Fernandes A R, Sá-Correia I
Centro de Engenharia Biológica e Química, Instituto Superior Técnico, 1049-001 Lisboa, Portugal.
Yeast. 2001 Apr;18(6):511-21. doi: 10.1002/yea.702.
For the adaptation of cells of Saccharomyces cerevisiae, a period of latency is necessary before exponential growth is resumed in a medium supplemented with a highly inhibitory concentration of copper. In this work, we have examined some physiological responses occurring during this period of adaptation. The results revealed that plasma membrane H(+)-ATPase (PM-ATPase) activity is strongly stimulated (up to 24-fold) during copper-induced latency in growth medium with glucose, reaching maximal levels when the cells were about to start inhibited exponential growth. This in vivo activation of the ATPase activity by copper was accompanied by the stimulation of the H(+)-pumping activity of the enzyme in vivo and was essentially due to the increase of the apparent V(max) for MgATP. Although the exact molecular basis of the reported plasma membrane ATPase activation was not clarified, no increase in the mRNA levels from the encoding genes PMA1 and PMA2 was apparently detected during copper-induced latency. The physiological response reported here may allow the cells to cope with copper-induced lipid peroxidation and consequent decrease in plasma membrane lipid ordering and increase in the non-specific permeability to protons. The consequences of these copper deleterious effects were revealed by the decrease of the intracellular pH (pH(i)) of the yeast population, from approximately pH(i) 6 to pH(i) 5, during copper-induced latency in growth medium at pH 4.3. The time-dependent patterns of plasma membrane ATPase activation and of the decrease of pH(i) during the period of adaptation to growth with copper correlate, suggesting that the regulation of this membrane enzyme activity may be triggered by intracellular acidification. Consistent with this idea, when exponential growth under copper stress was resumed and the pH(i) of the yeast population recovered up to physiological values, plasma membrane ATPase activity simultaneously decreased from the highly stimulated level attained during the adaptation period of latency.
对于酿酒酵母细胞的适应性而言，在添加了高抑制浓度铜的培养基中恢复指数生长之前，需要一段潜伏期。在这项工作中，我们研究了在此适应期内发生的一些生理反应。结果显示，在含有葡萄糖的生长培养基中，铜诱导潜伏期期间质膜H(+)-ATP酶（PM-ATP酶）活性受到强烈刺激（高达24倍），当细胞即将开始受到抑制的指数生长时达到最高水平。铜在体内对ATP酶活性的这种激活伴随着该酶在体内H(+)-泵浦活性的刺激，并且主要是由于MgATP的表观V(max)增加。尽管所报道的质膜ATP酶激活的确切分子基础尚未阐明，但在铜诱导的潜伏期内，未明显检测到编码基因PMA1和PMA2的mRNA水平增加。此处报道的生理反应可能使细胞能够应对铜诱导的脂质过氧化以及随之而来的质膜脂质有序性降低和质子非特异性通透性增加。在pH 4.3的生长培养基中，铜诱导潜伏期期间酵母群体的细胞内pH（pH(i)）从约pH(i) 6降至pH(i) 5，揭示了这些铜有害作用的后果。适应铜生长期间质膜ATP酶激活和pH(i)降低的时间依赖性模式相关，表明这种膜酶活性的调节可能由细胞内酸化触发。与此观点一致的是，当在铜胁迫下恢复指数生长且酵母群体的pH(i)恢复到生理值时，质膜ATP酶活性同时从潜伏期适应期达到的高度刺激水平下降。
