The membrane-extrinsic domain of cytochrome b(558/566) from the Archaeon Sulfolobus acidocaldarius performs pivoting movements with respect to the membrane surface

The orientation of the membrane-attached cytochrome b(558/566)-haem with re spect to the membrane was determined by electron paramagnetic resonance spe ctroscopy on two-dimensionally ordered oxidised membrane fragments from Sul folobus acidocaldarius. Unlike the other redox centres in the membrane, the cytochrome b(558/566)-haem mas found to cover a range of orientations betw een 25 degrees and 90 degrees. The described results are reminiscent of tho se obtained on the Rieske cluster of bc complexes and indicate that the mem brane-extrinsic domain of cytochrome b(558/566) can perform pivoting motion between two extreme positions. Such a conformational flexibility is likely to play a role in electron transfer with its redox partners. (C) 2001 Fede ration of European Biochemical Societies. Published by Elsevier Science B.V . All rights reserved.