THE CONTRIBUTION OF RHODOSPZRZLLUM RUBRUM FERREDOXIN II TO IN VIVO EPR SIGNALS AND ITS ROLE IN ELECTRON TRANSPORT

Abstract

Evidence is presented that Fd II, an iron‐sulfur protein containing 4 irons and 4 acid‐labile sulfurs, is responsible for a number of signals previously reported detectable in cells of R. rubrum. When oxidized, Fd II exhibits a g = 2.012 EPR signal which is readily detected in R. rubrum cells. In our hands, Fd II is photochemically reduced to an EPR‐silent product contrary to the results of other investigators. However. in the presence of reducing agents. the reduced form is apparently denatured upon freezing. The denatured form exhibits EPR signals similar to some also previously observed in whole cells. Fd II catalyzes the ascorbate‐DCPIP linked photoreduction of NAD with R. rubrum chromatophores even in the presence of an inhibitor which suppresses the formation of pH and emf gradients. This result raises the possibility of a role for Fd II in non‐cyclic electron transport in R. rubrum. Copyright © 1979, Wiley Blackwell. All rights reserved