26] Contact shifts and magnetic susceptibilities in iron-sulfur proteins as determined from nuclear magnetic resonance spectra

Abstract

Publisher Summary This chapter discusses the use of nuclear magnetic resonance (NMR) in the determination of the geometrical structures and the electronic and magnetic properties of the iron/sulfur/cysteine centers in the iron–sulfur proteins. Iron–sulfur proteins exhibit multiple oxidation states and generally possess low redox potentials. The redox centers of these proteins appear to be associated with the iron–sulfur moiety. At least one oxidation state of each of the iron–sulfur proteins studied is found to be paramagnetic, and has permitted a number of important and revealing electron spin resonance (ESR) and magnetic susceptibility studies. Molecular paramagnetism can produce profound effects on the characteristics of NMR. The applications to the iron-sulfur proteins rubredoxin and ferredoxin from Clostridium pasteurianum and the high potential iron protein (HiPIP) from Chromatium are illustrated in the chapter. The results on ferredoxin illustrate the remarkable spin-ordering features that appear to exist throughout the class of iron–sulfur proteins that contain two or more iron atoms per molecule. An invaluable feature of molecular paramagnetism is that its presence can give rise to contact shifts in NMR absorption that provide insight into electronic and geometrical structures of molecules, and iron–sulfur proteins.