Glucuronic acid

Glucuronic acid
Names
IUPAC name
(2S,3S,4S,5R,6R)-3,4,5,6-​Tetrahydroxyoxane-2-carboxylic acid
Other names
β-D-glucopyranuronic acid
Identifiers
6556-12-3 Yes
ChEBI CHEBI:28860 
ChemSpider 392615 Yes
DrugBank DB03156 Yes
Jmol-3D images Image
KEGG C00191 Yes
MeSH Glucuronic+acid
PubChem 441478
UNII 8A5D83Q4RW Yes
Properties
Molecular formula
 C6H10O7
Molar mass 194.14 g·mol−1
Melting point 159 to 161 °C (318 to 322 °F; 432 to 434 K)[1]
Except where noted otherwise, data is given for materials in their standard state (at 25 °C (77 °F), 100 kPa)
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Infobox references
Not to be confused with Gluconic acid.

Glucuronic acid (from Ancient Greek γλυκύς "sweet" + οὖρον "urine") is a carboxylic acid. Its structure is similar to that of glucose. However, glucuronic acid's sixth carbon is oxidized to a carboxylic acid. Its formula is C6H10O7.

The salts and esters of glucuronic acid are known as glucuronates; the anion C6H9O7− is the glucuronate ion.

Glucuronic acid should not be confused with gluconic acid, a linear carboxylic acid resulting from the oxidation of a different carbon of glucose.

Functions

Proteoglycans

Glucuronic acid is common in carbohydrate chains of proteoglycans. It is part of mucous animal secretions (such as saliva), cell glycocalyx, and intercellular matrix (for instance hyaluronan).

Glucuronidation of toxic substances

Main article: Glucuronidation

In the animal body, glucuronic acid is often linked to the xenobiotic metabolism of substances such as drugs, pollutants, bilirubin, androgens, estrogens, mineralocorticoids, glucocorticoids, fatty acid derivatives, retinoids, and bile acids. These linkages involve glycosidic bonds, and this linkage process is known as glucuronidation.[2] Glucuronidation occurs mainly in the liver, although the enzyme responsible for its catalysis, UDP-glucuronyltransferase, has been found in all major body organs, e.g., intestine, kidneys, brain, adrenal gland, spleen, and thymus.[3][4]

The substances resulting from glucuronidation are known as glucuronides (or glucuronosides) and are typically much more water-soluble than the non-glucuronic acid-containing substance from which they were originally synthesised. The human body uses glucuronidation to make a large variety of substances more water-soluble, and, in this way, allow for their subsequent elimination from the body through urine or faeces (via bile from the liver). Hormones may also be glucuronidated to allow for easier transport around the body. Pharmacologists have linked drugs to glucuronic acid to allow for more effective delivery of a broad range of substances. Sometimes toxic substances are also less toxic after glucuronidation.

The conjugation of xenobiotic molecules with hydrophilic molecular species such as glucuronic acid is known as phase II metabolism.

The β-D methyl glycoside of glucuronic acid in the low energy 4C1 conformation

Use

Determination of urinary steroids and of steroid conjugates in blood.

Both glucuronic acid and gluconic acid are reported to be contained in some commercially available brands of Kombucha.[5]

In all plants and mammals-other than guinea pigs and primates-glucuronic acid is a precursor of ascorbic acid, also known as vitamin C.[6]

Conformation

Unlike its C5 epimer iduronic acid, which may occur in a number of conformations, glucuronic acid occurs in predominantly the 4C1 conformation.[7]

Glucuronidases

Glucuronidases are those enzymes that hydrolyze the glycosidic bond between glucuronic acid and some other compound.

Notes

  1. ↑ D-Glucuronic acid at Sigma-Aldrich
  2. ↑ King C, Rios G, Green M, Tephly T (2000). "UDP-glucuronosyltransferases". Curr. Drug Metab. 1 (2): 143–61. doi:10.2174/1389200003339171. PMID 11465080.
  3. ↑ Ohno, Shuji; Nakajin, Shizuo (2008-10-06). "Determination of mRNA Expression of Human UDP-Glucuronosyltransferases and Application for Localization in Various Human Tissues by Real-Time Reverse Transcriptase-Polymerase Chain Reaction". Drug Metabolism and Disposition (American Society for Pharmacology and Experimental Therapeutics) 37 (1): 32–40. doi:10.1124/dmd.108.023598. Retrieved 2010-11-07.
  4. ↑ Bock K, Köhle C (2005). "UDP-glucuronosyltransferase 1A6: structural, functional, and regulatory aspects". Methods enzymol. 400: 57–75. doi:10.1016/S0076-6879(05)00004-2. PMID 16399343.
  5. ↑ Blanc, P.J. (February 1996). "Characterization of the tea fungus metabolites". Biotechnology Letters 18 (2): 139. doi:10.1007/BF00128667.
  6. ↑ Harvey, Richard (2011). Biochemistry (5th Edition). Philadelphia: Wolters Kluwer: Lippincott Williams and Wilkins. p. 161. ISBN 978-1-60831-412-6.
  7. ↑ Ferro, D. R. Provasoli, A. (1990). "Conformer populations of L-iduronic acid residues in glycosaminoglycan sequences". Carbohydr. Res. 195 (2): 157–167. doi:10.1016/0008-6215(90)84164-P. PMID 2331699.

References