alpha14Dgalacturonic

Alpha-1,4-D-galacturonic acid, sometimes represented as alpha14Dgalacturonic, denotes the D-galacturonic acid residue linked by an alpha-1,4 glycosidic bond in polysaccharides. It is the repeating monomer unit of homogalacturonan, a linear pectic polymer that constitutes a major portion of plant primary cell walls. In this context, each residue is the uronic acid form of galactose, bearing a carboxyl group at C-6, which confers acidity to the molecule.

In homogalacturonan, the residues are connected by alpha-1,4 linkages, creating a long, unbranched chain. The carboxyl groups can exist as free acids or, more commonly in plant tissues, as methyl esters (methyl galacturonate) within the pectin matrix. De-esterification by pectin methylesterase increases negative charge density and enables calcium-mediated cross-linking between chains, forming gel networks known as the egg-box model.

Natural occurrence and function: alpha-14-D-galacturonic units are abundant in plant cell walls and are central to pectin structure and function. The polymer contributes to cell wall porosity, rigidity, and adhesion between cells, and it plays a key role in plant growth and defense responses. In addition, pectins rich in galacturonic acid are widely used industrially as gelling, thickening, and stabilizing agents in food, pharmaceutical, and cosmetic products.

Biosynthesis and metabolism: Activated sugar donors, such as UDP-D-galacturonate, are used by plant glycosyltransferases to assemble homogalacturonan in the Golgi, after which the polymer is secreted to the cell wall. In humans, galacturonic acid is not a dietary essential, but pectin-derived fragments can be fermented by gut microbiota.

See also: pectin, homogalacturonan, galacturonic acid, plant cell wall, calcium pectate.