title: Membrane photopotential generation by interfacial differences in the turnover of a photodynamic reaction.
abstract: 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 phi 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 NaN(3) or by substituting aqueous oxygen for argon, phi is inhibited. If, in contrast, their life time is increased by substitution of H(2)O for D(2)O, phi increases.
authors.affiliation: Frumkin Institute of Electrochemistry RAS, Moscow, Russia.
authors.forename: V S
authors.initials: VS
authors.lastname: Sokolov
authors.forename: M
authors.initials: M
authors.lastname: Block
authors.forename: I N
authors.initials: IN
authors.lastname: Stozhkova
authors.forename: P
authors.initials: P
authors.lastname: Pohl
mesh_terms: D055592:Biophysical Phenomena; D001703:Biophysics; D002258:Carbonyl Cyanide m-Chlorophenyl Hydrazone / Q000737:chemistry / Q000528:radiation effects; D007211:Indoles / Q000737:chemistry / Q000528:radiation effects; D008051:Lipid Bilayers / Q000737:chemistry / Q000528:radiation effects; D008564:Membrane Potentials / Q000528:radiation effects; D008954:Models, Biological; D009942:Organometallic Compounds / Q000737:chemistry / Q000528:radiation effects; D018462:Photobiology; D010778:Photochemotherapy; D017319:Photosensitizing Agents / Q000737:chemistry* / Q000528:radiation effects
chemical_list: D007211:Indoles; D008051:Lipid Bilayers; D009942:Organometallic Compounds; D017319:Photosensitizing Agents; C048577:aluminum tetrasulfophthalocyanine; D002258:Carbonyl Cyanide m-Chlorophenyl Hydrazone