Phosphoinositide pathway — enzyme that cleaves PIP2 Which enzyme catalyzes the splitting of phosphatidylinositol 4,5-bisphosphate (PIP2) into inositol trisphosphate (IP3) and diacylglycerol (DAG) during cell signaling?

Introduction:
The phosphoinositide signaling pathway is a cornerstone of GPCR and receptor tyrosine kinase signaling. A membrane-associated enzyme cleaves PIP2 to generate two pivotal second messengers: IP3 and DAG, which together mobilize Ca2+ and activate protein kinase C (PKC).

Given Data / Assumptions:

• PIP2 resides in the inner leaflet of the plasma membrane.
• Upon receptor activation, a dedicated lipase cleaves PIP2.
• The products are IP3 (diffusible) and DAG (membrane-retained).

Concept / Approach:

Phospholipase C (PLC), particularly PLC-β or PLC-γ isoforms depending on receptor class, hydrolyzes PIP2. IP3 opens IP3-gated Ca2+ channels in the endoplasmic reticulum, while DAG recruits and activates PKC at the membrane, coordinating downstream responses.

Step-by-Step Solution:

Verification / Alternative check:

Biochemical assays directly measure PLC-dependent PIP2 hydrolysis and the resulting rise in IP3/Ca2+ and PKC activation.

Why Other Options Are Wrong:

Protein kinase C is a downstream effector activated by DAG and Ca2+, not the enzyme that cleaves PIP2.

Phosphodiesterases degrade cyclic nucleotides (cAMP/cGMP), not PIP2.

Lipokinase is not the canonical enzyme for this reaction.

Adenylyl cyclase synthesizes cAMP from ATP, unrelated to PIP2 cleavage.

Common Pitfalls:

Confusing the generator of second messengers (PLC) with the kinases activated by those messengers (PKC).

Final Answer:

Phospholipase C