Table 1.

The two distinct classes of mammalian adenylyl cyclase.

	sAC	tmACs
Evolutionary relatedness	(Cyano)bacteria	‘First’ Appearance: Dictyostelium
Isoform variability	One gene with multiple splice variants and an alternative start site	Nine distinct genes
Tissue distribution	Ubiquitous	Ubiquitous
Subcellular localization	Cytoplasm, nucleus, mitochondria, centrioles, mitotic spindle, mid-body	Plasma membrane
Physiological Modulators	Bicarbonate, calcium, & ATP	G proteins & other 2nd messengers
Functions	HCO3− sensing in sperm pH sensing in acid/base sensing epithelia CO2 sensing in airway cilia and mitochondria	Intercellular signaling (i.e., hormones, neurotransmitters, odorants)