Identification of 3-deoxyglucosone dehydrogenase as aldehyde dehydrogenase 1A1 (retinaldehyde dehydrogenase 1)

Abstract

One of the metabolic fates of 3-deoxyglucosone, a product of protein deglycation and a potent glycating agent, is to be oxidized to 2-keto-3-deoxygluconate, but the enzyme that catalyzes this reaction is presently unknown. Starting from human erythrocytes, which are known to convert 3-deoxyglucosone to 2-keto-3-deoxygluconate, we have purified to near homogeneity a NAD-dependent dehydrogenase that catalyzes this last reaction at neutral pH. Sequencing of a 55 kDa band co-eluting with the enzymatic activity in the last step indicated that it corresponded to aldehyde dehydrogenase 1A1 (ALDH1A1), an enzyme known to catalyze the oxidation of retinaldehyde to retinoic acid. Overexpression of human ALDH1A1 in HEK cells led to a more than 20-fold increase in 3-deoxyglucosone dehydrogenase activity. In mouse tissues 3-deoxyglucosone dehydrogenase activity was highest in liver, intermediate in lung and testis, and negligible or undetectable in other tissues, in agreement with the tissue distribution of ALDH1A1 mRNA. 3-deoxyglucosone dehydrogenase activity was undetectable in tissues from ALDH1A1(-/-) mice. ALDH1A1 appears therefore to be the major if not the only enzyme responsible for the oxidation of 3-deoxyglucosone to 2-keto-3-deoxygluconate. The urinary excretion of 2-keto-3-deoxygluconate amounted to 16.7 micromol/g creatinine in humans, indicating that 3-deoxyglucosone may be quantitatively a more important substrate than retinaldehyde for ALDH1A1.

Figure 1. Identification of 3-deoxyglucosone dehydrogenase as aldehyde dehydrogenase 1A1 (ALDH1A1)

Panel A shows the elution profile of 3-DGDH from the UnoQ column, the last purification step. Twenty μl of the indicated fractions were loaded on a SDS-PAGE gel, which was stained with Coomassie blue (panel B). The indicated band was cut from the gel, submitted to trypsin digestion and analyzed by mass spectrometry. Panel C shows the identified peptides (underlined) in the sequence of ALDH1A1 (gi-21361176).

Figure 2. Distribution of 3-deoxyglucosone dehydrogenase in mouse tissues

Results shown are the means of three experiments ± SEM.