hydroxypyruvate

Hydroxypyruvate, also known as 3-hydroxy-2-oxopropanoate, is a small organic molecule classified as a beta-hydroxy alpha-keto acid. It exists in enantiomeric forms (L- and D-), and in solution is typically present as its conjugate base, hydroxypyruvate. It is a metabolic intermediate rather than a primary metabolite in most organisms.

In plants and some microorganisms, hydroxypyruvate is a key intermediate in the photorespiratory pathway. It is formed through the transamination of glyoxylate with L-alanine, a reaction catalyzed by alanine:glyoxylate aminotransferase, yielding hydroxypyruvate and glycine. This step links glycolate/glyoxylate metabolism to downstream pathways that recover carbon for photosynthesis.

The next step in photorespiration is the reduction of hydroxypyruvate to glycerate by hydroxypyruvate reductase. Glycerate is then phosphorylated to 3-phosphoglycerate, which re-enters the Calvin cycle or associated carbon fixation processes. Thus, hydroxypyruvate serves as a branching point between glyoxylate metabolism and the central carbon metabolism of photosynthetic organisms.

Beyond plant biology, hydroxypyruvate can arise in other metabolic contexts concerning serine and glyoxylate interconversions and is studied as a substrate for various aminotransferases in enzymology. Its chemistry as a beta-hydroxy alpha-keto acid makes it a useful model compound for investigations into carbon metabolism and enzyme mechanisms.

See also: glyoxylate, glycerate, photorespiration, alanine:glyoxylate aminotransferase.