Phosphoinositide phospholipase C (PLC, EC 3.1.4.11, triphosphoinositide phosphodiesterase, phosphoinositidase C, 1-phosphatidylinositol-4,5-bisphosphate phosphodiesterase, monophosphatidylinositol phosphodiesterase, phosphatidylinositol phospholipase C, PI-PLC, 1-phosphatidyl-D-myo-inositol-4,5-bisphosphate inositoltrisphosphohydrolase; systematic name 1-phosphatidyl-1D-myo-inositol-4,5-bisphosphate inositoltrisphosphohydrolase) is a family of eukaryotic intracellular enzymes that play an important role in signal transduction processes. These enzymes belong to a larger superfamily of Phospholipase C. Other families of phospholipase C enzymes have been identified in bacteria and trypanosomes. Phospholipases C are phosphodiesterases. Phospholipase Cs participate in phosphatidylinositol 4,5-bisphosphate (PIP2) metabolism and lipid signaling pathways in a calcium-dependent manner. At present, the family consists of six sub-families comprising a total of 13 separate isoforms that differ in their mode of activation, expression levels, catalytic regulation, cellular localization, membrane binding avidity and tissue distribution. All are capable of catalyzing the hydrolysis of PIP2 into two important second messenger molecules, which go on to alter cell responses such as proliferation, differentiation, apoptosis, cytoskeleton remodeling, vesicular trafficking, ion channel conductance, endocrine function and neurotransmission. Reaction and catalytic mechanism All family members are capable of catalyzing the hydrolysis of PIP2, a phosphatidylinositol at the inner leaflet of the plasma membrane into the two second messengers, inositol trisphosphate (IP3) and diacylglycerol (DAG). The chemical reaction may be expressed as: 1-phosphatidyl-1D-myo-inositol 4,5-bisphosphate + H2O 1D-myo-inositol 1,4,5-trisphosphate + diacylglycerol PLCs catalyze the reaction in two sequential steps. The first reaction is a phosphotransferase step that involves an intramolecular attack between the hydroxyl group at the 2' position on the inositol ring and the adjacent phosphate group resulting in a cyclic IP3 intermediate. At this point, DAG is generated. However, in the second phosphodiesterase step, the cyclic intermediate is held within the active site long enough to be attacked by a molecule of water, resulting in a final acyclic IP3 product. It should be mentioned that bacterial forms of the enzyme, which contain only the catalytic lipase domain, produce cyclic intermediates exclusively, whereas the mammalian isoforms generate predominantly the acyclic product. However, it is possible to alter experimental conditions (e.g., temperature, pH) in vitro such that some mammalian isoforms will alter the degree to which they produce mixtures of cyclic/acyclic products along with DAG. This catalytic process is tightly regulated by reversible phosphorylation of different phosphoinositides and their affinity for different regulatory proteins. Cell location Phosphoinositide phospholipase C performs its catalytic function at the plasma membrane where the substrate PIP2 is present. This membrane docking is mediated mostly by lipid-binding domains (e.g. PH domain