Biophys J, October 2000, p. 2121-2131, Vol. 79, No. 4

Membrane Photopotential Generation by Interfacial Differences in the Turnover of a Photodynamic Reaction

Valerij S. Sokolov,^* Michael Block, Irina N. Stozhkova,^* and Peter Pohl

 ^*Frumkin Institute of Electrochemistry RAS, Moscow, Russia, and  Institut für Medizinische Physik und Biophysik, Martin-Luther-Universität, 06097 Halle, Germany

The adsorption of a membrane-impermeable photosensitizer to only one membrane leaflet is found to trigger a localized photodynamic reaction; i.e., the amount of carbonyl cyanide m-chlorophenylhydrazone (CCCP) molecules damaged in the leaflet facing the photosensitizer is roughly identical to the total amount of CCCP inactivated. Whereas the latter quantity is assessed from the drop in membrane conductivity G, the former is evaluated from the photopotential  that is proportional to the interfacial concentration difference of the uncoupler. Localized photodestruction is encountered by CCCP diffusion to the site of photodamage. A simple model that accounts for both photoinhibition and diffusion predicts the dependence of the photopotential on light intensity, buffer capacity, and pH of the medium. It is concluded that only a limited amount of the reactive oxygen species responsible for CCCP photodamage diffuses across the membrane. If the concentration of reactive oxygen species is decreased by addition of NaN₃ or by substituting aqueous oxygen for argon,  is inhibited. If, in contrast, their life time is increased by substitution of H₂O for D₂O,  increases.

Biophys J, October 2000, p. 2121-2131, Vol. 79, No. 4
© 2000 by the Biophysical Society   0006-3495/00/10/2121/11  $2.00