CLONING OF A RAT CDNA-ENCODING RETINAL DEHYDROGENASE ISOZYME TYPE-I AND ITS EXPRESSION IN ESCHERICHIA-COLI

Peptides sequenced from the purified rat liver cytosolic retinal dehyd rogenase P1 [Posch, K.C., Burns, R.D. and Napoli, J.L., 1992. Biosynth esis of all-trans-retinoic acid from retinal: recognition of retinal b ound to cellular retinol-binding protein (type I) as substrate by a pu rified cytosolic dehydrogenase. J. Biol. Chem. 267, 19676-19682] were used to design oligonucleotides for cloning its cDNA. The deduced amin o acid sequence of P1, now designated retinal dehydrogenase type I or RalDH(I), has close similarity with mouse AHD-2 and rat kidney aldehyd e dehydrogenase, but is distinct from rat phenobarbital-inducible alde hyde dehydrogenase (PIADH), the presumed rat liver homolog of mouse AH D-2. Rat kidney (100%) and lung (88%) show relatively high mRNA levels of RalDH(I), liver (34%) and brain (22%) have moderate levels, and te stis (8%) has low levels. Retinoid status affects RalDH(I) mRNA levels differently in different tissues. E. coli-expressed RalDH(I) exhibits allosteric kinetics for retinal with a Hill coefficient of 1.7, a K-0 .5 value of 1.4 mu M and a V-max of 52 nmol min(-1) mg(-1) protein. Th ese data establish the cospecificity of P1 and RalDH(I), show that ret inoid status affects expression of its mRNA in a tissue-dependent mann er, and illustrate that aldehyde dehydrogenase isozymes with extensive homology can participate in different metabolic paths, e.g., RalDH vs . PIADH. (C) 1997 Elsevier Science B.V.