mannuronic

Mannauronic is commonly used to refer to the properties and residues of mannuronic acid, a uronic sugar derived from mannose. In the polysaccharide alginate, mannuronic acid is one of the two main monomeric units, the other being guluronic acid. The residues are designated as M units in alginate.

Chemical nature and structure: Mannuronic acid is a hexuronic acid that, in alginate, forms β-D-mannuronic acid residues linked by β-1,4 glycosidic bonds. The carboxylate group imparts negative charge to the polymer, enabling interaction with divalent cations and participation in gel formation.

Occurrence and sources: Mannuronic acid is found in alginates produced by brown algae (Phaeophyceae) and by certain bacteria. The M to G ratio varies by source, influencing the physical properties of the resulting polymer, including viscosity and gel strength.

Biological and industrial relevance: Enzymes such as mannuronan C-5-epimerase (AlgG) can convert M residues to G within alginate, altering block structure from M-rich to G-rich sequences and thereby tuning gel characteristics.

Applications and properties: Alginate containing mannuronan units is used as a thickener, stabilizer, and gelling agent in food, pharmaceuticals, wound care, and dental materials. The proportion of M content affects gel flexibility, pore size, and calcium-mediated gel rigidity.

Nomenclature and forms: The term mannuronic commonly refers to residues of D-mannuronic acid; the ionized form is called mannuronate. Polymers rich in M units are sometimes described as mannuronan or M-rich alginates, distinguishing them from G-rich variants.