The membrane bound adenylyl cyclases (ACs) represent one of the major families of effector enzymes for G protein coupled receptors. Eight human AC isoforms (AC-1 through AC-4) have been identified up to now and genes for at least nine adenylate cyclase (AC-1-AC-9) have been cloned characterized and sequenced. This is a calmodulin-sensitive adenylyl cyclase which may be involved in regulatory processes in the central nervous system. It may play a role in neuronal plasticity, memory acquisition and learning and is expressed predominantly in the brain, retina and adrenal medulla.