adenylate cyclases

Adenylyl (adenylate) cyclases are enzymes, which cross the membrane twelve times (right) and which convert ATP to the second-messenger cAMP (3',5' cyclic AMP) and pyrophosphate (below left). Likewise, guanylate cyclases convert GTP to the second messenger, cGMP. Adenylyl cyclases are coincidence detectors, meaning that they are only activated by several different signals occurring together – they are modulated by G-proteins, forskolin, Ca2+/calmodulin, and other class-specific substrates.