A combination of three amino acids including 1.0 g/L isoleucine, 0.5 g/L methionine and 2.0 g/L phenylalanine was found to enhance ethanol tolerance of a self-flocculating fusant of Schizosaccharomyces pombe and Saccharomyces cerevisiae.When subjected to 20% (V/V) ethanol for 9 h at 30℃, all cells died whereas 57% remained viable for the cells grown in the presence of the three amino acids. Based on the analysis of protein amino acid composition of plasma membranes and the determination of plasma membrane fluidity by measuring fluorescence anisotropy using diphenylhexatriene as a probe, it was found that the significantly increased ethanol tolerance of cells grown with the three amino acids was due to the incorporation of the supplementary amino acids into the plasma membranes, thus resulting in enhanced ability of the plasma membranes to efficiently counteract the fluidizing effect of ethanol when subjected to ethanol stress. This is the first time to report that plasma membrane fluidity can be influenced by protein amino acid composition of plasma membranes.%实验显示,一种氨基酸混合液(含异亮氨酸、甲硫氨酸和苯丙氨酸,添加浓度分别为1.0、0.5和2.0g/L)能显著提高自絮凝酵母--粟酒裂殖酵母和酿酒酵母融合株SPSC的耐酒精能力.实验将菌体分别培养于添加(试验组)和未添加(对照组)该氨基酸混合液的条件下,然后收集菌体进行酒精(20%,V/V)冲击试验(30℃,9h),结果,试验组的菌体尚有一半以上的存活细胞,而对照组的菌体全部死亡.通过对试验组和对照组的菌体细胞膜蛋白质氨基酸组成分析发现,试验组的菌体耐酒精能力提高与所添加氨基酸组入菌体的细胞膜密切相关.以DPH为荧光探针的细胞膜流动性测定分析进一步揭示,氨基酸组入茵体的细胞膜后,细胞膜能有效抵抗高浓度酒精冲击诱发的膜流动性的提高,从而维持膜的稳定.因此,实验首次揭示膜蛋白氨基酸组成可通过改变膜流动性而影响酵母菌的耐酒精能力.
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