Kadner R J, Bassford P J
J Bacteriol. 1977 Jan;129(1):254-64. doi: 10.1128/jb.129.1.254-264.1977.
The uptake of vitamin B12 was measured in cells of Escherichia coli whose growth had been inhibited by any of a variety of treatments. In all cases, the secondary, energy-dependent phase of B12 uptake was depressed in proportion to the decrease in growth rate, but uptake was constant in cells growing logarithmically at different rates. The depression of B12 uptake activity was independent of the site of cell metabolism affected by the inhibitor or by its effect on cell viability, and was both more rapid and of greater degree than the effects on the uptake of any of the six amino acids tested. The decline was not affected by inhibitors of either cell division or proteolysis and was manifested without any apparent decrease in the surface B12 binding activity. Transport activity was rapidly regained upon reversal of the inhibition of protein synthesis. Prompted by this response, the uptake of B12 was contrasted to the apparent uptake of the E colicins, which share the same outer membrane receptor. Sensitivity to colicin E1, measured by its inhibition of proline uptake, was not affected by growth inhibition by antibiotic treatment. Finally, there was no specific depression of B12 uptake in cells rendered colicin tolerant either by mutation or as a consequence of phage f1 infection.
在经多种处理抑制生长的大肠杆菌细胞中测量维生素B12的摄取。在所有情况下，B12摄取的次级能量依赖阶段与生长速率的降低成比例地降低，但在以不同速率对数生长的细胞中摄取是恒定的。B12摄取活性的降低与抑制剂影响的细胞代谢位点或其对细胞活力的影响无关，并且比其对所测试的六种氨基酸中任何一种的摄取的影响更快且程度更大。这种下降不受细胞分裂或蛋白水解抑制剂的影响，并且在表面B12结合活性没有任何明显降低的情况下表现出来。在蛋白质合成抑制被逆转后，转运活性迅速恢复。受这种反应的启发，将B12的摄取与大肠杆菌素的明显摄取进行了对比，大肠杆菌素共享相同的外膜受体。通过其对脯氨酸摄取的抑制来测量的对大肠杆菌素E1的敏感性不受抗生素处理抑制生长的影响。最后，无论是通过突变还是由于噬菌体f1感染而使细胞对大肠杆菌素耐受，B12摄取都没有特异性降低。
