Electron Paramagnetic Resonance Evidence for a Distinction between the Two Iron-binding Sites in Transferrin and in Conalbumin

The electron paramagnetic resonance spectra of aqueous solutions of both transferrin and conalbumin have been studied as a function of increasing sodium perchlorate concentration. Characteristic changes are observed which provide direct evidence for a distinction between the two metal-binding sites under certain conditions in the naturally occurring iron derivatives of each protein. This may be of physiological importance in the case of transferrin. Differences in the behavior of the two proteins were also observed.