Laser Picosecond Difference Spectrophotometry: The Problems of Excitation Dynamics in Rhodospirillum Rubrum Chromatophores

Abstract

Light quanta create the singlet excitations in the antenna chlorophyll (Chl) molecules, most of which migrate to reaction centers (RC) and initiate a primary charge separation under conditions of active photosynthesis. The remaining part of the excitations are usually lost en route by intermolecular deactivation mechnisms including fluorescence emission. Therefore, it is widely accepted that the fluorescence kinetics reflect the kinetics of excitation decay in antenna Chls mostly due to trapping in RCs. This idea was first suggested in the 1950’s [1,2]. It was elaborated quantitatively by Vredenberg and Duysens [ 3,4] who showed that the yield of Bchl fluorescence rises along with reaction center conversion to the photooxidized state in one purple and one green bacteria. In 1966, Clayton confirmed these observations in experiments with four purple bacteria [5,6]. Moreover, this author demonstrated that the fluorescence yield of the antenna BChl in all cases increased 2-3-fold when RCs were converted into the inactive state (light or chemical oxidation, treatment with strong reductant, vacuum dessication, lowering of temperature).