Graduate School of Integrated Arts and Sciences, Hiroshima University, 7-1, Kagamiyama 1-chome, Higashi-Hiroshima 739-8521, Japan.
Department of Chemistry, Faculty of Science, Saitama University, 255 Shimo-okubo, Sakura-ku, Saitama 338-8570, Japan.
Biochim Biophys Acta Biomembr. 2019 Feb 1;1861(2):441-448. doi: 10.1016/j.bbamem.2018.10.019. Epub 2018 Nov 8.
Mixed Langmuir films of type 1 alpha-(α-) and keto-mycolic acids (MAs) were investigated to understand the roles of α-methyl trans-cyclopropane containing keto-MA in determining the physical and chemical properties of the monolayers. Surface pressure (π) vs. mean molecular area (A) isotherms were measured at constant mole fractions defined as the ratio of the keto-MA molarity to the total molarity of α-MA and keto-MA (X) at 25 °C and 37 °C. A and the elastic modulus (E) of the mixed monolayer were compared for different X at fixed π values. In keto-MA rich monolayers, A values were much larger than values of the combined areas of α-MA and keto-MA, while the E values were close to those of solid keto-MA monolayers. A and E were also plotted against the mole fraction of α-methyl trans-cyclopropane containing keto-MA, which showed that the α-methyl trans-cyclopropane group stabilized the W-form conformation of mycolic acids in monolayers, and rendered them solid state. Furthermore, a comparison of the experimental results and the α-methyl trans-cyclopropane content in cell-wall MAs from various strains indicated that the ratio of trans-cyclopropane content was important in determining the nature of the mixed MA layer.
研究了 1 型α-（α-）和酮型酰基-mycolic 酸（MA）的混合 Langmuir 膜，以了解含α-甲基反式环丙烷的酮型 MA 在确定单层物理和化学性质中的作用。在 25°C 和 37°C 下，以定义为酮型 MA 摩尔浓度与α-MA 和酮型 MA 总摩尔浓度之比的恒定摩尔分数测量表面压力（π）与平均分子面积（A）等温线。在固定π值的情况下，比较了不同 X 时混合单层的 A 和弹性模量（E）。在富含酮型 MA 的单层中，A 值远大于α-MA 和酮型 MA 的组合面积值，而 E 值接近固体酮型 MA 单层的值。A 和 E 还与含α-甲基反式环丙烷的酮型 MA 的摩尔分数作图，表明α-甲基反式环丙烷基团稳定了单层中 mycolic acids 的 W 构象，并使其呈固态。此外，实验结果与来自不同菌株的细胞壁 MA 中的α-甲基反式环丙烷含量的比较表明，反式环丙烷含量的比值对于确定混合 MA 层的性质很重要。
