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Inducer exclusion in Escherichia coli by non‐PTS substrates: the role of the PEP to pyruvate ratio in determining the phosphorylation state of enzyme IIA Glc
Author(s) -
Hogema Boris M.,
Arents Jos C.,
Bader Rechien,
Eijkemans Kevin,
Yoshida Hiromi,
Takahashi Hideyuki,
Aiba Hiroji,
Postma Pieter W.
Publication year - 1998
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.1365-2958.1998.01053.x
Subject(s) - dephosphorylation , catabolite repression , pep group translocation , biochemistry , biology , phosphorylation , phosphoenolpyruvate carboxykinase , enzyme , phosphotransferase , escherichia coli , inducer , phosphatase , mutant , gene
The main mechanism causing catabolite repression in Escherichia coli is the dephosphorylation of enzyme IIA Glc , one of the enzymes of the phosphoenolpyruvate:carbohydrate phosphotransferase system (PTS). The PTS is involved in the uptake of a large number of carbohydrates that are phosphorylated during transport, phosphoenolpyruvate (PEP) being the phosphoryl donor. Dephosphorylation of enzyme IIA Glc causes inhibition of uptake of a number of non‐PTS carbon sources, a process called inducer exclusion. In this paper, we show that dephosphorylation of enzyme IIA Glc is not only caused by the transport of PTS carbohydrates, as has always been thought, and that an additional mechanism causing dephosphorylation exists. Direct monitoring of the phosphorylation state of enzyme IIA Glc also showed that many carbohydrates that are not transported by the PTS caused dephosphorylation during growth. In the case of glucose 6‐phosphate, it was shown that transport and the first metabolic step are not involved in the dephosphorylation of enzyme IIA Glc , but that later steps in the glycolysis are essential. Evidence is provided that the [PEP]–[pyruvate] ratio, the driving force for the phosphorylation of the PTS proteins, determines the phosphorylation state of enzyme IIA Glc . The implications of these new findings for our view on catabolite repression and inducer exclusion are discussed.