- How does the G protein accomplish the deactivation and desensitization of the adrenergic pathway?
Any help would be great! Thanks!
Answer by some girl
hormones that use the cAMP system are:
– beta receptor uses protein Gs in this pathway
– alpha 2 receptor uses protein Gi in this pathway
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2. dopamine uses Gs and Gi
In the cAMP system, there is a receptor in the cell membrane attached to a G protein. the G protein can be stimulatory (Gs) or inhibitory (Gi). When you are using an inhibitory G protein, the union on the hormone to the receptor activates this G protein, and the Gi protein inactivates adenul cyclase attached to the membrane. this causes a decrease in cAMP levels inside a cell. cAMP is the second messenger in this pathway, and it is responsible for activating protein kinase A, which in turn phosphorylates CREB to CREB-P and induces gene expression, and protein kinase also phosphorylates enzymes within the cell to activate (or deactivate) them. When the cAMP levels decrease, none of this is done, and that is how you deactivate the adrenergic pathway via G protein.
another pathway is the PIP2 system. epinephrine alpha1 receptors are in this pathway.
there is a receptor in the cell membrane, but this time the G protein is called Gq. When the hormone attaches to the receptor, the Gq protein is activated, and it activates phospholipase C attached to the cell membrane. Phopholipase C breaks down PIP2 to form DAG and IP3. IP3 releases calcium from the endoplasmic reticulum and the calcium together with the DAG molecule activate protein kinase C. potein kinase C can indice gene expression as well as phosphorylation of enzymes, activating or deactivating them. remember, some enzymes are activated when phosphorylated and deactivated when they are dephosphorylated, while other enzymes work the other way.
These two are the two G protein pathways that are involved in the adrenergic pathway. the activity of each receptor varies according to the location.