Electron transfer in the Rhodobacter sphaeroides reaction center assembled with zinc bacteriochlorophyll

Su Lin*, Paul R. Jaschke, Haiyu Wang, Mark Paddock, Aaron Tufts, James P. Allen, Federico I. Rosell, A. Grant Mauk, Neal W. Woodbury, J. Thomas Beatty

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review

23 Citations (Scopus)


The cofactor composition and electron-transfer kinetics of the reaction center (RC) from a magnesium chelatase (bchD) mutant of Rhodobacter sphaeroides were characterized. In this RC, the special pair (P) and accessory (B) bacteriochlorophyll (BChl) -binding sites contain Zn-BChl rather than BChl a. Spectroscopic measurements reveal that Zn-BChl also occupies the H sites that are normally occupied by bacteriopheophytin in wild type, and at least 1 of these Zn-BChl molecules is involved in electron transfer in intact Zn-RCs with an efficiency of >95% of the wild-type RC. The absorption spectrum of this Zn-containing RC in the near-infrared region associated with P and B is shifted from 865 to 855 nm and from 802 to 794 nm respectively, compared with wild type. The bands of P and B in the visible region are centered at 600 nm, similar to those of wild type, whereas the H-cofactors have a band at 560 nm, which is a spectral signature of monomeric Zn-BChl in organic solvent. The Zn-BChl H-cofactor spectral differences compared with the P and B positions in the visible region are proposed to be due to a difference in the 5th ligand coordinating the Zn. We suggest that this coordination is a key feature of protein-cofactor interactions, which significantly contributes to the redox midpoint potential of H and the formation of the charge-separated state, and provides a unifying explanation for the properties of the primary acceptor in photosystems I (PS1) and II (PS2).

Original languageEnglish
Pages (from-to)8537-8542
Number of pages6
JournalProceedings of the National Academy of Sciences of the United States of America
Issue number21
Publication statusPublished - 26 May 2009
Externally publishedYes


  • Magnesium chelatase mutant
  • Photosynthetic bacterial reaction center
  • Photosystems I and II
  • Protein-cofactor interaction


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