The Electron Paramagnetic Resonance Spectrum at 77 °K of Lyophilized and Frozen Solutions of Horse Heart Ferricytochrome c

The electron paramagnetic resonance spectrum of a repurified, commercial preparation of horse heart ferricytochrome c was measured both in frozen solution, and as a lyophilized powder at 77 °K. The solution spectrum agreed with previous measurements reported at 20 °K. The lyophilized powder had both high-spin (g ~ 6), and low-spin components. The latter were significantly different from that of the solution spectrum. Thus, the molecular structure of the protein near the iron atom must be considerably, but reversibly, distorted by drying. In addition, it was suggested that a g = 4.29 line was due to acid-denatured forms of cytochrome c present as an impurity.