Showing papers by "Ileana Dragutan published in 1986"

[55] Measurement of transmembrane proton movements with nitroxide spin probes

Abstract: Publisher Summary This chapter explores the way nitroxide spin probes employed to study the permeability of halobacterial envelope vesicle and erythrocyte membranes to spin-labeled weakly polar molecules, ions, amines, and weak acids Membrane proton pumps, such as bacteriorhodopsin, generate electrochemical potentials that can be measured with a combination of probes responsive to transmembrane electrical and pH gradients Weakly polar spin probes with fewer than two hydrogen-bonding residues permeate most membranes too rapidly to measure with available stop-flow electron spin resonance (ESR) techniques One of the nitroxides, 4-oxo-2,2,6,6,-tetramethylpiperidine- N -oxyl (TEMPONE), is used to measure volume changes in many envelope and cell preparations and permeates at least one cell appreciably more rapidly than water does Improved biophysical techniques are needed that will give higher resolution in space and time of the initial cascade of energy-conserving reactions or structural changes The spin-probe approach for improving the kinetics and spatial resolution of the measurements of electrochemical potentials across biological membranes is discussed in the chapter It also discusses the volume measurement technique, proton gradients, and electrical potentials Phosphonium probes, which excessively slow diffusion, invariably distort measurements The syntheses of other hydrophobic spin-labeled ions with the goal of improving the permeability constants, and thus reducing errors are required