Great Britain The Detection and Characterization by Electron - Paramagnetic - Resonance Spectroscopy of Iron - Sulphur Proteins and other Electron - Transport Components in Chromatophores from the Purple Bacterium Chromatium

Low-temperature e.p.r. (electron-paramagnetic-resonance) spectroscopy was used to detect electron-transport components in Chromatium chromatophores with e.p.r. signals in the g=2.00 region. High-potential iron protein (Ems.o=+325mV, where Em8.0 is the midpoint potential at pH8) and a second component (g= 1.90, Em8.o=+285mV) are oxidized in illuminated chromatophores. Two iron-sulphur proteins (g= 1.94) with Em8.o=-290mV and Em8.0=-5OmV are present. One (Em8.0=-50mV) is reduced on illumination. A component (g=1.82) with Em8.0=-135mV is photoreduced at 10°K. The midpoint potential of this component is altered by o-phenanthroline and pH. The properties of this component suggest that it is the primary electron acceptor of a photochemical system. Another component (g=1.98) also has some of the properties of a primary electron acceptor, but its function cannot be completely defined. These results show that iron-sulphur proteins are present in the electron-transport system of Chromatium and indicate their role in electron transport.