The aldo-keto reductase family includes a number of related monomeric NADPH-dependent oxidoreductases, such as aldehyde reductase, aldose reductase, prostaglandin F synthase, xylose reductase, rho crystallin, and many others [PMID:2498333]. All possess a similar structure, with a beta-alpha-beta fold characteristic of nucleotide binding proteins [PMID:2105951]. The fold comprises a parallel beta-8/alpha-8-barrel, which contains a novel NADP-binding motif. The binding site is located in a large, deep, elliptical pocket in the C-terminal end of the beta sheet, the substrate being bound in an extended conformation. The hydrophobic nature of the pocket favours aromatic and apolar substrates over highly polar ones [PMID:1621098].

Binding of the NADPH coenzyme causes a massive conformational change, reorienting a loop, effectively locking the coenzyme in place. This binding is more similar to FAD- than to NAD(P)-binding oxidoreductases [PMID:1447221].

Some proteins of this entry contain a K+ ion channel beta chain regulatory domain; these are reported to have oxidoreductase activity [PMID:10884227].