Coote P J, Jones M V, Seymour I J, Rowe D L, Ferdinando D P, McArthur A J, Cole M B
Microbiology Section, Unilever Research, Colworth Laboratory, Sharnbrook, Bedford, UK.
Microbiology (Reading). 1994 Aug;140 ( Pt 8):1881-90. doi: 10.1099/13500872-140-8-1881.
The role of membrane integrity and the membrane ATPase in the mechanism of thermotolerance in Saccharomyces cerevisiae was investigated. The resistance to lethal heat of a mutant strain with reduced expression of the membrane ATPase was significantly less than that of the wild-type parent. However, prior exposure to sub-lethal temperatures resulted in the induction of similar levels of thermotolerance in the mutant compared to the parent strain, suggesting that the mechanism of sub-lethal heat-induced thermotolerance is independent of ATPase activity. Supporting this, exposure to sub-lethal heat stress did not result in increased levels of glucose-induced acid efflux at lethal temperatures and there was little correlation between levels of acid efflux and levels of heat resistance. ATPase activity in crude membrane preparations from sub-lethally heat-stressed cells was similar to that in preparations from unstressed cells. Study of net acid flux during heating revealed that pre-stressed cells were able to protect the proton gradient for longer. This may confer an 'advantage' to these cells that results in increased thermotolerance. This was supported by the observation that prior exposure to sub-lethal heat resulted in a transient protection against the large increase in membrane permeability that occurs at lethal temperatures. However, no protection against the large drop in intracellular pH was detected. Sub-lethal heat-induced protection of membrane integrity also occurred to the same extent in the reduced-expression membrane ATPase mutant, further implying that the mechanism of induced thermotolerance is independent of ATPase activity. To conclude, although the membrane ATPase is essential for basal heat resistance, thermotolerance induced by prior exposure to stress is largely conferred by a mechanism that is independent of the enzyme.
研究了膜完整性和膜ATP酶在酿酒酵母耐热机制中的作用。膜ATP酶表达降低的突变菌株对致死热的抗性明显低于野生型亲本。然而，与亲本菌株相比，预先暴露于亚致死温度会导致突变体中诱导出相似水平的耐热性，这表明亚致死热诱导的耐热机制与ATP酶活性无关。支持这一点的是，暴露于亚致死热应激不会导致在致死温度下葡萄糖诱导的酸外排水平增加，并且酸外排水平与耐热水平之间几乎没有相关性。来自亚致死热应激细胞的粗膜制剂中的ATP酶活性与未应激细胞制剂中的相似。加热过程中净酸通量的研究表明，预先应激的细胞能够更长时间地保护质子梯度。这可能赋予这些细胞一种“优势”，从而导致耐热性增加。预先暴露于亚致死热会导致对致死温度下发生的膜通透性大幅增加产生短暂保护，这一观察结果支持了这一点。然而，未检测到对细胞内pH大幅下降的保护作用。在膜ATP酶表达降低的突变体中，亚致死热诱导的膜完整性保护也在相同程度上发生，这进一步表明诱导耐热性的机制与ATP酶活性无关。总之，虽然膜ATP酶对于基础耐热性至关重要，但预先暴露于应激诱导的耐热性很大程度上是由一种独立于该酶的机制赋予的。
