Receptor and effector systems

GTP Binding Proteins Act as Transducers between Receptors and Effector Systems... 

For a cell surface receptor, the binding of the hormone must change the activity of an effector system that results in a change in concentration of an intracellular messenger. This is achieved by location of the effector system on the cytosolic side of the membrane, although the receptor and effector system may be combined in one complex. 

Three distinct G-proteins have been fully characterized. These are transducin (T), which allows rhodopsin to stimulate a high-affinity cyclic GMP phosphodiesterase upon photoactivation in retinal rods Gs, which allows receptors to stimulate the activity of adenylate cyclase and Gh which allows receptors to inhibit adenylate cyclase activity. These three G-proteins contain three non-identical subunits (a, /3 and y). It is their a subunits which provide the binding site for GTP as well as distinct sites for interaction with specific receptor and effector systems and for Mg2+. The /3 subunits associated with all three regulatory proteins are apparently identical although T has a different y subunit. 

Figure 8. Assessment of centraly autonomic, neuromuscular, cardiovascular, respiratory, and neurohumoral receptor and effector systems...

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See also in sourсe #XX -- [ ]

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