Ba. Heller et al., CONTROL OF ELECTRON-TRANSFER BETWEEN THE L-SIDE AND M-SIDE OF PHOTOSYNTHETIC REACTION CENTERS, Science, 269(5226), 1995, pp. 940-945
An aspartic acid residue has been introduced near ring V of the L-side
accessory bacteriochlorophyll (BChl(L)) of the photosynthetic reactio
n center in a Rhodobacter capsulatus mutant in which a His also replac
es Leu 212 on the M-polypeptide. The initial stage of charge separatio
n in the G(M201)D/L(M212)H double mutant yields similar to 70 percent
electron transfer to the L-side cofactors, similar to 15 percent rapid
deactivation to the ground state, and similar to 15 percent electron
transfer to the so-called inactive M-side bacteriopheophytin (BPh(M)).
It is suggested here that the Asp introduced at M201 modulates the re
duction potential of BChl(L), thereby changing the energetics of charg
e separation. The results demonstrate that an individual amino acid re
sidue can, through its influence on the free energies of the charge-se
parated states, effectively dictate the balance between the forward el
ectron transfer reactions on the L-side of the RC, the charge-recombin
ation processes, and electron transfer to the M-side chromophores.