Costa V, Amorim M A, Reis E, Quintanilha A, Moradas-Ferreira P
Instituto de Ciências Biomédicas de Abel Salazar, Departamento de Biologia Molecular, e Centro de Citologia Experimental, Universidade do Porto, Portugal.
Microbiology (Reading). 1997 May;143 ( Pt 5):1649-1656. doi: 10.1099/00221287-143-5-1649.
This work reports the role of both superoxide dismutases-CuZnSOD (encoded by SOD1) and MnSOD (encoded by SOD2)-in the build-up of tolerance to ethanol during growth of Saccharomyces cerevisiae from exponential to post-diauxic phase. Both enzyme activities increase from the exponential phase to the diauxic shift and from the diauxic shift to the post-diauxic phase. The levels of mRNA-SOD1 and mRNA-SOD2 increase from the exponential phase to the diauxic shift; however, during the post-diauxic phase mRNA-SOD1 levels decrease while mRNA-SOD2 levels remain unchanged. These data indicate the existence of two regulatory mechanisms involved in the induction of SOD activity during growth: synthesis de novo of the proteins (until the diauxic shift), and post-transcriptional or post-translational regulation (during the post-diauxic phase). Ethanol does not alter the activities of either enzyme in cells from the diauxic shift or post-diauxic-phases, although the respective mRNA levels decrease in post-diauxic-phase cells treated with ethanol (14% or 20%). Results of experiments with sod1 and sod2 mutants show that MnSOD, but not CuZnSOD, is essential for ethanol tolerance of diauxic-shift and post-diauxic-phase cells. Evidence that ethanol toxicity is correlated with the production of reactive oxygen species in the mitochondria is obtained from results with respiration-deficient mutants. In these cells, the induction of superoxide dismutase activity by ethanol is low; also, the respiratory deficiency restores the capacity of sod2 cells to acquire ethanol tolerance.
本研究报道了超氧化物歧化酶——铜锌超氧化物歧化酶（由SOD1编码）和锰超氧化物歧化酶（由SOD2编码）在酿酒酵母从指数生长期到生长停滞后期对乙醇耐受性形成过程中的作用。两种酶的活性从指数生长期到生长停滞期转变以及从生长停滞期到生长停滞后期均有所增加。mRNA-SOD1和mRNA-SOD2的水平从指数生长期到生长停滞期转变时升高；然而，在生长停滞后期，mRNA-SOD1水平下降，而mRNA-SOD2水平保持不变。这些数据表明在生长过程中SOD活性诱导涉及两种调节机制：蛋白质的从头合成（直到生长停滞期转变）以及转录后或翻译后调节（在生长停滞后期）。乙醇不会改变处于生长停滞期转变或生长停滞后期的细胞中任何一种酶的活性，尽管在用乙醇处理（14%或20%）的生长停滞后期细胞中各自的mRNA水平会下降。对sod1和sod2突变体的实验结果表明，锰超氧化物歧化酶而非铜锌超氧化物歧化酶对于生长停滞期转变和生长停滞后期细胞的乙醇耐受性至关重要。从呼吸缺陷型突变体的结果中获得了乙醇毒性与线粒体中活性氧产生相关的证据。在这些细胞中，乙醇对超氧化物歧化酶活性的诱导作用较低；此外，呼吸缺陷恢复了sod2细胞获得乙醇耐受性的能力。
