Elliott B B, Mortenson L E
J Bacteriol. 1976 Aug;127(2):770-9. doi: 10.1128/jb.127.2.770-779.1976.
The regulation of the molybdate (MoO42-) transport activity of Clostridium pasteurianum has been studied by observing the effects of NH3, carbamyl phosphate, MoO42-, and chloramphenicol on the ability of cells to take up MoO42-. Compared with cells fixing N2, cells grown in the presence of 1 mM NH3 are greater than 95% repressed for MoO42- transport. Uptake activity begins to increase just before NH exhaustion (under Ar or N2) and continues to increase throughout the lag period as cells shift from NH3-growing to N2-fixing conditions. When cells are shifted from N2-fixing to NH3-growing conditions the transport activity per fixed number of cells decreases by increase of bells in absence of transport synthesis. Carbamyl phosphate (greater than or equal to 15 mM) but not NH3 inhibits 58% of the in vitro uptake activity. When 1 mM carbamyl phosphate is added just before the exhaustion of NH3, the transport activity, measured 2 h later, is 100% repressed. Cells grown in the presence of high MoO42- (1mM) are 80% repressed for MoO42- transport. Synthesis of the MoO42- transport system is also completely stopped when chloramphenicol (300 mug/ml) is added just before the exhaustion oNH 3 from the medium. These findings demonstrate that the ability of cells to transport MoO42- is dependent upon new protein synthesis and can be repressed by high levels of substrate. The regulation of MoO42- uptake by NH3 or carbamyl phosphate closely parallels the regulation of nitrogenase activity. Activity of neither nitrogenase component (Fe protein or MoFe protein) was detected even 3 h after the exhaustion of the NH3 if either MoO42- was absent or if WO42- was present in place of MoO42-. The duration of the diauxic lag increases with decreasing concentration of MoO42- in the medium. If no MoO42- is present the lag continues indefinitely. If MoO42- is added late in the lag period, growth under N2-fixing conditions resumes but only after a normal induction period.
通过观察氨、氨基甲酰磷酸、钼酸根离子（MoO42-）和氯霉素对巴氏梭菌吸收MoO42-能力的影响，研究了该菌钼酸根离子（MoO42-）转运活性的调节机制。与固氮细胞相比，在1 mM氨存在下生长的细胞，其MoO42-转运能力受到95%以上的抑制。在氨耗尽前（在氩气或氮气环境下），摄取活性开始增加，并在整个延迟期持续增加，此时细胞从以氨为氮源的生长状态转变为固氮状态。当细胞从固氮状态转变为以氨为氮源的生长状态时，在没有转运合成增加的情况下，每固定数量细胞的转运活性会因细胞数量增加而降低。氨基甲酰磷酸（大于或等于15 mM）而非氨会抑制58%的体外摄取活性。当在氨耗尽前加入1 mM氨基甲酰磷酸时，2小时后测得的转运活性被完全抑制。在高浓度MoO42-（1 mM）存在下生长的细胞，其MoO42-转运能力被抑制80%。当在培养基中氨耗尽前加入氯霉素（300 μg/ml）时，MoO42-转运系统的合成也会完全停止。这些发现表明，细胞转运MoO42-的能力依赖于新蛋白质的合成，并且会被高水平的底物抑制。氨或氨基甲酰磷酸对MoO42-摄取的调节与固氮酶活性的调节密切平行。如果不存在MoO42-或用WO42-代替MoO42-，即使在氨耗尽3小时后，也检测不到固氮酶组分（铁蛋白或钼铁蛋白）的活性。双相生长延迟期的持续时间随着培养基中MoO42-浓度的降低而增加。如果不存在MoO42-，延迟期将无限持续。如果在延迟期后期加入MoO42-，固氮条件下的生长将恢复，但仅在经过正常诱导期之后。
