ABSTRACT: The shape of the EPR spectrum of the triplet state of photosystem II reaction centers with a singly reduced primary acceptor
complex QAFe2+ was studied. It was shown that the spectroscopic properties do not significantly change when the relaxation of the primary
acceptor is accelerated and when the magnetic interaction between the reduced quinone molecule QA and the nonheme iron ion Fe2+ is disrupted. This observation confirmed the earlier conclusion that the anisotropy of the quantum yield of the triplet state
is the main cause of the anomalous shape of the EPR spectrum. A scheme of primary processes in photosystem II that is consistent
with the observed properties of the EPR spectrum of the triplet state is discussed.
Biophysics 01/2007; 52(1):40-45.
Doklady Biophysics 370-372:4-8.
Doklady Biochemistry and Biophysics 441:290-3. · 0.33 Impact Factor
ABSTRACT: Time-resolved cw EPR measurements of the Rhodobacter (Rb) sphaeroides R-26 reaction center primary donor triplet state excited with plane-polarised light are reported. The pigment composition of the reaction center was chemically modified, so that the bacteriopheophytin molecule in the cofactor branch which is inactive towards electron transfer was replaced by plant pheophytin a. This enabled selective excitation of the bacteriopheophytin and pheophytin molecules, and provided conditions for a high-quality magnetophotoselection study. For the first time, orientation of the Qy optical transition dipole moment relative to the molecular frame of the bacteriopheophytin in the active cofactor branch is determined. Of the four orientations allowed by magnetophotoselection, one was chosen as the most plausible. The corresponding Qy vector is tilted from the bacteriopheophytin tetrapyrrole plane by 15°, and projects onto this plane almost on the y-molecular axis. It is suggested that the deviation of the vector from the molecular plane results from an interaction of bacteriopheophytin with the neighbouring molecule of accessory bacteriochlorophyll.
Chemical Physics. 294(3):451-458.