The location of redox centers in the profile structure of a reconstituted membrane containing a photosynthetic reaction center-cytochrome c complex by resonance X-ray diffraction

Abstract

The technique of resonance X-ray diffraction (Blasie, J.K. and Stamatoff, J. (1981) Annu. Rev. Biophys. Bioeng. 10, 451–452) utilizing synchrotron radiation was used to determine the locations of the cytochrome c heme iron atom and the photosynthetic reaction center iron atom within the profile of a reconstituted membrane. The accuracy of these determinations was better than ±2 Ȧ. The cytochrome c heme iron atom → reaction center iron atom vector was determined to have a magnitude of approx. 44 Ȧ projected onto the membrane profile and to span most of the lipid hydrocarbon core of the membrane profile. Since the reaction center iron atom interacts magnetically with the primary quinone electron acceptor Q I over a distance of less than 10 Ȧ, the primary light-induced electron-transfer reactions for this system generate the electric charge separation between oxidized cytochrome c + and Fe-Q − I across most (approx. 2 3 ) of the membrane profile including most or all of the lipid hydrocarbon core of the membrane.