The Magnetic Susceptibility of Oxidized and Reduced Ferredoxins from Spinach and Parsley and the High Potential Protein from Chromatium

We have measured the magnetic susceptibility of the iron-sulfur proteins, ferredoxin from both spinach and parsley, and high potential protein from Chromatium in the oxidized and reduced state. Over the temperature range 1.4-201° K the oxidized plant proteins are either totally diamagnetic or exhibit trace paramagnetism. The reduced proteins are strongly paramagnetic with a susceptibility appropriate for a single unpaired electron per molecule of protein. The protein from Chromatium is strongly paramagnetic in the oxidized state, again with 1 unpaired electron per molecule of protein. The reduced protein is essentially diamagnetic.