Mössbauer Studies of the Iron Atom in Cytochrome

Mössbauer spectra of the iron atom in horse-heart cytochrome c were observed in frozen solution and freeze-dried samples for both the oxidized and reduced states. At temperatures above 77°K, the spectrum of the oxidized enzyme consisted of a quadrupole-split doublet, broadened by a temperature-dependent, magnetic hyperfine interaction. The spectrum of the reduced enzyme consisted, at all temperatures observed, of two peaks with a quadrupole splitting of 0.12 cm/sec. Upon freeze drying, the quadrupole splitting of the oxidized enzyme decreased, whereas the spectrum of the reduced enzyme changed very little.