Dmalate

D-malate, or D-malic acid, is the dextrorotatory enantiomer of malic acid, a four-carbon dicarboxylic acid with a hydroxyl group at the 2-position. The two enantiomers, D-malate and L-malate, share identical chemical formulas and most physical properties, but rotate plane-polarized light in opposite directions. In solution they are stereoisomers and interconversion occurs only by racemization.

In biology, L-malate is the more common form and serves as an intermediate in the citric acid cycle and in gluconeogenesis. D-malate occurs only in small amounts in some organisms or under certain conditions. It can arise from racemization of L-malate or be produced by specific enzymes in microbes that metabolize the D-enantiomer.

Enzymatically, D-malate can be oxidized to oxaloacetate by D-malate dehydrogenase, using NAD+ as cofactor, similar to the reaction catalyzed by the more widespread L-malate dehydrogenase. Some microbes also possess enzymes that interconvert malate enantiomers, enabling D-malate to feed into central metabolism via oxaloacetate.

Applications and occurrence: D-malate is less common in industry than L-malate. It can be prepared synthetically or obtained via resolution of racemic malic acid, and may be used as a chiral building block in organic synthesis in cases where the D-enantiomer is required.

Safety and regulation: Malic acid and its enantiomers are generally recognized as safe for use as food additives; regulatory distinctions for D-malate specifically are not widely emphasized beyond those for malic acid.

See also: L-malate, malic acid, citric acid cycle, malate dehydrogenase, D-malate dehydrogenase.