Fluorescence Change Of Auramine O Bound to Chromatophores of Rhodospirillum rubrum — Analysis in Connection to Ionic Environment and Ion Transport

Abstract

Auramine O [bis(p-dimethylaminophenyl)-methylenimine hydrochloride] had a very low fluorescence yield in water but the yield was markedly enhanced when bound to chromatophores of a photosynthetic bacterium, Rhodospirillum rubrum (blue-green mutant). This binding was sensitive to pH, and type and concentration of cations in the suspending medium. Fluorescence intensity of membrane-bound auramine O decreased moderately in the presence of monovalent cations (Na+, K+ or NH4+) and more significantly in the presence of divalent cations (Mg2+, Ca2+ or Mn2+) The fluorescence intensity of bound auramine O decreased reversibly by illumination of chromatophores. The time-course of the illumination-induced fluorescence change was separated into rapid and slow phases. The extent of the rapid phase was increased by addition of tetraphenylboron−; or valinomycin plus K+. The relationship between the rapid phase of the fluorescence change and the light-induced H+ transport of chromatophores was suggested. The appearance of the rapid phase was also dependent on the redox level of chromatophores. Auramine O fluorescence can be used as a probe for the survey of the physical parameters of chromatophore membranes (distribution and number of charged groups and ionic environment) and energetical level of membranes in energy transduction.