Aldose and aldehyde reductase in animal tissues.

The aldehyde reductases comprise a group of monomeric NADPH-dependent oxidoreductases with a broad and similar substrate specificity. Three major reductases, ALR1, ALR2, and ALR3, occur in tissues. The predominant one, ALR1, is aldehyde reductase; ALR2 is aldose reductase, an enzyme implicated in the etiology of diabetic complications; and ALR3 is carbonyl reductase, the only reductase with any affinity for ketones. ALR1 and ALR2 are immunologically nonrelated, and little immunologic relatedness exists between aldehyde reductases, particularly ALR1, from different species. The evolutionary relatedness of ALR2, however, may be closer, particularly among the primates. ALR2 from human and monkey tissues are immunologically identical.