Soksawatmaekhin Waraporn, Kuraishi Aiko, Sakata Kaori, Kashiwagi Keiko, Igarashi Kazuei
Graduate School of Pharmaceutical Sciences, Chiba University, 1-33 Yayoi-cho, Inage-ku, Chiba 263-8522, Japan.
Mol Microbiol. 2004 Mar;51(5):1401-12. doi: 10.1046/j.1365-2958.2003.03913.x.
The functions of the putative cadaverine transport protein CadB were studied in Escherichia coli. CadB had both cadaverine uptake activity, dependent on proton motive force, and cadaverine excretion activity, acting as a cadaverine-lysine antiporter. The Km values for uptake and excretion of cadaverine were 20.8 and 303 microM respectively. Both cadaverine uptake and cadaverine-lysine antiporter activities of CadB were functional in cells. Cell growth of a polyamine-requiring mutant was stimulated slightly at neutral pH by the cadaverine uptake activity and greatly at acidic pH by the cadaverine-lysine antiporter activity. At acidic pH, the operon containing cadB and cadA, encoding lysine decarboxylase, was induced in the presence of lysine. This caused neutralization of the extracellular medium and made possible the production of CO(2) and cadaverine and aminopropylcadaverine instead of putrescine and spermidine. The induction of the cadBA operon also generated a proton motive force. When the cadBA operon was not induced, the expression of the speF-potE operon, encoding inducible ornithine decarboxylase and a putrescine-ornithine antiporter, was increased. The results indicate that the cadBA operon plays important roles in cellular regulation at acidic pH.
在大肠杆菌中研究了假定的尸胺转运蛋白CadB的功能。CadB既具有依赖质子动力的尸胺摄取活性，又具有作为尸胺 - 赖氨酸反向转运体的尸胺排泄活性。尸胺摄取和排泄的Km值分别为20.8和303微摩尔。CadB的尸胺摄取和尸胺 - 赖氨酸反向转运体活性在细胞中均有功能。在中性pH下，多胺需求突变体的细胞生长因尸胺摄取活性而略有刺激，在酸性pH下则因尸胺 - 赖氨酸反向转运体活性而受到极大刺激。在酸性pH下，在赖氨酸存在的情况下，含有cadB和编码赖氨酸脱羧酶的cadA的操纵子被诱导。这导致细胞外培养基中和，并使得产生二氧化碳、尸胺和氨丙基尸胺而非腐胺和亚精胺成为可能。cadBA操纵子的诱导也产生了质子动力。当cadBA操纵子未被诱导时，编码诱导型鸟氨酸脱羧酶和腐胺 - 鸟氨酸反向转运体的speF - potE操纵子的表达增加。结果表明，cadBA操纵子在酸性pH下的细胞调节中起重要作用。
