Adenylate cyclase (EC 4.6.1.1, also known as adenylyl cyclase, adenyl cyclase or AC) is part of the G protein signaling cascade, which transmits chemical signals from outside the cell across the membrane to the inside of the cell (cytoplasm).

The outside signal binds to a receptor, which transmits a signal to the G protein, which transmits a signal to adenylate cyclase, which transmits a signal by converting adenosine triphosphate to cyclic adenosine monophosphate (cAMP). cAMP is known as a second messenger.

There are ten known adenylate cyclases in mammals:

Adenylate cyclase catalyzes the conversion of ATP to 3',5'-cyclic AMP (cAMP) and pyrophosphate.

cAMP (cyclic adenosine monophosphate) is an important molecule in eukaryotic signal transduction, a so-called second messenger. Adenylate cyclase can be activated or inhibited by G proteins, which are coupled to membrane receptors and thus can respond to hormonal or other stimuli. Following activation of adenylate cyclase, the resulting cAMP acts as a second messenger by interacting with and regulating other proteins such as protein kinase A and cyclic nucleotide-gated ion channels.