The G Protein Cycle Is a Target for Certain Bacterial Toxins

The G Protein Cycle Is a Target for Certain Bacterial Toxins 

Variability in hormonal response patterns does not stop at the level of second-messenger synthesis. Thus, cyclic AMP can activate the well-known cAMP-dependent protein kinase A, but the possibility of other cAMP-respon-sive enzymes or cAMP-activated regulatory proteins should not be ruled out. The protein kinase activated by cAMP can activate a number of other enzymes. For example, in the liver, phosphorylase kinase (see fig. 24.15) is activated and catalyzes the breakdown of glycogen. In adipocytes, triacyl-glycerol lipase is activated and catalyzes the breakdown of triacylglycerols. 

One should think of the individual proteins in a multi-component hormonal response system like the parts of a machine which may play similar roles in different machines where the overall function is quite different. Each cell type may contain some but not all elements, permitting cells to respond differently to the same hormonal signal or in a similar way to different hormonal signals. 

---

The Adenylate Cyclase Pathway Is Triggered by a Membrane-Bound Receptor The G Protein Cycle Is a Target for Certain Bacterial Toxins... 

---