Long-lived charge-separated states in bacterial reaction centers isolated from Rhodobacter sphaeroides

We studied the accumulation of long-lived charge-separated states in reacti on centers isolated from Rhodobacter sphaeroides, using continuous illumina tion, or trains of single-turnover flashes. We found that under both condit ions a long-lived state was produced with a quantum yield of about 1%. This long-lived species resembles the normal P(+)Q(-) state in all respects, bu t has a lifetime of several minutes. Under continuous illumination the long -lived state can be accumulated, leading to close to full conversion of the reaction centers into this state. The lifetime of this accumulated state v aries from a few minutes up to more than 20 min, and depends on the illumin ation history. Surprisingly, the lifetime and quantum yield do not depend o n the presence of the secondary quinone, Q(B). Under oxygen-free conditions the accumulation was reversible, no changes in the normal recombination ti mes were observed due to the intense illumination. The long-lived state is responsible for most of the dark adaptation and hysteresis effects observed in room temperature experiments. A simple method for quinone extraction an d reconstitution was developed. (C) 2001 Elsevier Science B.V. All rights r eserved.