Camarasa Carole, Faucet Virginie, Dequin Sylvie
UMR1083 Sciences pour l'Oenologie, INRA, 2 Place Viala, F-34060 Montpellier, France.
Yeast. 2007 May;24(5):391-401. doi: 10.1002/yea.1467.
Saccharomyces cerevisiae possesses both a cytoplasmic and a mitochondrial fumarate reductase, encoded by FRDS1 and OSM1, respectively. While previous studies have shown that mutants lacking FRDS1 and OSM1 cannot grow under anaerobiosis (Arikawa et al., 1998), the physiological role of fumarate reductase (FR) remains poorly understood. Here, we report that an osm1 frds1 mutant is unable to grow anaerobically, even with glutamate as a sole nitrogen source, when succinate can be produced by the TCA oxidative branch. We also show that the growth of the mutant is not restored by adding acetoin, an alternative sink for NADH oxidation, but it is at least partly restored by the addition of oxygen or menadione, which can oxidize FADH(2) in addition to NADH. These data indicate that the growth inhibition of the mutant is due to an inability to reoxidize FAD, rather than an indirect effect on NADH or an inability to produce succinate per se. During anaerobic growth, FRDS1 expression was two to eight times higher than that of OSM1, and fumarate reductase activity was higher in the osm1 mutant than in the frds1 mutant. FRDS1 expression was induced by anaerobiosis, and this induction was abolished in a rox1 mutant. We conclude that the formation of succinate is strictly required for the reoxidation of FADH(2) during anaerobiosis, and that it is regulated through the control of FRDS1 expression when oxygen is limiting. Based on these data, we discuss the potential role of fumarate reductase in the regeneration of the FAD-prosthetic group of essential flavoproteins.
酿酒酵母拥有细胞质和线粒体富马酸还原酶，分别由FRDS1和OSM1编码。虽然先前的研究表明，缺乏FRDS1和OSM1的突变体在厌氧条件下无法生长（有川等人，1998年），但富马酸还原酶（FR）的生理作用仍知之甚少。在此，我们报告，当三羧酸循环氧化分支可以产生琥珀酸时，即使以谷氨酸作为唯一氮源，osm1 frds1突变体在厌氧条件下也无法生长。我们还表明，添加乙偶姻（NADH氧化的替代汇）不能恢复突变体的生长，但添加氧气或甲萘醌至少可以部分恢复其生长，甲萘醌除了可以氧化NADH外，还可以氧化FADH₂。这些数据表明，突变体的生长抑制是由于无法重新氧化FAD，而不是对NADH的间接影响或无法产生琥珀酸本身。在厌氧生长期间，FRDS1的表达比OSM1高两到八倍，并且osm1突变体中的富马酸还原酶活性高于frds1突变体。FRDS1的表达由厌氧诱导，并且在rox1突变体中这种诱导被消除。我们得出结论，在厌氧期间，琥珀酸的形成对于FADH₂的重新氧化是严格必需的，并且当氧气有限时，它通过FRDS1表达的控制来调节。基于这些数据，我们讨论了富马酸还原酶在必需黄素蛋白的FAD辅基再生中的潜在作用。
