Larsen P I, Sydnes L K, Landfald B, Strøm A R
Arch Microbiol. 1987 Feb;147(1):1-7. doi: 10.1007/BF00492896.
It has been shown previously that externally added glycine betaine is accumulated in Escherichia coli in response to the external osmotic strength. Here we have shown, by using nuclear magnetic resonance spectroscopy and radiochemical methods, that E. coli growing in a glucose-mineral medium of elevated osmotic strength generated with NaCl, had the same capacity to accumulate proline betaine and glycine betaine. Its capacity to accumulate gamma-butyrobetaine was, however, 40 to 50% lower. Accordingly, externally added proline betaine and glycine betaine stimulated aerobic growth of osmotically stressed cells equally well, and they were more osmoprotective than gamma-butyrobetaine. In cells grown at an osmotic strength of 0.64, 1.01, or 1.47 osmolal, respectively, the molal cytoplasmic concentration of the two former betaines corresponded to 29, 38, or 58% of the external osmotic strength. Nuclear magnetic resonance spectroscopy revealed that trehalose and glutamic acid were the only species of organic osmolytes accumulated in significant amounts in cells grown under osmotic stress in glucose-mineral medium without betaines. Their combined molal concentration in the cytoplasm of cells grown at 1.01 osmolal corresponded to 27% of the external osmotic strength.
先前的研究表明，外源添加的甘氨酸甜菜碱会在大肠杆菌中积累，以响应外部渗透压。在此我们通过核磁共振光谱法和放射化学方法表明，在由氯化钠产生的高渗透压葡萄糖 - 矿物质培养基中生长的大肠杆菌，积累脯氨酸甜菜碱和甘氨酸甜菜碱的能力相同。然而，其积累γ-丁酸甜菜碱的能力低40%至50%。因此，外源添加的脯氨酸甜菜碱和甘氨酸甜菜碱对渗透胁迫细胞的有氧生长刺激效果相同，并且它们的渗透保护作用比γ-丁酸甜菜碱更强。在分别于渗透压为0.64、1.01或1.47 osmolal的条件下生长的细胞中，前两种甜菜碱的摩尔细胞质浓度分别相当于外部渗透压的29%、38%或58%。核磁共振光谱显示，在不含甜菜碱的葡萄糖 - 矿物质培养基中，于渗透胁迫下生长的细胞中，海藻糖和谷氨酸是仅有的大量积累的有机渗透溶质种类。在渗透压为1.01 osmolal条件下生长的细胞的细胞质中，它们的摩尔浓度总和相当于外部渗透压的27%。
