CLONING OF A CDNA FOR A 2ND RETINOL DEHYDROGENASE TYPE-II - EXPRESSION OF ITS MESSENGER-RNA RELATIVE TO TYPE-I

A retinol dehydrogenase, RoDH(I), which recognizes hole-cellular retin ol-binding protein (CRBP) as substrate, has been cloned, expressed, an d identified as a short-chain dehydrogenase/reductase (Chai, X., Boerm an, M. H. E. M., Zhai, Y., and Napoli, J. L. (1995) J. Biol. Chem. 270 , 3900-3904). This work reports the cloning and expression of a cDNA e ncoding a RoDH isozyme, RoDH(II). The predicted amino acid sequence ve rifies RoDH(II) as a short-chain dehydrogenase/reductase, 82% identica l with RoDH(I), RoDH(II) recognized the physiological form of retinol as substrate, CRBP, with a K-m of 2 mM. Similar to microsomal RoDH and RoDH(I), RoDH(II) had higher activity with NADP rather than NAD, was stimulated by ethanol and phosphatidyl choline, was not inhibited by t he medium chain alcohol dehydrogenase inhibitor 4-methylpyrazole, but was inhibited by phenylarsine oxide and the short-chain dehydrogenase/ reductase inhibitor carbenoxolone. Northern blot analysis detected RoD H(I) and RoDH(II) mRNA only in rat liver, but RNase protection assays revealed RoDH(I) and RoDH(II) mRNA in kidney, lung, testis, and brain. These data indicate that short-chain dehydrogenases/reductase isozyme s expressed tissue-distinctively catalyze the first step of retinoic a cid biogenesis from the physiologically most abundant substrate, CRBP.