Choline transport activity in Staphylococcus aureus induced by osmotic stress and low phosphate concentrations.
Choline transport activity in Staphylococcus aureus induced by osmotic stress and low phosphate concentrations.
复制标题
渗透胁迫和低磷酸盐浓度诱导金黄色葡萄球菌中的胆碱转运活性。
DOI：
10.1128/jb.175.8.2400-2406.1993
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发表时间：
1993
影响因子：
3.2
通讯作者：
Wilkinson,BJ
中科院分区：
文献类型：
--
作者：
Kaenjak,A;Graham,JE;Wilkinson,BJ
延迟2.5~3.5h后，金黄色葡萄球菌对指数相金黄色葡萄球菌的高渗胁迫开始摄取~(14)C胆碱，氯霉素可阻止这种摄取，提示这种摄取是通过诱导转运系统发生的。来自[14C]胆碱的放射性以[14C]甘氨酸甜菜碱的形式累积。然而，胆碱和甘氨酸甜菜碱都不能作为生物体的主要碳源和能量来源，这表明胆碱的代谢不超过甘氨酸甜菜碱。对不同培养条件下培养的细胞胆碱转运活性的测定表明，渗透胁迫是诱导的主要原因，而胆碱的诱导作用进一步增强。该系统在厌氧培养的细胞中不被诱导。甘氨酸甜菜碱和脯氨酸甜菜碱抑制胆碱转运活性，提示这些化合物是辅阻遏物。1M磷酸二氢钾或0.5M磷酸二氢钠在渗透胁迫下不能诱导细胞胆碱转运活性，但在无渗透应激的低磷培养细胞中可诱导胆碱转运活性。这表明，磷酸盐和渗透胁迫调节之间存在联系。胆碱转运依赖于能量和Na+，Km为46微米，最大转运速率(Vmax)为54nmol/min/mg(干重)。竞争研究的结果表明，N-甲基和分子末端的醇基或醛基团在其被系统识别中起着重要的作用。甘氨酸甜菜碱不是一个高效的竞争者，这表明它的运输系统和胆碱运输系统是不同的。胆碱转运对多种抑制剂高度敏感，这可能与在高浓度NaCI存在下生长的细胞对呼吸代谢的依赖程度更高有关。
Uptake of [14C]choline upon hyperosmotic stress of exponential-phase Staphylococcus aureus cultures in a complex medium occurred after a delay of 2.5 to 3.5 h. This uptake could be prevented by chloramphenicol, suggesting that it occurred via an inducible transport system. Radioactivity from [14C]choline was accumulated as [14C]glycine betaine. However, neither choline nor glycine betaine could act as the major carbon and energy source for the organism, suggesting that choline was not metabolized beyond glycine betaine. Assay of choline transport activity in cells grown under different conditions in defined media revealed that osmotic stress was mainly responsible for the induction, but choline gave a further increase in induction. The system was not induced in anaerobically grown cells. Choline transport activity was repressed by glycine betaine and proline betaine, suggesting that these compounds are corepressors. Choline transport activity was not induced in cells osmotically stressed by 1 M potassium phosphate or 0.5 M sodium phosphate, but was induced in cells grown in low-phosphate medium in the absence of osmotic stress. This suggests that there is a connection between the phosphate and osmotic stress regulons. Choline transport was energy and Na+ dependent and had a Km of 46 microM and a maximum rate of transport (Vmax) of 54 nmol/min/mg (dry weight). The results of competition studies suggested that N-methyl and an alcohol group or aldehyde groups at the ends of the molecule were important in its recognition by the system. Glycine betaine was not a highly effective competitor, suggesting that its transport system and the choline transport system were distinct from each other. Choline transport was highly susceptible to a variety of inhibitors, which may be related to the greater dependence on respiratory metabolism of cells grown in the presence of high NaC1 concentrations.