Premium
Excretion and uptake of cadaverine by CadB and its physiological functions in Escherichia coli
Author(s) -
Soksawatmaekhin Waraporn,
Kuraishi Aiko,
Sakata Kaori,
Kashiwagi Keiko,
Igarashi Kazuei
Publication year - 2004
Publication title -
molecular microbiology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.857
H-Index - 247
eISSN - 1365-2958
pISSN - 0950-382X
DOI - 10.1046/j.1365-2958.2003.03913.x
Subject(s) - cadaverine , putrescine , agmatine , antiporter , lysine decarboxylase , biochemistry , operon , biology , escherichia coli , spermidine , lysine , amino acid , enzyme , gene , membrane
Summary 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 µM 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.