Sousa M J, Miranda L, Côrte-Real M, Leão C
Department of Biology, University of Minho, Braga, Portugal.
Appl Environ Microbiol. 1996 Sep;62(9):3152-7. doi: 10.1128/aem.62.9.3152-3157.1996.
Cells of Zygosaccharomyces bailii ISA 1307 grown in a medium with acetic acid, ethanol, or glycerol as the sole carbon and energy source transported acetic acid by a saturable transport system. This system accepted propionic and formic acids but not lactic, sorbic, and benzoic acids. When the carbon source was glucose or fructose, the cells displayed activity of a mediated transport system specific for acetic acid, apparently not being able to recognize other monocarboxylic acids. In both types of cells, ethanol inhibited the transport of labelled acetic acid. The inhibition was noncompetitive, and the dependence of the maximum transport rate on the ethanol concentration was found to be exponential. These results reinforced the belief that, under the referenced growth conditions, the acid entered the cells mainly through a transporter protein. The simple diffusion of the undissociated acid appeared to contribute, with a relatively low weight, to the overall acid uptake. It was concluded that in Z. bailii, ethanol plays a protective role against the possible negative effects of acetic acid by inhibiting its transport and accumulation. Thus, the intracellular concentration of the acid could be maintained at levels lower than those expected if the acid entered the cells only by simple diffusion.
巴氏接合酵母ISA 1307的细胞在以乙酸、乙醇或甘油作为唯一碳源和能源的培养基中生长时，通过一个可饱和转运系统转运乙酸。该系统可接受丙酸和甲酸，但不接受乳酸、山梨酸和苯甲酸。当碳源为葡萄糖或果糖时，细胞表现出对乙酸具有特异性的介导转运系统的活性，显然无法识别其他一元羧酸。在这两种类型的细胞中，乙醇均抑制标记乙酸的转运。这种抑制是非竞争性的，并且发现最大转运速率对乙醇浓度的依赖性呈指数关系。这些结果强化了这样一种观点，即在所述生长条件下，酸主要通过转运蛋白进入细胞。未解离酸的简单扩散似乎对总酸摄取的贡献相对较小。得出的结论是，在巴氏接合酵母中，乙醇通过抑制乙酸的转运和积累，对乙酸可能产生的负面影响起到保护作用。因此，酸的细胞内浓度可以维持在低于仅通过简单扩散酸进入细胞时预期的水平。
