Biophysical Characterization of Iron in Mitochondria Isolated from Respiring and Fermenting Yeast

The distributions of Fe in mitochondria isolated from respiring, respiro-fermenting, and fermenting yeast cells were determined with an integrative biophysical approach involving Mössbauer and electronic absorption spectroscopies, electron paramagnetic resonance, and inductively coupled plasma emission mass spectrometry. Approximately 40% of the Fe in mitochondria from respiring cells was present in respiration-related proteins. The concentration and distribution of Fe in respiro-fermenting mitochondria, where both respiration and fermentation occur concurrently, were similar to those of respiring mitochondria. The concentration of Fe in fermenting mitochondria was also similar, but the distribution differed dramatically. Here, levels of respiration-related Fe-containing proteins were diminished ∼3-fold, while non-heme HS FeII species, non-heme mononuclear HS FeIII, and FeIII nanoparticles dominated. These changes were rationalized by a model in which the pool of non-heme HS FeII ions serves as feedstock for Fe−S cluster and heme biosynthesis. The integrative approach enabled us to estimate the concentration of respiration-related proteins.