LH2 Complex from Sulfur Bacteria Allochromatium vinosum - Natural Singlet Oxygen Sensor.

It was established that in a heterogeneous model system, which consisted of two types of complexes: reaction center or core complex of photosystem 2 of higher plants and LH2 complex of the sulfur bacterium Alc. vinosum, BChl850 oxidation of the LH2 complex could be observed under illumination by the light at a wavelength of 662 nm, which is the red absorption band of Chl. It has been shown that this process induces release of singlet oxygen, which is generated in photosystem II complexes and then partially diffuses into LH2 complex, where it oxidizes BChl850.

Selective Excitation of Carotenoids of the Allochromatium vinosum Light-Harvesting LH2 Complexes Leads to Oxidation of Bacteriochlorophyll.

The mechanism of bacteriochlorophyll photooxidation in light-harvesting complexes of a number of purple photosynthetic bacteria when the complexes are excited into the carotenoid absorption bands remains unclear for many years. Here, using narrow-band laser illumination we measured action spectrum of this process for the spectral ranges of carotenoid and bacteriochlorophyll. It is shown that bacteriochlorophyll excitation results in almost no photooxidation of these molecules, while carotenoid excitation leads to oxidation with quantum yield of about 0,0003.

Chemically modified reaction centers of photosystem II: Exchange of pheophytin a with 7-deformyl-7-hydroxymethyl-pheophytin b.

The native pheophytin a (Pheo a) in isolated reaction centers of photosystem II (PSII RCs) has been chemically exchanged with extraneous 7-deformyl-7-hydroxymethyl-Pheo b (7(1)-OH-Pheo b) which differs from Pheo a by the C-7 substituent (hydroxymethyl instead of methyl). The two pigments have similar reduction potentials in vitro [M. Meyer, Dissertation, Universität München, 1997], while their absorption spectra show small but distinct differences in the visible region.