Conductance of Poly-3-hydroxybutyrate/calcium Polyphosphate Complexes in Planar Bilayers

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This proposal is to study the properties of complexed poly- hydroxybutyrate/calcium polyphosphate and non-covalently associated proteins in planar lipid bilayers. There is preliminary evidence that this membrane domain may be involved in calcium regulation, based on spectrofluorometric studies in cell cultures and single cells. The complex is widespread in prokaryotes and may be present in mitochondria of eukaryotes. It is hypothesized to act by solvating polyanionic salts and forming ion-conducting complexes which could result in the removal of calcium from the cell, with simultaneous removal of phosphate. The voltage-dependent calcium conductance of the complex from E. coli will be studied in planar lipid bilayers. The cation selectivity and the action of channel blocking agents will also be determined. %%% Bacteria contain large amounts of a complex of polyhydroxybutyrate and calcium polyphosphate. The composition of this complex suggests that the polyhydroxybutyrate could solvate polyanionic (negatively charged) complexes and allow them to move through the helical channel which is thought to be formed, thus removing calcium and polyphosphate from the interior to the exterior. This possibility can be examined by putting the complex into a planar lipid bilayer, which can be used as a model of the plasma membrane of cells, and changing the conditions in the environment. The ionic composition and the electrical charge applied will both be varied, and the effects of these variations will be assessed. It seems likely that this complex is also present in higher organisms, and may function in regulation of calcium. Since calcium concentration is very important in cellular function, these studies should be useful in understanding a new mechanism for varying intracellular calcium.