Allison Cockrell - Vacuoles are Reduced to the Ferrous State during Adenine-Precursor Detoxification

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      Publication Details (including relevant citation   information):

      Jinkyu Park, Sean P. McCormick,   Allison L. Cockrell, Mrinmoy Chakrabarti, and   Paul A. Lindahl (2014) Biochemistry 53 (24), 3940 –   3951


        The majority of Fe in Fe-replete yeast cells is located in   vacuoles. These acidic organelles store Fe for use under   Fe-deficient conditions and they sequester it from other parts of   the cell to avoid Fe-associated toxicity. Vacuolar Fe is   predominantly in the form of one or more magnetically isolated   nonheme high-spin (NHHS) FeIII complexes   with polyphosphate-related ligands. Some FeIII oxyhydroxide   nanoparticles may also be present in these organelles, perhaps in   equilibrium with the NHHS FeIII.   Little is known regarding the chemical properties of vacuolar Fe.   When grown on adenine-deficient medium (A↓), ADE2Δ strains of   yeast such as W303 produce a toxic intermediate in the adenine   biosynthetic pathway. This intermediate is conjugated with   glutathione and shuttled into the vacuole for detoxification. The   iron content of A↓ W303 cells was determined by Mössbauer and EPR   spectroscopies. As they transitioned from exponential growth to   stationary state, A↓ cells (supplemented with 40 μM   FeIII citrate)   accumulated two major NHHS FeII species   as the vacuolar NHHS FeIII species   declined. This is evidence that vacuoles in A↓ cells are more   reducing than those in adenine-sufficient cells. A↓ cells   suffered less oxidative stress despite the abundance of NHHS   FeIIcomplexes;   such species typically promote Fenton chemistry. Most Fe in cells   grown for 5 days with extra yeast-nitrogen-base, amino acids and   bases in minimal medium was HS FeIIIwith   insignificant amounts of nanoparticles. The vacuoles of these   cells might be more acidic than normal and can accommodate high   concentrations of HS FeIII species.   Glucose levels and rapamycin (affecting the TOR system) affected   cellular Fe content. This study illustrates the sensitivity of   cellular Fe to changes in metabolism, redox state and pH. Such   effects broaden our understanding of how Fe and overall cellular   metabolism are integrated.

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