Spectroscopic evidence for the presence of an iron-sulfur center similar to Fx of Photosystem I inHeliobacillus mobilis |
| |
Authors: | Frank A M Kleinherenbrink Hung-Cheng Chiou Russell LoBrutto Robert E Blankenship |
| |
Institution: | (1) Department of Chemistry and Biochemistry, Arizona State University, 85287-1604 Tempe, AZ, USA;(2) Department of Botany, Arizona State University, 85287-1604 Tempe, AZ, USA;(3) Center for the Study of Early Events in Photosynthesis, Arizona State University, 85287-1604 Tempe, AZ, USA |
| |
Abstract: | Treatment of membranes ofHeliobacillus mobilis with high concentrations of the chaotropic agent urea resulted in the removal of the iron-sulfur centers FA and FB from the reaction center, as indicated by EPR spectra under strongly reducing conditions. In urea-treated membranes, transient absorption measurements upon a laser flash indicated a recombination between the photo-oxidized primary donor P798+ and a reduced acceptor with a time constant of 20 ms at room temperature. Benzylviologen, vitamin K-3 and methylene blue were found to accept electrons from the reduced acceptor efficiently. A differential extinction coefficient of 225–240 mM–1 cm–1 at 798 nm was determined from experiments in the presence of methylene blue. Transient absorption difference spectra between 400 and 500 nm in the presence and absence of artificial acceptors indicated that the electron acceptor involved in the 20 ms recombination has an absorption spectrum similar to that of an iron-sulfur center. This iron-sulfur center was assigned to be analogous to FX of Photosystem I. Our results provide evidence in support of the presence of FX in heliobacteria, which was proposed on the basis of the reaction center polypeptide sequence (Liebl et al. (1993) Proc. Natl. Acad. Sci. USA 90: 7124–7128). Implications for the electron transfer pathway in the reaction center of heliobacteria are discussed. |
| |
Keywords: | photosynthesis bacteriochlorophyll electron acceptor iron-sulfur center Photosystem I heliobacteria |
本文献已被 PubMed SpringerLink 等数据库收录! |
|