Photoinduced transient absorbance spectra of P840/P840(+) and the FMO protein in reaction centers of Chlorobium vibrioforme.
The kinetics of photoinduced absorbance changes in the 400-ns to 100-ms time range were studied between 770 and 1025 nm in reaction center core (RCC) complexes isolated from the green sulfur bacterium Chlorobium vibrioforme. A global, multiple stretched-exponential analysis shows the presence of two distinct but strongly overlapping spectra. The spectrum of the 70-micros component consists of a broad bleaching with two minima at 810 and 825 nm and a broad positive band at wavelengths greater than 865 nm and is assigned to the decay of (3)Bchl a of the Fenna-Matthews-Olson (FMO) protein. The contribution of the 70-micros component correlates with the amount of FMO protein in the isolated RCC complex. The spectrum of the 1.6-micros component has a sharp bleaching at 835 nm, a maximum at 805 nm, a broad positive band at wavelengths higher than 865 nm, and a broad negative band at wavelengths higher than 960 nm. When the RCC is incubated with inorganic iron and sulfur, the 1.6-micros component is replaced by a component with a lifetime of approximately 40 micros, consistent with the reconstruction of the F(X) cluster. We propose that the 1.6-micros component results from charge recombination between P840(+) and an intermediate electron acceptor operating between A(0) and F(X). Our studies in Chlorobium RCCs show that approaches that employ a single wavelength in the measurement of absorption changes have inherent limitations and that a global kinetic analysis at multiple wavelengths in the near-infrared is required to reliably separate absorption changes due to P840/P840(+) from the decay of (3)Bchl a in the FMO protein.
Vassiliev
I R
IR
Department of Biochemistry and Molecular Biology, The Pennsylvania State University, University Park, Pennsylvania 16802, USA.
Kjaer
B
B
Schorner
G L
GL
Scheller
H V
HV
Golbeck
J H
JH
D001426:Bacterial Proteins; D019414:Chlorobi / Q000378:metabolism*; D005292:Ferricyanides / Q000378:metabolism; D007501:Iron / Q000378:metabolism; D007700:Kinetics; D045342:Light-Harvesting Protein Complexes; D010777:Photochemistry; D045322:Photosynthetic Reaction Center Complex Proteins / Q000737:chemistry* / Q000378:metabolism*; D013057:Spectrum Analysis; D013455:Sulfur / Q000378:metabolism; D013997:Time Factors
D001426:Bacterial Proteins; C086320:FMO bacteriochlorophyll protein, Bacteria; D005292:Ferricyanides; D045342:Light-Harvesting Protein Complexes; D045322:Photosynthetic Reaction Center Complex Proteins; D013455:Sulfur; D007501:Iron; C028033:potassium ferricyanide