The speciation of iron in Jurkat cells and their mitochondria was assessed using biophysical methods. Large-scale cultures were grown in medium enriched with 57Fe citrate. Mitochondria were isolated anaerobically to prevent oxidation of iron centers. M�ssbauer spectra of cells were dominated by a sextet due to ferritin. They also exhibited an intense central quadrupole doublet due to S = 0 [Fe4S4]2+ clusters and low-spin FeII heme centers. Spectra of isolated mitochondria were largely devoid of ferritin but contained the central doublet and features arising from FeIII oxyhydroxide nanoparticles. Spectra from both cells and mitochondria contained a low-intensity doublet from non-heme high-spin FeII species. A portion of these species may constitute the 'labile iron pool' proposed in cellular Fe trafficking. Such species might engage in Fenton chemistry to generate reactive oxygen species. EPR spectra of cells and mitochondria exhibited signals from reduced Fe/S clusters, and HS FeIII heme and non-heme species. The basal redox state of mitochondria within cells is reduced as monitored by heme redox states; this redox poise is unaltered during the anaerobic isolation of the organelle. Contributions from heme centers were quantified using UV-vis spectroscopy. Results were collectively assessed to estimate the concentrations of various Fe-containing species in mitochondria and whole cells � the first �ironome� profile of a human cell. 

Biophysical investigation of the "ironome" of Jurkat cells and mitochondria

245th National Meeting (2013)

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