Evidence for the presence of a second electron donor for the cytoplasmic thioredowins in the yeast Saccharomyces cerevisiae

Maya mantarında sitoplazmik tioredoksin sistemi NADPH, bir tane tiyoredoksin redüktaz (TRR1) ve iki tane tiyoredoksin (TRX1, TRXZ) den oluşmaktadır. Bu çalışmada, genomundan TRR1, TRXl.ve TRXZ genleri çıkartılmış maya hücrelerinin metiyonin sülfoksit indirgeme kapasiteleri incelenmiştir. İki tiyoredoksini aynı anda çıkartılmış mutant hücreler metiyonin sulfoksiti indirgeyip metiyonin oluşturamazken, tiyoredoksin redüktaz-1 geni çıkartılmış hücreler oluşturabildiler. Bu maya mantarında metiyonin sülfoksit redüktazlar için gerekli olan elektronların tiyoredoksinlerden sağlandığını gösteren ilk çalışmadır. Ayrıca metiyonin sülfoksit indirgenmesi için gerekli olan elektronlar tiyoredoksin redüktaz-1 olmadan NADPH den tiyoredoksine transfer edilebildiler. Aynı sonuç sülfatın indirgenip methiyonin sentezinde kullanılmasında rol oynayan 3-fosfoadenozin 5-fosfosülfat redüktaz enzim aktivitesi içinde gözlemlendi. Her iki deneyin sonuçlarına göre, tiyoredoksin redüktaz-1 in yokluğunda tiyoredoksinler için gerekli olan elektronlar kimliği bilinmeyen ikinci bir elektron donörü tarafından sağlanmaktadır.

Maya (Saccharomyces cerevisiae) Sitoplazmik tiyoredoksinler iiçin ikinci bir elektron donörününvarlığını göjsteren delilller

In yeast, the cytoplasmic thioredoxin system is composed of NADPH, thioredoxin reductase-1 {TRR1) and 2 thioredoxin genes (TRX1, TRXZ). In this study, using yeast knockout mutants for TRR1, TRX1 and TRX2 genes, the role of the thioredoxin system in methionine sulfoxide reduction was investigated. Cells lacking both TRX1 and TRXZ genes simultaneously were not able to reduce methionine sulfoxides to methionine; however, mutants missing the TRR1 gene were able to reduce methionine sulfoxides to methionine, which showed that electrons could be transferred from NADPH to thioredoxins in the absence of TRR1. Similar results were observed for 3-phosphoadenosine 5-phosphosulfate reduction in the inorganic sulfate assimilation pathway. Results from both assays suggested that yeast cells have additional cytoplasmic thioredoxin reductase activity that could compensate for methionine sulfoxide reduction and sulfate assimilation in the absence of TRR1. This report also constitutes the first evidence that thioredoxins are the in vivo electron donors for methionine sulfoxide reductases in yeast.

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