Divalent Cations, Electrostatic Potentials, Bilayer Membranes
“How many? How tightly? Where? Why?” these were the questions posed by Scatchard (1949) in his elegant study of the adsorption of ions to proteins. These succinct questions also define what we wish to know about the adsorption of divalent cations to phospholipid bilayer membranes. The first two questions, which relate to the stoichiometry of the binding and the magnitude of the binding constants, will be addressed in this chapter. The third question, which relates to the exact location of the bound divalent cations in the phospholipid head group, requires a molecular approach such as nuclear magnetic resonance (NMR) and will be addressed in the following chapter. The fourth question, which relates to the physiological relevance of the adsorption of divalent cations to the bilayer component of biological membranes, cannot yet be completely answered. We shall, however, consider two phenomena: (1) the effect of divalent cations on the electrostatic potential at the surface of a nerve membrane and (2) the effect of the adsorption of calcium to intracellular membranes on the diffusion coefficient of this ion.
KeywordsNuclear Magnetic Resonance Electron Spin Resonance Divalent Cation Electrostatic Potential Bilayer Membrane
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