Slow Charge Separation in a Minority of Reaction Centers Correlated with a Blueshift of the P860-Band in Rb. Sphaeroides

Abstract

The fluorescence decay pattern of the primary donor state 1P* in Rb. sphaeroides R26 as a function of quinone (QA) content and excitation (or detection) wavelength has been investigated with a 40ps instrumental response function. The open question, whether the fluorescence components between 40ps and 1ns originate from slow charge separation or from recombination of energetically unrelaxed P+H A - -states (HA denoting bacteriopheophytin) is addressed by comparing QA-containing reaction centers (RCs) with QA-depleted ones. The removal of QA increases the recombination fluorescence lifetime of P+H A - from about 100ps to tens of nanoseconds. The key observation reported in this paper is that the fluorescence decay components in the range of 100ps to 1ns are not affected by the P+H A - lifetime. Thus, these components reflect slow charge separation of a minority ( 10ns) exhibit no shift. So far, all RC preparations investigated show these features of a blue shifted P860-band and charge separation in the l00ps time-scale, indicating that the RCs of Rb. sphaeroides are intrinsically heterogeneous.