Kinetic analysis of XXXX phospholipase Ddelta. Substrate preference and mechanism of activation by @entity141 and phosphatidylinositol 4,5-biphosphate.

@entity1078 @entity958 @entity2434 @entity30847 @entity3633 @entity141
@entity30847 ( @entity30847 ) is a major plant phospholipase family involved in many cellular processes such as signal transduction, membrane remodeling, and lipid degradation. Five classes of PLDs have been identified in @entity958 , and @entity141 and polyphosphoinositides have been suggested as key regulators for these enzymes. To investigate the catalysis and regulation mechanism of individual PLDs, surface-dilution kinetics studies were carried out on the newly identified PLDdelta from @entity958 . PLDdelta activity was dependent on both bulk concentration and surface concentration of substrate phospholipids in the Triton X-100/phospholipid mixed micelles. V(max), K(s)(A), and K(m)(B) values for PLDdelta toward @entity2434 or @entity3633 were determined; @entity3633 was the preferred substrate. PLDdelta activity was stimulated greatly by @entity1078 ( @entity1078 ). Maximal activation was observed at a PIP(2) molar ratio around 0.01. Kinetic analysis indicates that PIP(2) activates @entity30847 by promoting substrate binding to the enzyme, without altering the bulk binding of the enzyme to the micelle surface. @entity141 is required for PLDdelta activity, and it significantly decreased the interfacial Michaelis constant K(m)(B). This indicates that @entity141 activates @entity30847 by promoting the binding of phospholipid substrate to the catalytic site of the enzyme.
