Prakash O, Eisenberg M A
J Bacteriol. 1974 Nov;120(2):785-91. doi: 10.1128/jb.120.2.785-791.1974.
The transport of [(14)C]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 (Q(10), 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 K(m) and V(max) values of 1.4 x 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.
对生物素原养型大肠杆菌K-12菌株Y10-1细胞摄取[(14)C]生物素的过程进行了研究。该菌株细胞摄取的维生素主要以游离形式存在。添加葡萄糖可使摄取速率提高6至8倍，并在2至3分钟内达到稳定水平，从而使生物素逆浓度梯度积累。摄取过程对温度（Q(10)为2.3；最适温度为37℃）和pH（最适pH为6.6）有明显依赖性，并受到碘乙酸的抑制。计算得出葡萄糖依赖性摄取的活化能为每摩尔16,200卡。随着生物素浓度增加，生物素摄取速率呈现饱和动力学，表观K(m)和V(max)值分别为1.4×10(-7)M和每分钟每毫克干细胞6.6皮摩尔。在不添加葡萄糖的情况下，细胞也能使生物素逆浓度梯度积累，不过速率要低得多。这种积累对叠氮化物和氧化磷酸化解偶联剂的抑制更为敏感，这表明能量来源是通过电子传递链提供的。对多种生物素类似物的抑制研究表明，需要完整的脲基环。在含生物素培养基中生长的细胞中，生物素摄取受到抑制，这表明是转运系统受到阻遏的结果，提示生物素转运存在调控。
