Glucuronic acid

Glucuronic acid (from Ancient Greek γλυκύς "sweet" + οὖρον "urine") is an uronic acid that was first isolated from urine (hence the name). It is found in many gums such as Gum arabic (ca. 18 %) and Xanthan, and is important for the metabolism of microorganisms, plants and animals.

Properties

Glucuronic acid is a sugar acid derived from glucose, with its sixth carbon atom oxidized to a carboxylic acid. In living beings, this primary oxidation occurs with UDP-α-D-glucose (UDPG), not with the free sugar.

Glucuronic acid, like its precursor glucose, can exist as a linear (carboxo-)aldohexose (< 1 %), or as a cyclic hemiacetal (furanose or pyranose). Aldohexoses such as D-glucose are capable of forming two furanose forms (α and β) and two pyranose forms (α and β). By the Fischer convention, glucuronic acid has two stereoisomers (enantiomers), D- and L-glucuronic acid, depending on its configuration at C-5. Most physiological sugars are of the D-configuration. Due to ring closure, cyclic sugars have another asymmetric carbon atom (C-1), resulting in two more stereoisomers, named anomers. Depending on the configuration at C-1, there are two anomers of glucuronic acid, α- and β-form. In β-D-glucuronic acid the C-1 hydroxy group is on the same side of the pyranose ring as the carboxyl group. In the free sugar acid, the β-form is prevalent (~ 64 %), whereas in the organism, the α-form UDP-α-D-glucuronic acid (UDPGA) predominates.