The Aldo-Keto Reductase Superfamily

Aldehyde reductase [EC 1.1.1.2] and aldose reductase [EC 1.1.1.21] are monomeric NADPH-dependent oxidoreductases having wide substrate specificities for carbonyl compounds. These enzymes are implicated in the development of diabetic complications by catalyzing the reduction of glucose to sorbitol. Enzyme inhibition as a direct pharmacokinetic approach to the prevention of diabetic complications resulting from the hyperglycemia of diabetes has not been effective because of nonspecificity of the inhibitors and some appreciable side effects. To understand the structural and evolutionary relationship of these enzymes, we cloned and sequenced cDNAs coding for aldose and aldehyde reductases from human liver and placental cDNA libraries. Human placental aldose reductase (open reading frame of 316 amino acids) has a 65% identity (identical plus conservative substitutions) to human liver and placental aldehyde reductase (open reading frame of 325 amino acids). The two sequences have significant identity to 2,5-diketogluconic acid reductase from corynebacterium, frog rho-crystallin, and bovine lung prostaglandin F synthase (reductase). Southern hybridization analysis of human genomic DNA indicates a multigene system for aldose reductase, suggesting the existence of additional proteins. Thus, the aldo-keto reductase superfamily of proteins may have a more significant and hitherto not fully appreciated role in general cellular metabolism.