Dkynurenine

D-kynurenine, or D-kynurenine, is the D-enantiomer of kynurenine, a metabolite in the tryptophan degradation pathway. In mammals, kynurenine is produced from tryptophan via indoleamine 2,3-dioxygenase or tryptophan 2,3-dioxygenase and then proceeds to form several downstream metabolites, such as kynurenic acid and quinolinic acid. D-kynurenine is the less common enantiomer and is not a major component of typical human kynurenine metabolism.

Occurrence and biosynthesis: D-kynurenine can be formed in trace amounts by non-enzymatic racemization or is produced by certain microorganisms. When used in research, it is typically administered exogenously to study stereospecificity in enzymes of the kynurenine pathway or to probe biological responses to the D-enantiomer.

Enzymology and metabolism: Many human kynurenine pathway enzymes show strict preference for L-kynurenine, making D-kynurenine a poor substrate or potential inhibitor in several reactions. Some microbial or non-human enzymes can metabolize D-kynurenine, but the precise metabolic fate and physiological consequences of D-kynurenine in humans remain incompletely understood.

Biological relevance: The physiological role of D-kynurenine in humans is not well defined. It is mainly of interest as a research tool to investigate enzyme specificity, transporter interactions, and potential neuroactive effects associated with kynurenine enantiomers. There is limited evidence for a routine endogenous function for D-kynurenine.

See also: Kynurenine pathway; L-kynurenine; kynurenic acid; tryptophan metabolism.