Figure 15-36. The two branches of the inositol phospholipid pathway.

Figure 15-36The two branches of the inositol phospholipid pathway

The activated receptor stimulates the plasma-membrane-bound enzyme phospholipase C-β via a G protein. Depending on the isoform of the enzyme, it may be activated by the α subunit of Gq as shown, by the βγ complex of another G protein, or by both. Two intracellular messenger molecules are produced when PI(4,5)P2 is hydrolyzed by the activated phospholipase C-β. Inositol 1,4,5-trisphosphate (IP3) diffuses through the cytosol and releases Ca2+ from the endoplasmic reticulum by binding to and opening IP3-gated Ca2+-release channels in the endoplasmic reticulum membrane. The large electrochemical gradient for Ca2+ across this membrane causes Ca2+ to escape into the cytosol. Diacylglycerol remains in the plasma membrane and, together with phosphatidylserine (not shown) and Ca2+, helps to activate the enzyme protein kinase C, which is recruited from the cytosol to the cytosolic face of the plasma membrane. Of the 11 or more distinct isoforms of PKC in mammals, at least four are activated by diacylglycerol.

From: Signaling through G-Protein-Linked Cell-Surface Receptors

Cover of Molecular Biology of the Cell
Molecular Biology of the Cell. 4th edition.
Alberts B, Johnson A, Lewis J, et al.
New York: Garland Science; 2002.
Copyright © 2002, Bruce Alberts, Alexander Johnson, Julian Lewis, Martin Raff, Keith Roberts, and Peter Walter; Copyright © 1983, 1989, 1994, Bruce Alberts, Dennis Bray, Julian Lewis, Martin Raff, Keith Roberts, and James D. Watson .

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