Question

What is the function of Phospholipase C?

• A. It attacks the ester bond in position 1 of phospholipids.
• B. It attacks the ester bond in position 2 of phospholipids.
• C. It attacks the ester bond in position 3 of phospholipids.
• D. It hydrolyzes the nitrogenous base from phospholipids.

Hint:

Phospholipase C (PLC) cleavage yields DAG and $IP_{3}$ from $PIP_{2}$.
This reaction is a key step in calcium-mediated intracellular signaling.

Answer 1

The Correct Option is C

Step 1: Understanding the Concept:
Phospholipases are a family of enzymes that hydrolyze specific ester bonds within phospholipid molecules.
Each class of phospholipase ($A_{1}$, $A_{2}$, $C$, and $D$) targets a distinct chemical bond on the phospholipid backbone.

Step 2: Detailed Explanation:
A glycerophospholipid consists of a glycerol backbone where:
Position 1 (C1) is esterified to a saturated fatty acid.
Position 2 (C2) is esterified to an unsaturated fatty acid.
Position 3 (C3) is linked to a polar head group via a phosphodiester bridge.
The cleavage sites are defined as follows:
- Phospholipase $A_{1}$ cleaves the acyl ester bond at position
- Phospholipase $A_{2}$ cleaves the acyl ester bond at position
- Phospholipase C cleaves the phosphodiester bond on the glycerol side (position 3), releasing a diacylglycerol (DAG) and a phosphorylated head group (such as inositol 1,4,5-trisphosphate, $IP_{3}$).
- Phospholipase D cleaves the ester bond on the outer side of the phosphate group, releasing the free polar head group and phosphatidic acid.
Therefore, Phospholipase C is characterized by its cleavage of the ester linkage at position 3 of the glycerol backbone.

Step 3: Final Answer:
Phospholipase C hydrolyzes the ester linkage at position 3 of phospholipids, producing diacylglycerol and a phosphorylated head group.