[Isolation and characterization of pigment-protein complexes from Rhodobacter azotoformans]

In order to reveal the relationships of compositions and content of pigment in pigment-protein complexes (PPC) and hydrogen photoevolution from anoxygenic phototrophic bacteria.

We isolated and identified pigment-protein complexes using a separation strategy of subsequent fractionated ammonium-sulfate precipitation, ion exchange column chromatography, absorption spectra and sodium dodecylsulfate polyacrylamide gel electrophoresis (SDS-PAGE) from hydrogen-producing Rhodobacter azotoformans R7. We investigated the characterizations of the peripheral light-harvesting complex (LH2) with an unusual absorption spectrum by surface enhanced laser desorption/ionization time of flight mass spectrometry (SELDI-TOF-MS), high performance liquid chromatography-mass spectrometry (HPLC-MS) and fluorescence spectra.

We acquired three types of PPC, the reaction center and core light-harvesting complex (RC-LH1) and two kinds of LH2, from strain R7 incubated anaerobically in the light. The two LH2 showed the different absorption spectra, one of them displayed unusual absorption spectrum with the maximum absorption band at 423 nm. The unusual LH2 consisted of two kinds of protein subunits with the molecular weight of 5556.8 Da and 5697.8 Da and carotenoid of spheroidene series with the molecular weight of 562 Da. It was also capable of transferring energy from carotenoid to bacterialcholorophyll and from B800 bacterialcholorophyll to B850 bacterialcholorophyll.

Rhodobacter azotoformans R7 with hydrogen-producing capacity could photosynthesize two types of LH2 under anaerobically in the light, one of them presented novel spectral property.