Active Transport of Biotin in Escherichia coli K-12
Active Transport of Biotin in Escherichia coli K-12
复制标题
大肠杆菌 K-12 中生物素的主动转运
DOI：
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发表时间：
1974
影响因子：
3.2
通讯作者：
M. Eisenberg
中科院分区：
文献类型：
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作者：
O. Prakash;M. Eisenberg
研究了[14 C]生物素转运到生物素原养型大肠杆菌K-12菌株Y10-1细胞中的情况。该菌株细胞摄取的维生素主要以游离形式存在。加入葡萄糖可使吸收率提高6 - 8倍，在2 - 3 min内达到稳定水平，导致生物素逆浓度梯度积累。摄取显示出对温度（Q10，2.3;最适，37 ℃）和pH（最适6.6）的显著依赖性，并被碘乙酸抑制。葡萄糖依赖性摄取的活化能计算为16，200 cal/mol。随着生物素浓度的增加，生物素摄取速率显示出饱和动力学，表观Km和Vmax值分别为1.4 × 10−7 M和6.6 pmol/mg干细胞/min。在没有添加葡萄糖的情况下，细胞也积累生物素，尽管速度要低得多。这种积累更容易受到氧化磷酸化的叠氮化物和解偶联剂的抑制，这表明能量来源是通过电子传递链提供的。用许多生物素类似物进行的抑制研究表明需要完整的脲基环。在含生物素的培养基中生长的细胞中，生物素摄取被抑制，并且被证明是转运系统抑制的结果，表明生物素转运的控制。
The transport of [14C]biotin into cells of a biotin prototroph, Escherichia coli K-12 strain Y10-1, was investigated. The vitamin taken up by the cells in this strain existed primarily in the free form. Addition of glucose enhanced the rate of uptake six- to eightfold and the steady level was reached in 2 to 3 min resulting in accumulation of biotin against a concentration gradient. The uptake showed marked dependence on temperature (Q10, 2.3; optimum, 37 C) and pH (optimum 6.6) and was inhibited by iodoacetate. Energy of activation for glucose-dependent uptake was calculated to be 16,200 cal per mol. The rate of biotin uptake with increasing biotin concentrations showed saturation kinetics with an apparent Km and Vmax values of 1.4 × 10−7 M and 6.6 pmol per mg of dry cells per min respectively. The cells also accumulated biotin against a concentration gradient in the absence of added glucose, although at a much lower rate. This accumulation was much more susceptible to inhibition by azide and uncouplers of oxidative phosphorylation suggesting that the energy source was supplied through the electron-transport chain. Inhibition studies with a number of biotin analogues indicated the requirement for an intact ureido ring. The biotin uptake was inhibited in cells grown in biotin-containing medium and was shown to be the result of repression of the transport system, suggesting the control of the biotin transport.