HiPIP in Rubrivivax gelatinosus is firmly associated to the membrane in a conformation efficient for electron transfer towards the photosynthetic reaction centre.
High potential iron-sulfur protein (HiPIP), a small soluble redox protein, has been shown to serve in vivo as electron donor to the photosynthetic reaction centre (RC) in Rubrivivax gelatinosus [Biochemistry 34 (1995) 11736]. The results of time-resolved optical spectroscopy on membrane-fragments from this organism indicates that the photooxidized RC is re-reduced by HiPIP even in the absence of the soluble fraction. This implies that a significant fraction of HiPIP can firmly bind to the membrane in a conformation able to interact with the RCs. Salt treatment of the membrane-fragments abolishes these re-reduction kinetics, demonstrating the presence of HiPIP on the membrane due to association with the RC rather than due to simple trapping in hypothetical chromatophores. The existence of such a functional complex in membranes is confirmed and its structure further examined by electron paramagnetic resonance (EPR) performed on membrane-fragments. Orientation-dependent EPR spectra of HiPIP were recorded on partially ordered membranes, oxidized either chemically or photochemically. Whereas hardly any preferential orientation of the HiPIP was seen in the chemically oxidised sample, a subpopulation of HiPIP showing specific orientations could be photooxidised. This fraction arises from the electron transfer complex between HiPIP and the RC.
Lieutaud
Clément
C
Laboratoire de Biophysique des Transporteurs d'Electrons, Faculté des Sciences de Luminy, 136 Avenue de Luminy, 13288 Marseille Cedex 9, France.
Nitschke
Wolfgang
W
Verméglio
André
A
Parot
Pierre
P
Schoepp-Cothenet
Barbara
B
D001426:Bacterial Proteins; D004578:Electron Spin Resonance Spectroscopy; D004579:Electron Transport; D007506:Iron-Sulfur Proteins / Q000737:chemistry / Q000378:metabolism*; D008027:Light; D010777:Photochemistry; D045322:Photosynthetic Reaction Center Complex Proteins / Q000737:chemistry / Q000378:metabolism*; D011487:Protein Conformation; D018717:Purple Membrane / Q000737:chemistry / Q000378:metabolism*; D013057:Spectrum Analysis / Q000379:methods; D013997:Time Factors
D001426:Bacterial Proteins; D007506:Iron-Sulfur Proteins; D045322:Photosynthetic Reaction Center Complex Proteins; C007943:high potential iron-sulfur protein