FoundationalConceptsNeuroscience

> Neurotransmitter molecules

Effector enzyme

(adenylate cyclase)

G-protein

G-protein subunits

Protein kinase

—————— cAMP

Substrate protein @c

Figure 6.6. An intracellular cascade resulting from activating a G-protein-

coupled receptor (GPCR), with adenylate cyclase as the effector enzyme. Sub-

strate proteins are targets of phosphorylation by protein kinases. Examples

Cellular effects

of substrates are channel proteins (which would be located in the cell mem-
brane) and transcription factor proteins.

Here’s another thing: depending upon the type of cell, G-proteins
can and do interact with other things besides adenylate cyclase.
One alternative is guanylate cyclase, the enzyme that catalyzes the
synthesis of cGMP, a chemical relative of cAMP that can have simi-
lar functions inside a cell. Another is the enzyme phospholipase C,
an enzyme that catalyzes the cleavage of a particular phospholipid
(phosphatidylinositol) in the cell membrane to form two product
molecules, IP3 (inositol triphosphate) and DAG (diacylglycerol). IP3