Roles of proteins in the electron transfer in the photosynthetic reaction center of Rhodopseudomonas viridis: bacteriopheophytin to ubiquinone

The electron transfer (ET) from bacteriopheophytin (H) to ubiquinone (UQ) in the photosynthetic reaction center (PSRC) of Rhodopseudomonas (Rps.) viridis was studied by ab initio quantum-chemical calculations. The ET from the H in L-region (HL) to menaquinone (MQ) occurs through the super-exchange mechanism using Trp M250 as a bridge, while in the M-region Leu L189 works as a bridge in the ET from HM to UQ. The transfer integral for the L-branch was 20 times larger than that for the M-branch, which was due to the difference in the amino acid residues placed between the chromophores. For the ET from MQ to UQ, the super-exchange mechanism using His M217 and His L190 as two subsequent bridges was by far the largest, showing the importance of these residues in the ET between MQ and UQ. c © 2001 John Wiley & Sons, Inc. J Comput Chem 22: 265–272, 2001