Subsystem: D-Galacturonate and D-Glucuronate Utilization

This subsystem's description is:

The glucuronides are then mostly excreted out of the body via the bile ducts into the intestine, through apocrine secretions, and through the bladder into the urinary tract. The conjugated compounds are typically much more water soluble than the respective aglycones and are often biochemically and biologically inactive. The glucuronidation and excretion of such compounds have thus often been described as detoxification.
In the intestine and on the skin, large populations of commensal and symbiotic microorganisms have access to the diverse glucuronides, and some have evolved the ability to metabolize these compounds. The enterobacterium Escherichia coli colonizes all known vertebrates. Most E. coli strains living in natural environments possess β-d-glucuronidase (EC 3.2.1.31) and are able to acquire glucuronides as nutrients. β-d-Glucuronidase is an intracellular hydrolase that catalyzes the hydrolysis of β-d-glucuronides within the cytoplasm of E. coli. The glycone released can then be used as a carbon source. Almost any aglycone conjugated in a hemiacetal linkage to the C-1 hydroxyl of glucuronate in the β-configuration can be cleaved by β-d-glucuronidase, except for some thio-β-d-glucuronides.
Some strains of B. subtilis can use glucuronate and galacturonate as primary carbon sources. Polymethylgalacturonate, or pectin, is a constituent of plant cell walls and thus is found in the soil. Extracellular pectate lyases, produced by Erwinia chrysanthemi and many other bacteria, including B. subtilis, convert pectin into oligogalacturonate. Oligogalacturonate can be metabolized into D-galacturonate by enzymes produced by Erwinia sp. In addition, free galacturonate and glucuronate enter Escherichia coli and Erwinia sp. via the exuT transport system.
The uxuA, uxuB, uxaA, uxaB, and uxaC genes of E. coli and E. chrysanthemi encode enzymes that degrade intracellular galacturonate and glucuronate into 2-keto 3-deoxygluconate (KDG), which is further metabolized to pyruvate and 3-phosphoglyceraldehyde. The expression of these genes, including exuT, is negatively regulated by the exuR gene product in these organisms.

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Literature ReferencesD-galacturonic acid catabolism in microorganisms and its biotechnological relevance. Richard P Applied microbiology and biotechnology 2009 Mar19159926
A 35.7 kb DNA fragment from the Bacillus subtilis chromosome containing a putative 12.3 kb operon involved in hexuronate catabolism and a perfectly symmetrical hypothetical catabolite-responsive element. Rivolta C Microbiology (Reading, England) 1998 Apr9579062
The regulatory region of the uxuAB operon in Escherichia coli K12. Blanco C Molecular & general genetics : MGG 1986 Jan3083215
At the periphery of the amidohydrolase superfamily: Bh0493 from Bacillus halodurans catalyzes the isomerization of D-galacturonate to D-tagaturonate. Nguyen TT Biochemistry 2008 Jan 2918171028
Regulation of hexuronate system genes in Escherichia coli K-12: multiple regulation of the uxu operon by exuR and uxuR gene products. Robert-Baudouy J Journal of bacteriology 1981 Jan7007313
The glucuronic acid utilization gene cluster from Bacillus stearothermophilus T-6. Shulami S Journal of bacteriology 1999 Jun10368143
Regulation of Escherichia coli K-12 hexuronate system genes: exu regulon. Portalier R Journal of bacteriology 1980 Sep6997263
Regulation of hexuronate utilization in Bacillus subtilis. Mekjian KR Journal of bacteriology 1999 Jan9882655
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