IN-VIVO GLYCATION OF ALDEHYDE REDUCTASE, A MAJOR 3-DEOXYGLUCOSONE REDUCING ENZYME - IDENTIFICATION OF GLYCATION SITES

We have reported that the enzyme which reduces 3-deoxyglucosone (3-DG), a major intermediate and a potent cross-linker in the Maillard reaction, is identical with aldehyde reductase [Takahashi, M., Fujii, J., Teshima, T., Suzuki, K., Shiba, T., and Taniguchi, N. (1993) Gene 127, 249-253]. The enzyme purified from normal rat liver was found to be partially glycated as judged by binding to a boronate column and reactivity to anti-epsilon-hexitol lysine Igc. Sites of in vivo glycation of rat Liver aldehyde reductase were identified by sequencing of digested peptides labeled with NaB[H-3](4) and by mass spectrometry. The major glycated sites were lysines 67, 84, and 140. The glycated enzyme had low catalytic efficiency (k(cat)/K-m) as compared to the nonglycated form. In streptozotocin-induced diabetic rats, the glycated form was significantly increased in kidneys. Because the enzyme plays a role in detoxifying 3-DG formed through the Maillard reaction in vivo, glycation of aldehyde reductase and reduction of its activity may result in the metabolic imbalance under diabetic conditions.