Electron paramagnetic resonance of the primary radical pair [D·+ φA·−] in reaction centers of photosynthetic bacteria

✍ Scribed by I.I. Proskuryakov; I.B. Klenina; P.J. Hore; M.K. Bosch; P. Gast; A.J. Hoff

• Publisher: Elsevier Science
• Year: 1996
• Tongue: English
• Weight: 662 KB
• Volume: 257
• Category: Article
• ISSN: 0009-2614
• DOI: 10.1016/0009-2614(96)00529-5

✦ Synopsis

Using continuous wave EPR spectroscopy with a high time resolution, a new short-lived signal at g = 2 is observed in bacterial photosynthetic reaction centers in which electron transfer past the bacteriopheophytin @A is blocked. This signal decays with a time constant equal to the rise time of the triplet state of the primary donor 3D, and is therefore attributed to the primary radical pair [D'+ @A-1. Applying the theory of spin-correlated radical pairs, the spectrum could he satisfactorily simulated, yielding the following magnetic interaction parameters between D'+ and @A-: exchange interaction Jo+ = -0.9 + 0.1 mT and Jo, = -1.7 + 0.1 mT for reaction centers of Rhodobacter sphaeroides R26 and Rhodopseudomonas viridis, respectively, and an axial dipolar interaction D,* = -3.0 + 0.5 mT for Rhodopseudomonus viridis. The implications of the magnitude and sign of the exchange parameters for the energetics of photosynthetic electron transfer are discussed.