Mössbauer spectroscopy - an indispensable tool in solid state research

First paragraph: More than 50 years ago, the German physicist Rudolf L. Mössbauer, whilst working on his doctoral thesis under Professor Maier-Leibnitz at the Technical University in Munich and at the Max-Planck Institute in Heidelberg, discovered the recoilless nuclear resonance absorption of gamma rays which became known as the Mössbauer Effect. He was awarded the Nobel Prize for Physics in 1961 as one of the youngest recipients of this most prestigious award. The phenomenon rapidly developed to a new spectroscopic technique, which now bears Rudolf Mössbauer's name. Mössbauer spectroscopy has made valuable contributions to widespread applications in solid state research, from fundamental studies in physics, chemistry, metallurgy, biological- and geo-sciences as well as to industrial and materials science applications. Figure 1 gives an overview of applications of Mössbauer spectroscopy in various research disciplines

Mössbauer, Electron-Paramagnetic-Resonance and X-ray-Absorption Fine-Structure Studies of the Iron Environment in Recombinant Human Tyrosine Hydroxylase

Isoforms (1 -4) of human tyrosine hydroxylase (TH) have been expressed in Escherichia coli and purified as apoenzymes (metal-free). Apo-human TH binds 1.0 atom Fe(II)/enzyme subunit, and iron binding is associated with an immediate and dramatic (40-fold) increase in specific activity. For X-ray absorption fine structure (XAFS) and electron paramagnetic resonance (EPR) measurements the apoenzyme was reconstituted with 56Fe and for Mossbauer measurements with 57Fe. XAFS measurements at the Fe-K edge of human TH were performed on the native form [Fe(II)-human TH], as well as after addition of stoichiometric amounts of the substrate tetrahydropterin, the inhibitor dopamine and of H2O2. The addition of dopamine or H2O2 oxidizes the ferrous iron of the native human TH to the ferric state. In both redox states the iron is octahedrally coordinated by low-Z backscatterers, thus sulfur coordination can be excluded. From the multiple scattering analysis of the EXAFS region is was surmised that part of the iron coordination is due to (3 ± 1) imidazols. Addition of tetrahydropterin does not significantly change the iron coordination of the Fe(II) enzyme. The Mössbauer results confirm the valence states and the octahedral coordination of iron as well as the exclusion of sulfur ligation. Both the EPR spectra and the Mossbauer magnetic hyperfine pattern of dopamine- and H2O2-treated native human TH, were analyzed with the spin-Hamiltonian formalism. This analysis provides significantly different features for the two forms of human TH: the ferric iron (S= 5/2) of the H2O2-treated form exhibits a rhombic environment while that of the dopamine-treated form exhibits near-axial symmetry. The specific spectroscopic signature of dopamine-treated human TH, including that of an earlier resonance-Raman study [Michaud-Soret, I., Andersson, K. K., Que, L. Jr & Haavik, J. (1995)Biochemistry 34, 5504–5510] is most likely due to the Biolentate binding of dopamine to iron