FLUCTUATIONAL TUNNEL EFFECTS AND VIBRATIONAL DISPERSION IN PRIMARY ELECTRON-TRANSFER PROCESSES OF BACTERIAL PHOTOSYNTHESIS

We have investigated forward electron transfer (ET) from reduced bacte riopheophytin (bph(-)) to the primary quinone (Q(A)), and the recombin ation ET from Q(A)(-) to the oxidized special pair (bch)(2)(+) in the photosynthetic reaction centre of Rh. sphaeroides. The same reactant, Q(A), is here engaged in two ET reactions of widely different distance s. The processes can also be followed over broad temperature ranges. F ocus is on two elements not commonly considered in ET theory. One is c ontinuous environmental dielectric dispersion which is both formally a nd physically important. The other one is environmental fluctuational modulation of the tunnel factor which is important when the donor and acceptor are separated by environmental matter. The analysis shows, fi rst that a broad dielectric dispersion is in line with the ET data up to approximate to 180 degrees K. Fluctuational modulation of the tunne l factor is, secondly, unimportant in shorter-rang forward ET from bph (-) to Q(A) (13 Angstrom centre-to-centre distance) but could be impor tant in the much longer-range recombination ET from Q(A)(-) to (bCh)(2 )(+) (28 Angstrom). (C) 1998 Elsevier Science B.V. All rights reserved .