The Glyoxalase System

The glyoxalase system is believed to have evolved to detoxify reactive 2-oxoaldehydes, mainly methylglyoxal, that is formed endogenously as a by-product of the triosephosphate isomerase reaction in glycolysis.

The 2-oxoaldehydes are converted into their corresponding 2-hydroxy acids in two consecutive steps, the first catalyzed by glyoxalase I, and the second by glyoxalase II. Glyoxalase I and glyoxalase II are not homologous.

For example, methylglyoxal reacts non-enzymatically with glutathione. The resulting hemithioacetal is a substrate for glyoxalase I which catalyze the formation of S-D-lactoylglutathione. The S-D-lactoylglutathione is then hydrolyzed to D-lactate and glutathione by glyoxalase II. Glutathione functions as an anchor of the substrates in the active sites of the two enzymes.

Glyoxalase II

Glyoxalase II catalyzes the hydrolysis of S-D -lactoylglutathione to form D-lactate and glutathione. Glyoxalase II is a metalloenzyme that is structurally related to other metallohydrolases such as metallo-β-lactamases and aryl sulfatase.

The crystal structure suggested that tyrosine-175 may play a role in the catalysis, acting, for example, as acid/base catalyst. The hydroxyl oxygen of Tyr175 was found to be situated close to both the nitrogen in the peptide bond between glycine and cystein (2.9 ‰), and the sulfur (3.6 ‰), of the substrate analog S-(N-hydroxy-N-bromophenylcarbamoyl)glutathione in the crystal structure of glyoxalase II.

To identify the role of Tyr175, wild-type glyoxalase II and the Tyr175Phe mutant were subjected to steady-state kinetics and pre-equilibrium binding analyses. It was shown that Tyr175 contributes to the binding of the substrate but that the residue does not participate in the hydrolytic cleavage of the thiolester bond:

Ridderström, M., Jemth, P., Cameron, A. D., Jones, T. A., and Mannervik, B. (2000) The active-site residue Tyr-175 in human glyoxalase II contributes to binding of glutathione derivatives. Biochim. Biophys. Acta 1481, 344-348 [abstract]



The crystal structure of human glyoxalase II:
Cameron, A. D., Ridderström, M., Olin, B., Mannervik, B. (1999) Crystal structure of human glyoxalase II and its complex with a glutathione thiolester substrate analogue. Structure 7, 1067-1078 [abstract]