ONE-SIDED PORES FORMED BY NYSTATIN IN LIPID BILAYER MEMBRANES
KLEINBERG, MICHAEL ERIC
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The polyene antibiotic, nystatin, forms pores in eukaryotic cell membranes as well as in artificial membranes that contain sterol. In sterol-containing planar artificial bilayers, nystatin forms two types of pores. When added to only one side of the membrane, it forms cation-selective channels (the one-sided pores) yet when added simultaneously to both sides of the membrane, it forms anion-selective channels (the two-sided pores). The molecular model of Finkelstein, Holz, and Marty proposes that the one-sided pore consists of 8 - 10 nystatin monomers arranged circumferentially like the staves of a barrel with sterol molecules bound between the monomers. Two of these one-sided "barrels" joined end to end form the two-sided pore. I have tested three major predictions of this model. (1) The model assumes that the one molecular species, i.e., nystatin forms both the one- and two-sided pores. I have purified the commercial Squibb Nystatin by HPLC and shown that both pores are formed by only one of the four separated fractions. (2) The model predicts that the one-sided pore is 1/2 the thickness of the two-sided pore. I examined the activities of both pores on membranes made from a series of monoglycerides of varying acyl chain lengths. I have found that the one-sided pore forms only on the monoglyceride membranes of 18 carbon atom acyl chain length or less, while the two-sided pore forms on membranes of all thicknesses, indicating that the one-sided pore is shorter than the two-sided pore. (3) By comparing the permeability of urea and glycerol through the one- and two-sided pores, I have shown that the inner diameters of both pores are identical as predicted by the model.;In addition, I have characterized the cation-selective one-sided nystatin pore. It has a 5pS conductance in 2MKCl. My data indicate that the one-sided nystatin channels induced in artificial membranes are identical to those formed physiologically in cell membranes.;*Work completed in 1983, but degree will be granted in 1984.
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