A time-resolved iron-specific X-ray absorption experiment yields no evidence for an Fe2+ --> Fe3+ transition during QA- --> QB electron transfer in the photosynthetic reaction center.
Previous time-resolved FTIR measurements suggested the involvement of an intermediary component in the electron transfer step Q(A)- --> Q(B) in the photosynthetic reaction center (RC) from Rhodobacter sphaeroides [Remy and Gerwert (2003) Nat. Struct. Biol. 10, 637]. By a kinetic X-ray absorption experiment at the Fe K-edge we investigated whether oxidation occurs at the ferric non-heme iron located between the two quinones. In isolated reaction centers with a high content of functional Q(B), at a time resolution of 30 micros and at room temperature, no evidence for transient oxidation of Fe was obtained. However, small X-ray transients occurred, in a similar micro- to millisecond time range as in the IR experiments, which may point to changes in the Fe ligand environment due to the charges on Q(A)- and Q(B)-. In addition, VIS measurements agree with the IR data and do not exclude an intermediate in the Q(A)- --> Q(B) transition.
Hermes
Sabine
S
Lehrstuhl für Biophysik, ND 04/596, Ruhr-Universität Bochum, D-44801 Bochum, Germany.
Bremm
Oliver
O
Garczarek
Florian
F
Derrien
Valerie
V
Liebisch
Peter
P
Loja
Paola
P
Sebban
Pierre
P
Gerwert
Klaus
K
Haumann
Michael
M
D004579:Electron Transport; D005290:Ferric Compounds / Q000737:chemistry / Q000378:metabolism*; D005296:Ferrous Compounds / Q000737:chemistry / Q000378:metabolism*; D008345:Manganese / Q000378:metabolism; D010084:Oxidation-Reduction; D045322:Photosynthetic Reaction Center Complex Proteins / Q000737:chemistry* / Q000378:metabolism*; D012242:Rhodobacter sphaeroides / Q000737:chemistry / Q000378:metabolism; D013057:Spectrum Analysis; D014451:Ubiquinone / Q000737:chemistry / Q000378:metabolism*; D014965:X-Rays
D005290:Ferric Compounds; D005296:Ferrous Compounds; D045322:Photosynthetic Reaction Center Complex Proteins; D014451:Ubiquinone; D008345:Manganese