This view shows enzymes only for those organisms listed below, in the list of taxa known to possess the pathway. If an enzyme name is shown in bold, there is experimental evidence for this enzymatic activity.
|Superclasses:||Degradation/Utilization/Assimilation → Aldehyde Degradation|
|Detoxification → Methylglyoxal Detoxification|
Methylglyoxal is produced in small amounts during glycolysis (via glycerone phosphate), fatty acid metabolism (via acetone), and protein metabolism (via aminoacetone). Methylglyoxal is highly toxic, most likely as a result of its interaction with protein side chains (see [Kalapos99] for a review). There are several pathways for the detoxification of methylglyoxal, based on different enzymes that are able to convert methylglyoxal to less toxic compounds. These enzymes include glyoxalase enzymes, methylglyoxal reductases, aldose reductases, aldehyde reductases and methylglyoxal dehydrogenases.
About This Pathway
Methylglyoxal dehydrogenases catalyze the direct oxidation of methylglyoxal to pyruvate. The first enzyme that was shown to catalyze this reaction was partially purified from sheep liver [Monder67]. That enzyme was able to utilize both NAD and NADP, and was not specific for methylglyoxal. However, later work suggested that this enzyme might have been a mixture of two different enzymes - one specific for NAD and the other for NADP. Such two enzymes were purified from goat liver, and were shown to be of exactly the same size - 42 kDa [Ray82].
NAD-specific enzymes have also been detected in microorganisms. Higgins and Turner reported that cell extracts of Pseudomonas sp. NCIB 8858 catalyzed the direct oxidation of methylglyoxal to pyruvate by an enzyme which they named methylglyoxal oxidase. The specific activity of the extracts was 35 nmoles/mg protein per min, and was maximal at pH 7.9. The enzyme was inducible by growth on (R)-1-aminopropan-2-ol, and the Km of the enzyme was 30 μM [Higgins69]. Another such enzyme has been purified from Pseudomonas putida [Rhee87].
This pathway is probably not present in yeast or higher plants [Murata89].
Variants: methylglyoxal degradation I, methylglyoxal degradation II, methylglyoxal degradation III, methylglyoxal degradation IV, methylglyoxal degradation V, methylglyoxal degradation VI, methylglyoxal degradation VIII
Ray82: Ray S, Ray M (1982). "Purification and characterization of NAD and NADP-linked alpha-ketoaldehyde dehydrogenases involved in catalyzing the oxidation of methylglyoxal to pyruvate." J Biol Chem 257(18);10566-70. PMID: 7107625
Rhee87: Rhee, H.I., Watanabe, K., Murata, K., Kimura, A. (1987). "Metabolism of 2-oxoaldehyde in bacteria: oxidative conversion of methylglyoxal to pyruvate by an enzyme from Pseudomonas putida." Agric. Biol. Chem. 51: 1059-1066.
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