Cloning and expression of carbonyl reductase from rat testis

Carbonyl reductase is a cytosolic, monomeric, NADPH-dependent oxidoreductase with broad specificity for carbonyl compounds and a general distribution in human and many animal tissues. A carbonyl-reductase-like enzyme is exclusively expressed in rat reproductive tissues and adrenal glands. To understand the structural and functional relationships between the two enzymes, we cloned and sequenced the cDNA for the enzyme from rat testis and overexpressed the encoded protein in Escherichia coli. Three types of cDNA coding for the same protein but differing in their 5'-untranslated regions were isolated. The encoded protein had the same length as, and showed 86% positional identity with, carbonyl reductase from human placenta and liver. The recombinant enzyme exhibited the same substrate specificity and susceptibility to inhibitors as the enzyme isolated from rat testis, and also closely resembled human carbonyl reductase. Similar to the human enzyme, the recombinant rat enzyme catalyzed its own modification by pyruvate and 2-oxoglutarate, respectively. We conclude that carbonyl reductase from rat testis and human tissues represent species-specific forms of the same enzyme.