Lecture 22

Reaction Centers

Bacterial reaction centers

The Chime tutorials below require installation of the Chime plug-in, which works best with Netscape (version 4.5).

Photosytem II

Photosytem I and Green Sulphur bacteria

A Chime tutorial which explores the strucure of photosystem I.

Evolutionary aspects

"The phylogenetic heterogeneity of anoxygenic phototrophic bacteria has been revealed by 16S rRNA sequence analysis, the results of which have led to extensive taxonomic rearrangements within previously defined taxa of phototrophs and stimulated interest in this group of organisms. Anoxygenic photosynthetic bacteria can be found within 4 of the 12 phylogenetic lineages, and in some cases are highly related to photosynthetic members of these groups. The largest number of phototrophs are found in the class Proteobacteria. Comparative phylogenetic analysis using 23S rDNA sequences generally supports the topology obtained from 16S rDNA sequences. The photosynthetic reaction centers are conserved in all photosynthetic bacteria, and are of two types. One is shared by the Proteobacteria and Chloroflexus aurantiacus and is similar to Photosystem II of cyanobacteria, while Heliobacteria and Chlorobium and relatives possess a reaction center similar to the cyanobacterial Photosystem I. These similarities are supported by sequence analysis of core reaction center peptides, but contradict phylogenies reconstructed from rRNA sequence analysis. Genome analysis by means of physical mapping has been performed for only three species of anoxygenic phototrophs. Some conservation of operon structure and gene sequence has been found within the Proteobacteria, but does not extend to other phototrophs."

(Abstract, from Stackebrandt, E, Rainey, F.A. and Ward-Rainey, N.(1996) Anoxygenic phototrophy across the phylogenetic spectrum - current understannding and future perspectives. Arch. Microbiol. 166, 211-223.)

  1. Zouni, A., Witt, H.-T., Jan Kern, Fromme, P., Kraus, N., Saenger, W. and Orth, P. (2001) Crystal structure of photosystem II from Synechococcus elongatus at 3.8 resolution. Nature 409, 739-743.
  2. Crofts, A.R., Robinson, H.H., Andrews, K., Van Doren, S. and Berry, E. (1987) Catalytic sites for reduction and oxidation of quinones. In "Cytochrome Systems: Molecular Biology and Bioenergetics", Papa, S., Chance, B. and Ernster, L., eds. pp. 617-624, Plenum Publ., New York.
  3. Ruffle, S.V., Donnelly, D., Blundell, T.L., and Nugent, J.H.A. (1993) A three-dimensional model of the photosystem II reaction center in Pisum sativum (Pea). Photosytnhesis Research (in press).
  4. Svensson, B. (1996) Ph. D. dissertation, University of Stockholm.

©Copyright 1996, Antony Crofts, University of Illinois at Urbana-Champaign, a-crofts@uiuc.edu