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 holo-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 expressed in rat liver, kidney, lung, testis and brain. These data extend the insight that a subfamily of SDR isozymes, tissue-distinctively expressed, catalyzes the first step in RA biogenesis.