Chemical proprieties of the iron-quinone complex in mutated reaction centers of Rb. sphaeroides

Abstract

We investigated type II bacterial photosynthetic reaction centers, which contain a quinone -iron complex (Q A -Fe-Q B ) on their acceptor side. Under physiological conditions it was observed mainly in a reduced high spin state but its low spin ferrous states were also observed. Therefore, it was suggested that it might regulate the dynamical properties of the iron-quinone complex and the protonation and deprotonation events in its neighbourhood. In order to get insight into the molecular mechanism of the NHFe low spin state formation, we preformed Mössbauer studies of a wild type of Rb. sphaeroides and its two mutated forms. Our Mössbauer measurements show that the hydrophobicity of the Q A binding site can be crucial for stabilization of the high spin ferrous state of NHFe.

On the Nature of the Hydrogen Bonds to Neutral Ubiquinone in the QABinding Site in Purple Bacterial Photosynthetic Reaction Centers

“…All heavy atoms, except those of UQ, are fixed in position, and the total charge of the 99 atoms in the QM level is set to zero (calculation 3 in Table 1). The high spin (S = 2) state of Fe is also chosen 29,30 (multiplicity of the model system is 4). In calculation 3 upon optimization, the NPA calculated charge on the UQ atoms is −0.874.…”