Adenylate cyclase (EC 4.6.1.1, also known as adenylyl cyclase, adenyl cyclase or AC) is an enzyme with key regulatory roles in nearly all cells. It is the most polyphyletic known enzyme: six distinct classes have been described, all catalyzing the same reaction but representing unrelated gene families with no known sequence or structural homology. The best known AC class is class III or AC-III (Roman numerals are used for classes). AC-III occurs widely in eukaryotes and has important roles in many human tissues (see below).
All classes of AC catalyze the conversion of ATP to 3',5'-cyclic AMP (cAMP) and pyrophosphate. Divalent cations (usually Mg) are generally required and appear to be closely involved in the enzymatic mechanism. The cAMP produced by AC then serves as a regulatory signal via specific cAMP-binding proteins, either transcription factors or other enzymes (e.g., cAMP-dependent kinases).
Read more about Adenylate Cyclase: Class I AC, Class II AC, Class III AC, Class IV, Class V and IV, Additional Images