galacturonic

Galacturonic is an adjective relating to galacturonic acid, a uronic acid derived from galactose by oxidation of the terminal primary alcohol to a carboxyl group. The most common form in biology is D-galacturonic acid, which exists as the galacturonate anion at neutral pH. It is a key building block in various plant polysaccharides.

In plants, galacturonic acid residues are a major component of pectin, particularly in homogalacturonan, a linear polymer of alpha-D-galacturonic acid units linked by 1→4 glycosidic bonds. Many galacturonic acid units in pectin are esterified with methanol at the carboxyl group, producing methyl esters that influence the polymer’s properties. The degree of esterification affects gelling behavior and interactions with divalent cations such as calcium.

Biosynthesis and incorporation into polysaccharides involve activation as UDP-galacturonate, formed from UDP-glucose through a UDP-glucose dehydrogenase–mediated pathway. Galacturonosyltransferases then incorporate the activated residues into growing pectin chains within the plant cell wall. This process is part of the broader cell-wall biosynthetic machinery that shapes plant structure and integrity.

Biological and industrial relevance: pectin, a heterogeneous polymer rich in galacturonic acid, serves as a gelling and thickening agent in foods and as a component affecting plant physiology. Enzymes called polygalacturonases and other pectinases release galacturonic acid and oligogalacturonides during fruit ripening and digestion.