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 ironsulfur proteins, ferredoxin from both spinach and parsley, and high potential protein from Chromafium 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 pararnagnetic with a susceptibility appropriate for a single unpaired electron per molecule of protein. The protein from Chromafium is strongly paramagnetic in the oxidized state, again with 1 unpaired electron per molecule of protein. The reduced protein is essentially diamagnetic.