Department of Chemistry, Texas A&M University , College Station, Texas 77843-3255, United States.
Biochemistry. 2014 Jun 24;53(24):3940-51. doi: 10.1021/bi500148y. Epub 2014 Jun 11.
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) Fe(III) complexes with polyphosphate-related ligands. Some Fe(III) oxyhydroxide nanoparticles may also be present in these organelles, perhaps in equilibrium with the NHHS Fe(III). 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 Fe(III) citrate) accumulated two major NHHS Fe(II) species as the vacuolar NHHS Fe(III) 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 Fe(II) 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 Fe(III) with insignificant amounts of nanoparticles. The vacuoles of these cells might be more acidic than normal and can accommodate high concentrations of HS Fe(III) 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.
大多数富含铁的酵母细胞中的铁位于液泡中。这些酸性细胞器储存铁以备铁缺乏条件下使用，并将其与细胞的其他部分隔离，以避免与铁相关的毒性。液泡中的铁主要以一种或多种与多磷酸盐相关配体结合的磁分离非血红素高自旋（NHHS）Fe(III) 配合物的形式存在。这些细胞器中可能也存在一些 Fe(III) 氢氧化物纳米颗粒，也许与 NHHS Fe(III) 处于平衡状态。关于液泡中铁的化学性质知之甚少。当在腺嘌呤缺乏的培养基（A↓）上生长时，酵母 ADE2Δ 菌株（如 W303）会在腺嘌呤生物合成途径中产生一种有毒中间体。这种中间体与谷胱甘肽结合并被运送到液泡中解毒。通过穆斯堡尔和电子顺磁共振波谱法测定了 A↓ W303 细胞的铁含量。当它们从指数生长过渡到静止状态时，A↓ 细胞（补充 40 μM Fe(III) 柠檬酸盐）在液泡中积累了两种主要的 NHHS Fe(II) 物种，同时液泡中的 NHHS Fe(III) 物种减少。这表明 A↓ 细胞中的液泡比腺嘌呤充足的细胞更具还原性。尽管存在大量的 NHHS Fe(II) 配合物，但 A↓ 细胞受到的氧化应激较小；这种物质通常会促进芬顿化学。在含有额外酵母氮碱、氨基酸和碱基的最低培养基中生长 5 天的细胞中，大多数铁是 HS Fe(III)，只有少量纳米颗粒。这些细胞的液泡可能比正常情况下更酸，可以容纳高浓度的 HS Fe(III) 物种。葡萄糖水平和雷帕霉素（影响 TOR 系统）影响细胞铁含量。本研究说明了细胞铁对代谢、氧化还原状态和 pH 变化的敏感性。这些影响拓宽了我们对铁和整体细胞代谢如何整合的理解。
