cAMP-dependent protein kinase A (cPKA), and several other target molecules. Activation of cPKA can phosphorylate a broad range of substrates that regulate various metabolic pathways, gene expression, and affect memory functions etc. The stimulation of adenylate cyclases starts with interactions with GPCRs mediated signals initiated by Gs and Gi heterotrimeric G-proteins.