Electron-paramagnetic-resonance spectroscopy of iron-binding fragments of hen ovotransferrins.

1. It is confirmed that there are two e.p.r. (electron-paramagnetic-resonance) signals associated with fully loaded ovotransferrin, which has two iron-binding sites. 2. Through experiments in which either of the two sites of whole ovotransferrin is occupied, the other being empty, the first occupied site is shown to belong to the N-terminal region of the protein; the second occupied site is in the C-terminal region. 3. When the protein is cleaved with trypsin or subtilisin, the N-terminal fragments are spectroscopically similar to the monoferric ovotransferrin complexes in which the iron atom occupies the N-terminal or C-terminal site respectively. Each fragment displays the same two e.p.r. signals, though not in the same proportions. 4. Computer summations of the e.p.r. spectra confirm that there is no iron-iron interaction which affects the spin Hamiltonian parameters at the iron-binding sites.