The reduction of inorganic iron and cytochrome c by flavin enzymes.

During the course of an investigation of the components involved in the electron transport pathway in Pseudomonas $uorescens (1)) the problem arose as to the nature of the carriers mediating the transfer of electrons between the diaphorase and bacterial cytochrome c. Mahler and Elowe (2) have reported the involvement of iron as a component of the DPNH’ cytochrome c reductase from pig heart. Removal of iron from the enzyme transformed the reductase to a diaphorase; addition of iron restored reductase activity. In view of this, it was deemed advisable to investigate the possibility of reconstituting the cytochrome c reductase of Pseudomonas by adding iron to the diaphorase rather than the usual bacterial particles or dye. The addition of ferric iron to the diaphorase did not cause a reduction of cytochrome c; however, the enzyme could reduce the ferric iron, as indicated by the orange-red color which developed when orthophenanthroline was used as a complex-forming agent. In view of subsequent work from this laboratory demonstrating that inorganic ferrous iron under appropriate conditions could reduce cytochrome c non-enzymatically (3), it became clear that reduction of cytochrome c does not necessarily indicate the reconstitution of a cytochrome c reductase from inorganic iron and a diaphorase. Any enzyme possessing the capacity to reduce ferric iron would appear to have some cytochrome c reductase activity.