alphaDgalacturonic

Alpha-D-galacturonic acid, often referred to as α-D-galacturonate, is the α anomer of D-galacturonic acid, a hexuronic acid formed by oxidation of the sixth carbon of galactose to a carboxyl group. In solution, it exists in mutarotation with its β anomer. This sugar acid is a key component of plant polysaccharides, most notably pectin, where it contributes to the acidic character and structural properties of the polymer.

In pectin, the repeating units are typically linked α(1→4) to form polygalacturonic acid chains. Many galacturonic acid residues can be methyl-esterified at the carboxyl group, producing methyl galacturonate derivatives that alter solubility and gelling behavior. The carboxylate groups render pectin negatively charged at neutral pH, influencing interactions with water and with divalent cations.

Biosynthesis and metabolism involve the donor UDP-galacturonic acid, incorporated into growing pectin chains by galacturonosyltransferases during cell wall formation. Pectin methylesterases can remove methyl groups, increasing the density of free carboxylates and enabling calcium-mediated cross-linking. This cross-linking, described by the egg-box model, underpins gel formation and wall rigidity in plant tissues.

Applications and significance include the use of pectin, rich in α-D-galacturonic acid, as a gelling agent and thickener in food products. Its properties depend on the degree of esterification, calcium availability, and enzymatic modification, making α-D-galacturonic acid a central feature of pectin chemistry and plant cell wall biology.