PARENT SESSION
Posters P2A Type I reaction centres. Abstracts (181-218)

Electron paramagnetic resonance spectra and protein composition of photosynthetic reaction centers from Heliobacterium modesticaldum. Mark Heinnickel^*,1, Gaozhong Shen¹, John Golbeck^{1, 2}, ¹ Department of Biochemistry and Molecular Biology, USA² Department of Chemistry, University Park, PA, USA

ABSTRACT- Heliobacteriaceae are obligately anaerobic phototrophs that contain the unique pigment bacteriochlorophyll g. Functionally, they contain Type I photosynthetic reaction centers, and similar to anaerobic green sulfur bacteria, the reaction centers are homodimeric. However, it is unclear how many low molecular mass polypeptides are present in the reaction center. It is also unclear if the same number and type of electron transfer cofactors exist as in other Type I reaction centers. To study their structure, function, and organization, we have isolated the photosynthetic reaction center from the thermophilic species Heliobacterium modesticaldum. Different detergents were used to solubilize membranes under both anaerobic and aerobic conditions. The reaction center was resolved by centrifugation on a sucrose density gradient, and further purified by DEAE ion-exchange chromatography and blue-native gel electrophoresis. The major challenge in purifying all homodimeric reaction centers is that the iron-sulfur clusters are highly sensitive to denaturation by dioxygen. Using n-octyl--D-glucopyranoside or n-dodecyl--D-maltoside, we succeeded in isolating reaction centers from H. modesticaldum with intact iron-sulfur clusters. Low temperature EPR studies show the presence of photo-inducible and oxygen-sensitive [4Fe-4S] clusters. The purified reaction centers were analyzed by SDS-PAGE. Five major protein bands were resolved and have been blotted for N-terminal sequencing. Details on the low temperature EPR spectra of the iron-sulfur clusters and the low molecular mass polypeptides will be reported. (Funded by the DOE)

KEY WORDS: Reaction Center, Heliobacteria, Iron-sulfur cluster, EPR