The cellular plasma membrane contains highly specialized systems for integration, amplification, and transduction of information that presents itself in the form of extracellular hormones, neurotransmitters, other regulatory molecules, and physical stimuli. A major mechanism for processing this information involves the sequential interactions of three membrane-bound proteins. Receptors for many extracellular regulators bind these molecules and interact with one or more of a family of guanine nucleotide—binding regulatory proteins (G proteins). Conformational alteration of the G protein permits exchange of tightly bound guanosine diphosphate (an inactive ligand) for guanosine triphosphate (the activating ligand). The guanosine triphosphate—bound G protein in turn interacts with intracellular effector molecules, such as adenylyl cyclase, and controls their functions.
Gilman AG. G Proteins and Regulation of Adenylyl Cyclase. JAMA. 1989;262(13):1819–1825. doi:10.1001/jama.1989.03430130095041
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