Detoxification of methylglyoxal by the mouse aldo-keto reductase

Abstract

Methylglyoxal is a toxic metabolite known to accumulate in various cell type. We detected in vivo conversion of methylglyoxal (MG) to acetol by $^1H-NMR$ when extract of mouse tissue crude extract was incubated with 3 mM MG and 1 mM NADPH as a cofactor. For purification of the mouse enzyme associated with MG reduction, we applied mouse kidney extract to two different ionic exchange chromatography. The MG reduction activities were detected by an assay with NADPH oxidation. Furthermore, we selected three genes, AKR1A4, AKR1B8, and AKR1C20, to test whether they show MG reductase activity. We purified these AKRs and determined their $K_m$, $K_{cat}$, and $K_{cat}/K_m$ values, with optimum pH for methylglyoxal. The $K_m$ values of AKR1A4 and AKR1B8 for MG are 1.1 - 1.3 mM. However, The $K_{cat}/K_m$ value of AKR1A4 is higher than that of AKR1B8 by about 20 folds. The specific activity of 26 fold purified AKR1A4 for MG is 16801μmole/min/mg, generating acetol as detected by $^1H-NMR$. The results imply that the glutathione-independent detoxification of MG to acetol can occur by the aldo-keto reductase AKR1A4.