Determination of in vivo metal loading, distribution, storage and environment in biological systems: Use of X-ray synchrotron light source

Transition metals are essential nutrients to living organisms and play an important role in a variety of biochemical processes. This thesis describes the characterization of biological metal sites in intact samples, in cellular organelles and in purified proteins using X-ray fluorescence spectroscopy (XRF), an element specific detection technique. XRF microprobe studies of intact marine mussel adhesive plaques and fibers demonstrated that Fe is localized near the periphery of the fiber while Zn is localized in the hinge region. Generally Zn and Fe concentrations are negatively correlated.; XANES and EXAFS studies of the Zn environment in intact yeast demonstrated that the average Zn environment is different than the simple hexaqua-Zn 2+ species and the first shell consists of low molecular weight ligands (O or N). The first shell coordination number increases from high-Zn condition to Zn-shock condition. Possible outer shell ligation environments have also been predicted. Evidence for Zn-histidine and Zn-carboxylate outer-shell scattering interactions are found in EXAFS. No evidence for the Zn-polyphosphate interaction is found, which had been suggested in the literature as a possible ligand. Possibility of Zn-metal interaction is found in the high-Zn condition.; The in vivo metal loading of Cu,Zn-superoxide dismutase (SOD) was determined using capillary electrophoresis coupled to UV and XRF detection. Mutations in SOD are linked with the neurodegenerative disease familial Amyotrophic Lateral Schlerosis (ALS), also known as Lou Gehrig's disease. These data show for the first time that different SOD mutants are present as multiple species characterized by differences in their in vivo metal loading. The data show holoprotein, apoprotein, Zn only protein and a variety of other partially metallated species; these vary from mutant to mutant. These variations in metal loading might be directly correlated to the severity of disease onset with each particular mutant. For example, A4V mutant of SOD, which is the most common ALS mutant to date, has significantly less amount of Cu bound to it.; Finally, X-ray absorption spectroscopy was used to determine the structure of the Fe sites in mutants of thioredoxin and plant glutaredoxin. In both cases, the presence of a [2Fe-2S] cluster was confirmed.