Phospholipase C

Phospholipase C, PLC is an enzyme that produces two second messengers inositol-1, 4, 5-triphosphate (IP₃)and diacylglycerol (DAG) by cleavage of inositol phospolipids. IP₃ in turn will trigger the release of calcium from intracellular stores, and DAG is going to activate protein kinase C (PKC)    .

There is some studies that shows that this enzyme has five groups, each group contains at least two isoforms.

1. Eta is a superfamily of 1,2
2. Beta 1,2,3 and 4 key step in the intracellular transduction of many extracellular signals, are regulated by heterotrimeric G protein-coupled receptors, Gq activates inositol phospholipid signalling pathway which in turn will activate PLC-beta enzyme.
3. Delta 1,2,3
4. Gamma 1,2 enzymes are controlled by receptor tyrosine kinases.
5. Zeta 1
   

Most of them differ in their activation. Because, they are controlled by different receptors.

Phospholipase C is a plasma membrane bound enzyme and is activated by G- protein linked signalling in a similar process to the activation of adenylyl cyclase. Once the G protein has been stimulated it activates phospholipase C which cleaves a phospholipid called phosphatidylinositol 4,5- biphosphate found in the plasma membrane lipid bilayer . This results in two products: inositol 1,4,5 triphosphate (IP₃) and diacylglycerol (DAG). IP₃ diffuses into the cytosol untill it reaches the endoplasmic reticulum where it opens calcium channels causing a release of Ca²⁺ into the cytosol. This effect can be reversed in three different ways:

1. IP₃ can form IP₂ via dephosphorylation.
2. IP₃ can be phosphorylated to form IP₄
3. Ca²⁺ is pumped out rapidly.

The other product, DAG remains in the plasma membrane due to its hydrophobic fatty chains. DAG activates protein kinase C (PKC) which then phosphorylates target proteins. PKC is activated by Ca²⁺ and diacylglycerol and is therefore called a conventional PKC. DAG can also remain in the plasma membrane as it can be cleaved again with the product acting as a signalling molecule .