Open AccessResponse of 9‐Aminoacridine Fluorescence to Transmembrane pH‐Gradients in Chromatophores from Rhodopseudomonas sphaeroides
Author(s) -
ELEMA Reinder P.,
MICHELS Paul A. M.,
KONINGS Wil N.
Publication year - 1978
Publication title -
european journal of biochemistry
Language(s) - English
Resource type - Journals
eISSN - 1432-1033
pISSN - 0014-2956
DOI - 10.1111/j.1432-1033.1978.tb12757.x
Subject(s) - nigericin , chemistry , quenching (fluorescence) , fluorescence , membrane , chromatophore , photochemistry , electrochemical gradient , biophysics , photosystem ii , analytical chemistry (journal) , chromatography , photosynthesis , biochemistry , physics , fishery , biology , quantum mechanics
The fluorescent probe 9‐aminoacridine interacts with the membranes of chromatophores by an energy‐independent binding and by two light‐energy‐dependent processes: a nigericin‐insensitive interaction and a nigericin‐sensitive interaction. This has been demonstrated by measurements of the medium concentration of 9‐aminoacridine by flow dialysis and by conventional fluorescence measurements. The energy‐independent and the actinic‐light‐induced nigericin‐sensitive quenching occur according to the Freundlich equation indicating adsorption of the probe to the membrane. The actinic‐light‐induced nigericin‐insensitive quenching cannot simply be described by an adsorption process. This quenching appears to be dependent on the number of probe molecules bound to the membrane independently of energy. The light‐induced nigericin‐sensitive quenching appears to be dependent on the pH‐gradient across the membrane. The observation that this quenching is the result of an adsorption excludes quantitative ΔpH determinations which are based on the assumption that the probe is entrapped inside the chromatophores. The values calculated for the ΔpH based on this assumption are dependent on protein concentration and two – three‐fold larger than those determined from the uptake of [ 14 C]methylamine as measured with the flow dialysis method.