ELECTRON-PARAMAGNETIC-RESONANCE SPECTROSCOPY OF IRON COMPLEXES AND IRON-CONTAINING PROTEINS

Among the transition metal ions in biochemistry, iron has the richest variety of electron paramagnetic resonance (EPR) spectra. These include spectra of low-spin and high-spin ferric iron and of metal clusters. This chapter discusses practical aspects of the detection, identification, and quantitation of iron-containing proteins in biochemical systems, including enzymes, other proteins, and whole tissues. The principle of EPR spectroscopy is similar to that of nuclear magnetic resonance (NMR), but using electrons instead of nuclear spins. The unpaired electrons lead to paramagnetism in the sample. The differences between the two techniques are mainly because of the much larger magnetic moment of the electron, compared with the proton. This allows a considerable enhancement of the microwave field, and hence sensitivity, but prevents the acquisition of a spectrum in the conventional way by measuring absorption as a function of frequency. © 1993, Elsevier Inc. All rights reserved.