Note: a dashed line (without arrowheads) between two compound names is meant to imply that the two names are just different instantiations of the same compound -- i.e. one may be a specific name and the other a general name, or they may both represent the same compound in different stages of a polymerization-type pathway. If an enzyme name is shown in bold, there is experimental evidence for this enzymatic activity.
Locations of Mapped Genes:
|Superclasses:||Degradation/Utilization/Assimilation → Carbohydrates Degradation → Sugars Degradation|
It is well known that Escherichia coli can use glucose as a sole source of carbon and energy. The D isomer of glucose is widely found in nature and the β-D-glucose anomer is predominant in aqueous solution [Franks87]. Exogenous β-D-glucose enters the cell through outer membrane porins and is then actively transported into the cell via the inner membrane phosphotransferase system (PTS) which transforms it into β-D-glucose-6-phosphate as it crosses the cell membrane. β-D-glucose-6-phosphate is also produced biosynthetically during gluconeogenesis. β-D-glucose-6-phosphate is one of the basic precursor metabolites for biosynthetic pathways. It is also a substrate for the central degradative pathways glycolysis and the pentose phosphate cycle.
E. coli can also grow on exogenously supplied glucose-1-phosphate (minimal medium containing glucose 1-phosphate) as sole carbon source [Pradel91]. Endogenous α-D-glucose-1-phosphate is an intermediate in the metabolism of glycogen and galactose. It is a building block for the sugar nucleotide UDP-glucose, which is used in some biosynthetic pathways. Reviewed by Mayer, C. and W. Boos in [ECOSAL] (see below).
About This Pathway
The dashed line connecting D-glucose with β-D-glucose is meant to show that the pathway is possible, but incompletely defined. The anomeric form (α or β) of the D-glucose product of EC 184.108.40.206 is not specified by the EC and it was not found in the literature for the indicated phosphatases. However, if α-D-glucose is produced, it may either spontaneously convert to β-D-glucose, or E. coli aldose-1-epimerase (mutarotase, EC 220.127.116.11) could convert it to β-D-glucose [Bouffard94] and in [Mulhern73].
Substrates β-D-glucose and α-D-glucose-1-phosphate may be derived from exogenous sources, or endogenously produced, as indicated by the input pathway links. In general, the ability to utilize sugars and their modes of utilization are strain-dependent in Escherichia coli.
Exogenous β-D-glucose uptake via the PTS curbs the utilization of other exogenous sugars, which is known as the glucose effect. This effect is lost if β-D-glucose becomes limiting. Under these conditions β-D-glucose can also enter the cell without phosphorylation, via outer membrane porins and the Mgl ABC transporter (not shown).
Endogenous β-D-glucose can be produced by pathways for the degradation of glucose-containing disaccharides such as maltose (see pathway glycogen degradation I (bacterial)) trehalose, lactose and melibiose, as shown in the pathway links. In contrast to exogenous β-D-glucose which is phosphorylated by the PTS, endogenous β-D-glucose is phosphorylated by glucokinase before entering central metabolism, as shown in the pathway links (in [Meyer97]). More recently, a role for glucokinase and glucose in a complex regulatory mechanism for maltose utilization involving Glk, MalT, Mlc and PtsG has been proposed [Lengsfeld09].
It is possible that high levels of β-D-glucose could accumulate inside the cell under certain conditions. It has been shown that the maltose acetyltransferase product of gene maa efficiently acetylates both maltose and β-D-glucose (not shown). Evidence suggests that acetylation could be a detoxification mechanism in which acetylated β-D-glucose diffuses from the cell [Boos81, Brand91].
There is evidence that β-D-glucose can be oxidized to glucono-δ-lactone (glucono-1,5-lactone) by inner membrane glucose dehydrogenase. However, the fate of the glucono-δ-lactone remains unclear. It has been reported that membrane vesicles from glucose-grown E. coli oxidized glucose to gluconate in the presence of pyrrolo-quinoline quinone, a cofactor for glucose dehydrogenase [vanSchie85]. A gluconolactonase (EC 18.104.22.168) has been partially characterized in E. coli, but its D-gluconate product was not specifically identified [Hucho72] and no gene encoding this enzyme has been identified. D-gluconate can be degraded by a glucose utilization pathway that was described early [Cohen51], as shown in the pathway link. In addition, more recent work suggested possible excretion of D-gluconate although this compound was not specifically identified [Sashidhar10].
α-D-glucose-1-phosphate is reversibly converted by phosphoglucomutase to α-D-glucose-6-phosphate. α-D-glucose-1-phosphate is used in glycogen biosynthesis (see glycogen biosynthesis I (from ADP-D-Glucose)) and is produced during glycogen degradation (see glycogen degradation I (bacterial)). α-D-glucose-6-phosphate may spontaneously convert to β-D-glucose-6-phosphate in the physiological pH range [Salas65]. In addition, a glucose-6-phosphate 1-epimerase had been identified in E. coli ATCC 9637 that could catalyze this production of β-D-glucose 6-phosphate.
Several phosphatases may catalyze the production of D-glucose (anomeric form unspecified) from α-D-glucose-1-phosphate. The product of gene agp is a periplasmic enzyme that scavenges glucose and allows E. coli to grow with glucose-1-phosphate as sole carbon source [Pradel91] and in [Lee03c].
Review: Mayer, C. and W. Boos (2005) "Hexose/Pentose and Hexitol/Pentitol Metabolism." EcoSal module 3.4.1 [ECOSAL]
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Pradel91: Pradel E, Boquet PL (1991). "Utilization of exogenous glucose-1-phosphate as a source of carbon or phosphate by Escherichia coli K12: respective roles of acid glucose-1-phosphatase, hexose-phosphate permease, phosphoglucomutase and alkaline phosphatase." Res Microbiol 1991;142(1);37-45. PMID: 1648777
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vanSchie85: van Schie BJ, Hellingwerf KJ, van Dijken JP, Elferink MG, van Dijl JM, Kuenen JG, Konings WN (1985). "Energy transduction by electron transfer via a pyrrolo-quinoline quinone-dependent glucose dehydrogenase in Escherichia coli, Pseudomonas aeruginosa, and Acinetobacter calcoaceticus (var. lwoffi)." J Bacteriol 163(2);493-9. PMID: 3926746
Brautaset98: Brautaset T, Petersen S, Valla S (1998). "An experimental study on carbon flow in Escherichia coli as a function of kinetic properties and expression levels of the enzyme phosphoglucomutase." Biotechnol Bioeng 58(2-3);299-302. PMID: 10191405
CletonJansen90: Cleton-Jansen AM, Goosen N, Fayet O, van de Putte P (1990). "Cloning, mapping, and sequencing of the gene encoding Escherichia coli quinoprotein glucose dehydrogenase." J Bacteriol 172(11);6308-15. PMID: 2228962
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Cozier95: Cozier GE, Anthony C (1995). "Structure of the quinoprotein glucose dehydrogenase of Escherichia coli modelled on that of methanol dehydrogenase from Methylobacterium extorquens." Biochem J 312 ( Pt 3);679-85. PMID: 8554505
Cozier99: Cozier GE, Salleh RA, Anthony C (1999). "Characterization of the membrane quinoprotein glucose dehydrogenase from Escherichia coli and characterization of a site-directed mutant in which histidine-262 has been changed to tyrosine." Biochem J 1999;340 ( Pt 3);639-47. PMID: 10359647
Curtis75: Curtis SJ, Epstein W (1975). "Phosphorylation of D-glucose in Escherichia coli mutants defective in glucosephosphotransferase, mannosephosphotransferase, and glucokinase." J Bacteriol 122(3);1189-99. PMID: 1097393
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Elias00: Elias MD, Tanaka M, Izu H, Matsushita K, Adachi O, Yamada M (2000). "Functions of amino acid residues in the active site of Escherichia coli pyrroloquinoline quinone-containing quinoprotein glucose dehydrogenase." J Biol Chem 275(10);7321-6. PMID: 10702303
Elias01: Elias M, Tanaka M, Sakai M, Toyama H, Matsushita K, Adachi O, Yamada M (2001). "C-terminal periplasmic domain of Escherichia coli quinoprotein glucose dehydrogenase transfers electrons to ubiquinone." J Biol Chem 276(51);48356-61. PMID: 11604400
Elias04: Elias MD, Nakamura S, Migita CT, Miyoshi H, Toyama H, Matsushita K, Adachi O, Yamada M (2004). "Occurrence of a bound ubiquinone and its function in Escherichia coli membrane-bound quinoprotein glucose dehydrogenase." J Biol Chem 279(4);3078-83. PMID: 14612441
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