Structural and regulatory properties of nucleotide binding regulatory N proteins of adenylate cyclase and their effects on hormone receptors

The adenylate cyclase (AC) system is responsible for the synthesis of the second messenger cAMP which mediates the effects of many hormones and neurotransmitters on their target tissues. This system is located within the plasma membrane of target cells and is responsible for the vectorial transduction of receptor occupancy by hormones into an altered rate of cyclic AMP synthesis. A complete AC system (Figure 1) responds to both stimulatory and inhibitory hormonal regulation (Cooper, 1982). In addition to receptors (R) and the catalytic unit (C), which actually synthesizes cAMP, an AC system is composed of two N (or G) coupling proteins that upon activation regulate the activity of C (Figure 2).