Perroud B, Le Rudulier D
J Bacteriol. 1985 Jan;161(1):393-401. doi: 10.1128/jb.161.1.393-401.1985.
Exogenous glycine betaine highly stimulates the growth rate of various members of the Enterobacteriaceae, including Escherichia coli, in media with high salt concentrations (D. Le Rudulier and L. Bouillard, Appl. Environ. Microbiol. 46:152-159, 1983). In a nitrogen- and carbon-free medium, glycine betaine did not support the growth of E. coli either on low-salt or high-salt media. This molecule was taken up by the cells but was not catabolized. High levels of glycine betaine transport occurred when the cells were grown in media of elevated osmotic strength, whereas relatively low activity was found when the cells were grown in minimal medium. A variety of electrolytes, such as NaCl, KCl, NaH2PO4, K2HPO4, K2SO4, and nonelectrolytes like sucrose, raffinose, and inositol triggered the uptake of glycine betaine. Furthermore, in cells subjected to a sudden osmotic upshock, glycine betaine uptake showed a sixfold stimulation 30 min after the addition of NaCl. Part of this stimulation might be a consequence of protein synthesis. The transport of glycine betaine was energy dependent and occurred against a concentration gradient. 2,4-Dinitrophenol almost totally abolished the glycine betaine uptake. Azide and arsenate exerted only a small inhibition. In addition, N,N'-dicyclohexylcarbodiimide had a very low inhibitory effect at 1 mM. These results indicated that glycine betaine transport is driven by the electrochemical proton gradient. The kinetics of glycine betaine entry followed the Michaelis-Menten relationship, yielding a Km of 35 microM and a Vmax of 42 nmol min-1 mg of protein-1. Glycine betaine transport showed considerable structural specificity. The only potent competitor was proline betaine when added to the assay mixtures at 20-fold the glycine betaine concentration. From these results, it is proposed that E. coli possesses an active and specific glycine betaine transport system which is regulated by the osmotic strength of the growth medium.
外源甘氨酸甜菜碱能在高盐浓度培养基中极大地刺激肠杆菌科各成员（包括大肠杆菌）的生长速率（D.勒鲁迪利耶和L.布亚尔，《应用与环境微生物学》46:152 - 159，1983年）。在无氮无碳培养基中，无论在低盐还是高盐培养基上，甘氨酸甜菜碱都不能支持大肠杆菌生长。该分子能被细胞摄取，但不会被分解代谢。当细胞在渗透压升高的培养基中生长时，会发生高水平的甘氨酸甜菜碱转运，而当细胞在基本培养基中生长时，转运活性相对较低。多种电解质，如氯化钠、氯化钾、磷酸二氢钠、磷酸氢二钾、硫酸钾，以及非电解质如蔗糖、棉子糖和肌醇，都会引发甘氨酸甜菜碱的摄取。此外，在受到突然渗透压升高冲击的细胞中，添加氯化钠30分钟后，甘氨酸甜菜碱摄取显示出六倍的刺激。这种刺激的一部分可能是蛋白质合成的结果。甘氨酸甜菜碱的转运依赖能量且是逆浓度梯度进行的。2,4 - 二硝基苯酚几乎完全消除了甘氨酸甜菜碱的摄取。叠氮化物和砷酸盐仅产生轻微抑制作用。此外，N,N'-二环己基碳二亚胺在1 mM时抑制作用非常低。这些结果表明甘氨酸甜菜碱转运是由电化学质子梯度驱动的。甘氨酸甜菜碱进入细胞的动力学遵循米氏关系，米氏常数Km为35 μM，最大反应速度Vmax为42 nmol·min⁻¹·mg蛋白质⁻¹。甘氨酸甜菜碱转运表现出相当程度的结构特异性。当以甘氨酸甜菜碱浓度20倍的量添加到测定混合物中时，唯一有效的竞争者是脯氨酸甜菜碱。根据这些结果，推测大肠杆菌拥有一个由生长培养基渗透压调节的活跃且特异性的甘氨酸甜菜碱转运系统。
