IDENTITY OF A MAJOR 3-DEOXYGLUCOSONE-REDUCING ENZYME WITH ALDEHYDE REDUCTASE IN RAT-LIVER ESTABLISHED BY AMINO-ACID SEQUENCING AND CDNA EXPRESSION

We have purified a rat liver enzyme that catalyzes the NADPH-dependent reduction of 3-deoxyglucosone (3-DG), a major intermediate in the Mai llard reaction and a potent cross-linker responsible for the polymeriz ation of proteins. Comparison of the amino acid (aa) sequences of nine peptides obtained from the rat 3-DG-reducing enzyme by lysyl-endopept idase digestion with the aa sequence of human aldehyde reductase (ALR) [Bohren et al., J. Biol. Chem. 266 (1991) 24031-24037] strongly sugge sted that the purified enzyme was rat ALR. We cloned the cDNA encoding ALR from a rat kidney cDNA library using a human ALR cDNA fragment, a mplified by polymerase chain reaction, as a probe. All nine peptides i dentified in the purified rat 3-DG-reducing enzyme were found in the a a sequence deduced from the rat ALR cDNA. Moreover, cell extract from COS-1 cells transfected with the rat ALR cDNA exhibited NADPH-dependen t 3-DG-reducing activity and cross-reacted with antiserum raised again st the purified rat 3-DG-reducing enzyme. All the above data indicate clearly that the 3-DG-reducing enzyme is identical with ALR. Northern blot analysis of total mRNA from a variety of rat tissues showed fairl y high levels of expression of ALR mRNA. This suggests that sufficient ALR is present to detoxify 3-DG when it is formed through the Maillar d reaction in vivo.