PLC catalyzes the hydrolysis of phosphatidyl inositol (4,5) bisphosphate (PIP2) on the cytoplasmic side of the cell membrane to yield diacylglycerol and inositol-1,4,5-triphosphate (IP3). This reaction initiates a well-known signal transduction pathway common to most cells. PLC thio-PIP2 is an analog of naturally occurring PIP2 that contains sulfur rather than oxygen at the sn-3 position of the glycerol backbone. Hydrolysis by PLC yields a free thiol which reacts with chromogenic reagents such as DTNB (Ellman’s reagent) to allow quantitation of PLC activity.