Photoinitiated ion movements in bilayer membranes containing magnesium octaethylporphyrin

Biophysical Journal
M Woodle, D Mauzerall

Abstract

A photocurrent produced by planar lipid bilayers containing Mg-octaethylporphyrin in the presence of oxygen has been investigated to determine if the current is due to movement of the MgOEP+ ion in the bilayer. Photoexcitation of the MgOEP is known to produce MgOEP+ in the bilayer when an electron acceptor is present. However, the aqueous electron acceptors ferricyanide and methyl viologen (MV+2) have opposite effects on the photocurrent. Ferricyanide decreases the photo current, even in the presence of oxygen, whereas methyl viologen increases the photocurrent, but only when oxygen is present. We attribute most of the photocurrent to the movement of superoxide anion. The difference in effect between ferricyanide and methyl viologen is attributed to the different rates of reduction of O2 by reduced MV+ (fast) vs. ferrocyanide (slow) and the known competition between ferricyanide and oxygen as the acceptor for the photoexcited porphyrin. It is inferred that most of the MgOEP is localized in the polar region of the lipid bilayer. Addition of ferrocyanide to the aqueous phase on one side of the bilayer, to trap MgOEP+ produced on the other side by MV+2, fails to increase the lifetime of the photovoltage. With a pH gradient across ...Continue Reading

Citations

Jul 1, 1988·Proceedings of the National Academy of Sciences of the United States of America·B ChristensenD Mauzerall
Sep 1, 1989·Proceedings of the National Academy of Sciences of the United States of America·C M DrainD Mauzerall
Oct 1, 1996·Proceedings of the National Academy of Sciences of the United States of America·K Sun, D Mauzerall
May 1, 1989·Photochemistry and Photobiology·A IlaniD Mauzerall
Oct 18, 2008·Langmuir : the ACS Journal of Surfaces and Colloids·C L BrosseauJ Lipkowski

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