Adenylate Cyclase

Adenylyl cyclases (ACs) are enzymes that catalyze the production of cyclic adenosine monophosphate (cAMP) from adenosine triphosphate (ATP). Adenylyl cyclases integrate positive and negative signals that act through G protein-coupled cell-surface receptors with other extracellular stimuli to finely regulate levels of cAMP within the cell. Humans express nine isoforms of membranous ACs and a soluble AC.

Based on regulatory properties, transmembrane ACs are classified into four groups: Group I: Ca²⁺/calmodulin-stimulated AC1, AC3, AC8; Group II: Gβγ-stimulated and Ca²⁺-insensitive AC2, AC4, AC7; Group III: Gαi/Ca²⁺/PKA-inhibited AC5, AC6; Group IV: forskolin/Ca²⁺/Gβγ-insensitive AC9. The soluble AC, unlike the transmembrane ACs, is insensitive to hormones, G proteins and forskolin, a diterpene extracted from the root of the plant Coleus forskohlii that directly activates all isoforms of transmembrane ACs except AC9.