CLONING OF A RAT CDNA-ENCODING RETINOL DEHYDROGENASE ISOZYME TYPE-III

The primary and rate-limiting step in retinoic acid (RA) biosynthesis requires the conversion of retinol into retinal. Previously, two genes encoding retinol dehydrogenases (RoDH), which recognize hole-cellular retinol-binding protein as substrate, had been cloned, expressed and identified as members of the short-chain dehydrogenase/reductase (SDR) gene family. This work reports the cloning of a cDNA encoding a third RoDH isozyme, RoDH(III). The deduced amino-acid sequence of RoDH(III) indicates 97.8% identity with RoDH(I) and 82.3% identity with RoDH(II ). RNase protection assays revealed RoDH(III) mRNA expression only in rat liver, in contrast to RoDH(I) and RoDH(II), which had their mRNA e xpressed in rat liver, kidney, lung, testis and brain. These data exte nd the insight that a subfamily of SDR isozymes, tissue-distinctively expressed, catalyzes the first step in RA biogenesis.