Glyoxalases

Glyoxalases are enzymes that detoxify reactive aldehydes, particularly methylglyoxal, a byproduct of glycolysis and metabolism. The classical glyoxalase system consists of two enzymes, glyoxalase I (GLO1) and glyoxalase II (GLO2), which use the tripeptide glutathione (GSH) to convert methylglyoxal to D-lactate via the intermediate S-D-lactoylglutathione. A separate activity known as glyoxalase III (GLO3) has been described in some organisms as a single-step, GSH-independent route to D-lactate.

Mechanism: The canonical cycle begins when methylglyoxal reacts non-enzymatically with GSH to form a hemithioacetal. GLO1 catalyzes isomerization to S-D-lactoylglutathione, which GLO2 hydrolyzes to D-lactate, regenerating GSH. The overall reaction detoxifies reactive methylglyoxal and preserves cellular GSH.

Distribution and function: Glyoxalases are widespread in bacteria, plants, and animals. In most eukaryotes, GLO1 and GLO2 are cytosolic enzymes, with plant species sometimes bearing additional isoforms targeting organelles. The system protects proteins, nucleic acids, and lipids from glycation and oxidative stress by removing methylglyoxal and related reactive carbonyl species.

Clinical and research relevance: Increased methylglyoxal can contribute to advanced glycation end products and cellular dysfunction; dysregulation of glyoxalases has been studied in aging, diabetes complications, neurodegeneration, and cancer. As such, glyoxalases, particularly GLO1, are explored as potential therapeutic targets or biomarkers, though findings are context-dependent.