arabinose

Arabinose is a naturally occurring aldopentose monosaccharide with the chemical formula C5H10O5. It exists in two enantiomeric forms, D-arabinose and L-arabinose, with D-arabinose being the more common form found in nature.

In nature, arabinose is a component of plant polysaccharides, particularly arabinans and arabinoxylans, which are part of hemicelluloses in plant cell walls. It also occurs in gum arabic and other plant-derived polymers. Free arabinose is less common; most biological relevance arises from its linkages within larger carbohydrate molecules.

Metabolism and genetics: In bacteria such as Escherichia coli, L-arabinose is catabolized via the arabinose operon, consisting of the enzymes AraA (L-arabinose isomerase), AraB (L-ribulokinase), and AraD (ribulose-5-phosphate epimerase). L-arabinose is converted to xylulose-5-phosphate, which enters the pentose phosphate pathway. Expression of the arabinose operon is regulated by the AraC protein. The pBAD promoter, derived from this system, is widely used in molecular biology to achieve arabinose-inducible gene expression in E. coli.

Applications and notes: Arabinose is used in biotechnology as part of inducible expression systems (notably the pBAD system) to control gene expression in bacterial hosts. In nutrition and pharmacology, L-arabinose has been studied as an inhibitor of intestinal sucrase, with potential to reduce postprandial glucose absorption, though it is not a standard medical treatment. Beyond biology and health, arabinose derivatives and its enantiomers serve as building blocks in chemical synthesis and research.