BINDING OF IRON TO NEUROMELANIN OF HUMAN SUBSTANTIA-NIGRA AND SYNTHETIC MELANIN - AN ELECTRON-PARAMAGNETIC-RESONANCE SPECTROSCOPY STUDY

The binding of iron by melanin is a potentially important phenomenon a s detailed knowledge of this binding is essential for understanding th e role of melanin and iron in the pathogenesis of oxidative damage in the substantia nigra. Electron paramagnetic resonance spectroscopy is one of the most useful approaches in the investigation of melanins and their interaction with iron. This study was undertaken to obtain syst ematic data on the effects of ferric iron on the electron paramagnetic resonance spectra of neuromelanin and synthetic models of neuromelani n. Data from the latter can potentially be used to infer as to the sta te of neuromelanin in the human substantia nigra. The results of this study indicate that the spectra at g = 4.3, attributable to Fe3+, prov ides a useful parameter for determining the amount of paramagnetic iro n bound to melanin. These data together with the magnitude of the free radical signal from melanin provides an indication of the amount of i ron bound to neuromelanin in intact human substantia nigra. After bind ing to melanin, the iron can change its location and/or state, which i s indicated by the change in the microwave power saturation that occur s gradually after the binding of the iron. At least part of this proce ss could occur at low temperatures (i.e., during storage at -15 degree s C). (C) 1997 Elsevier Science Inc.