INTERFACIAL ACTIVATION OF SOLUBLE LIPOLYTIC ENZYMES

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The goal of this research is to understand the molecular mechanics of the interfacial activity of water-soluble lipolytic enzymes. We are using NMR, QLS, SANS, and fluorescence techniques in conjunction with kinetic analyses to investigate phospholipid interactions with the nonspecific phospholipase C (PLC) and the phosphatidylinositol-specific phospholipase C(PI-PLC) form Bacillus cereus. General key problems considered include the following. (i) How do phospholipid interfaces vary in different aggregate structures, and can these variations be correlated with phospholipase activity (i.e. can we explain "interfacial activation", "substrate inhibition", "surface dilution", etc.)? (ii) What phospholipase C species? (iii) Can a unified kinetic model be developed that quantitatively accounts for phospholipase rates toward substrate as monomer, micelles, detergent mixed micelles, and bilayer vesicles? The results of these studies will allow us to understand the complex interfacial behavior of two bacterial PLC type enzymes. Since the bacterial nonspecific Plc has characteristics similar to at least on neutral mammalian PLC, the general phenomena and rationale we develop for the B. cereus enzymes may be extrapolated to the important mammalian enzymes. The latter play key roles in cellular activation including the production of inositol phosphates for intracellular Ca2+ mobilization and the generation of diglyceride for activation of protein kinase C.