Mössbauer Spectroscopy of the Iron-Sulfur Proteins

The Mössbauer spectra of (57)Fe in two plant ferredoxins (from spinach and Euglena) and in xanthine oxidase have been measured at a series of temperatures and magnetic fields, and are found to be similar in all three proteins. In the oxidized state the iron is nonmagnetic. In the reduced state, the iron nuclei show magnetic hyperfine interaction with an electron spin S of (1/2), producing an effective field of about 180 kG at the nuclei.