The Gi-protein as a Target for Receptor-Receptor Interactions
The hormone-sensitive adenylate cyclase system, which serves as a transmembrane signal transduction system for a wide variety of hormones and neurotransmitters, is a dually regulated signalling system. On the one hand, many hormonal agents, after interaction with their specific receptors, cause an increase in cyclic AMP formation by the adenylate cyclase. This action is mediated by the stimulatory guanine nucleotide-binding regulatory component Gs, which transfers the information from the hormone-activated receptor to the adenylate cyclase. On the other hand, a similarly large number of hormonal agents, after interaction with their specific receptors, induce inhibition of cyclic AMP formation by the adenylate cyclase. This action involves the coupling function of the inhibitory guanine nucleotide-binding regulatory component Gi. Thus, the hormone-sensitive adenylate cyclase by itself is a system exhibiting receptor-receptor interaction, at least at the level of the adenylate cyclase, in that the action of one receptor (stimulatory or inhibitory to the adenylate cyclase) on cyclic AMP formation can be modulated by activation of another set of receptors (inhibitory or stimulatory to the adenylate cyclase).
KeywordsAdenylate Cyclase Human Platelet Pertussis Toxin Adenylate Cyclase Activity Adenylate Cyclase System
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