High-Spin Ferric Ions in Saccharomyces cerevisiae Vacuoles Are Reduced to the Ferrous State during Adenine-Precursor Detoxification

Abstract

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 FeII complexes; 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 FeIII with 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.

Iron Absorption from Iron-Enriched Aspergillus oryzae Is Similar to Ferrous Sulfate in Healthy Female Subjects

“…It is widely used to produce food-grade enzymes, rice vinegars, miso, and soy sauce and is consumed by a wide range of the population ( 18 , 19 ). Most fungi have the ability to acquire small amounts of iron for their own survival, sequester iron mostly in vacuoles ( 20 ), and later mobilize it for cellular usage ( 21 ). However, A. oryzae can take up significantly higher amounts of iron than other fungi, providing a superior alternative to yeast for food fortification ( 22 ).…”

Mitochondrial Iron-Sulfur Cluster Activity and Cytosolic Iron Regulate Iron Traffic in Saccharomyces cerevisiae

“…Vacuoles from cells grown on iron-sufficient medium contain high concentrations of a NHHS Fe III complex in which the coordinating ligands are closely related to polyphosphate (6). A NHHS Fe II species evident in Mössbauer spectra of adenine-deficient whole cells may also be located in vacuoles (7). Under adeninesufficient conditions in which the vacuolar iron importer Ccc1 is either absent or overproduced, high levels of Fe II are present (6).…”

Ferric ions accumulate in the walls of metabolically inactivating Saccharomyces cerevisiae cells and are reductively mobilized during reactivation

“…Major spectral components were due to Fe II (BPS) 3 (48%), NHHS Fe III (24%), and two NHHS Fe II species (δ = 1.3 mm/s, ΔE Q = 3.0 mm/s, 10%; δ = 1.1 mm/s and ΔE Q = 3.8 mm/s, 16%; green and maroon lines, respectively, in Figure 9E). The latter two doublets arise from a lack of adenine in the medium (35). Under adenine-deficient conditions, ADE2 mutant strains such as the one used in this study turn pink and accumulate two types of NHHS Fe II species called Fe II ON and Fe II ONS .…”