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The transport of PTS-sugars other than glucose can affect the phosphorylation of Enzyme IIA^Glc simply by generating competition for phosphorylation between the phosphotransfer proteins.  Such competition indirectly regulates adenylate cyclase activity.

This type of regulation has been proposed by Crasnier-Mednansky et al. in 1997 [Microbiology].  It occurs when enhanced transport of the PTS-sugar fructose takes place.

The sequential transfer of phosphate from PEP to fructose does not involve, unlike other PTS, HPr but the diphosphoryl transfer protein, FruB [Medline] which was renamed Enzyme IIAMH^Fru.

In fruR mutant strains lacking the fructose repressor FruR (also called Cra), Enzyme IIA^Glc is largely unphosphorylated when cells are grown in fructose-containing medium.  In such conditions the fructose operon (fruBKA) is over-expressed thus leading to competition for phosphorylation between Enzyme IIAMH^Fru (FruB) and HPr.

Because of the competition between the phosphoproteins, phosphorylation of Enzyme IIA^Glc is impaired; as a consequence adenylate cyclase becomes 'inactive' (in idle mode).  Therefore fruR mutant strains grown on fructose exhibit cAMP levels that are much lower than those in wild-type strains grown on fructose.  With carbon sources other than fructose, cAMP levels of fruR and wild-type strains are comparable [Microbiology]¹.  One of the physiological consequences of Enzyme IIA^Glc unphosphorylation is that fructose can substitute for glucose in producing diauxie but only in fruR strains² [MIeJ].

Competition for phosphorylation between PTS constituents seems to be a crucial determinant of adenylate cyclase regulation, as exemplified by the study of fruR mutant strains.

Competition for phosphorylation is also likely to occur when transport of several PTS-sugars takes place.  Limited phosphoryl flux may be a constituent of the winner-take-all behavior, as revealed by theoretical studies of metabolic switching in the PTS [Biophys J].

In the case of a non-PTS carbon source, for example glucose-6-phosphate, the regulation of adenylate cyclase activity is more difficult to apprehend, as glucose-6-phosphate transport or metabolism is not known to involve PTS proteins, especially Enzyme IIA^Glc.

Footnotes:

¹ In the 2007 J Bacteriol article "Correlation between growth rates, EIIA phosphorylation, and intracellular cAMP levels in Escherichia coli K-12" Bettenbrock et al. improperly reported, by referring to the 1997 Microbiology article, that lack of HPr enhances cAMP production in fructose-grown E. coli.  Generally lack of HPr results in a low production of cAMP!

²E. coli wild-type strains exhibit diauxic growth with glucose or mannitol as the "preferred" carbon source but not with fructose [Jacques Monod, Ph.D. thesis, 1942] [Microbiol Mol Biol Rev].

To Chapter IV: Glucose 6-phosphate transport