Isoelectric focusing studies of aldehyde dehydrogenases from mouse tissues: variant phenotypes of liver, stomach and testis isozymes

The so-called "testis-specific aldehyde dehydrogenase" corresponds to type 2 retinaldehyde dehydrogenase in the mouse

The distribution pattern of "testis-specific aldehyde dehydrogenase" in mouse tissues was investigated. Because of the broad substrate specificity and the high degree of sequence identity of the large aldehyde dehydrogenase family a specific detection of single isoforms is not possible by histochemical means. Therefore, the technique of native isoelectric focusing was used. Thus, the expression of four to five banded "testis-specific aldehyde dehydrogenase" in the mouse testis was confirmed. However, the activity of this enzyme with the same pattern of multiplicity was found not only in the testis but also in the uterus and in embryonic tissues. At 9.5 and 10.5 days of embryonic development the enzyme activity was restricted to tissues of the embryonic trunk and absent in extracts from cranial tissues. The tissue distribution as well as substrate specificity and isoelectric points indicate that the "testis-specific aldehyde dehydrogenase" corresponds to mouse type 2 retinaldehyde dehydrogenase.

Cloning of a rat cDNA encoding retinal dehydrogenase isozyme type I and its expression in E. coli

Peptides sequenced from the purified rat liver cytosolic retinal dehydrogenase P1 [Posch, K.C., Burns, R.D. and Napoli, J.L., 1992. Biosynthesis of all-trans-retinoic acid from retinal: recognition of retinal bound to cellular retinol-binding protein (type I) as substrate by a purified cytosolic dehydrogenase. J. Biol. Chem. 267, 19676-19682] were used to design oligonucleotides for cloning its cDNA. The deduced amino acid sequence of P1, now designated retinal dehydrogenase type I or RalDH(I), has close similarity with mouse AHD-2 and rat kidney aldehyde dehydrogenase, but is distinct from rat phenobarbital-inducible aldehyde dehydrogenase (PIADH), the presumed rat liver homolog of mouse AHD-2. Rat kidney (100%) and lung (88%) show relatively high mRNA levels of RalDH(I), liver (34%) and brain (22%) have moderate levels, and testis (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 K0.5 value of 1.4 microM and a Vmax of 52 nmol min(-1) mg(-1) protein. These data establish the cospecificity of P1 and RalDH(I), show that retinoid status affects expression of its mRNA in a tissue-dependent manner, and illustrate that aldehyde dehydrogenase isozymes with extensive homology can participate in different metabolic paths, e.g., RalDH vs. PIADH.

A novel isoenzyme of aldehyde dehydrogenase specifically involved in the biosynthesis of 9-cis and all-trans retinoic acid

The pleiotropic effects of retinoids are mediated by two families of nuclear receptors: RAR (retinoic acid receptors) and RXR (retinoid X receptors). 9-cis-Retinoic acid is a specific ligand for RXR receptors, whereas either 9-cis- or all-trans-retinoic acid activates the RAR receptor family. The existence of RXRs suggests a new role for isomerization in the biology of retinoic acid. We report here the identification of an aldehyde dehydrogenase in the rat kidney that catalysed the oxidation of 9-cis- and all-trans-retinal to corresponding retinoic acids with high efficiency, 9-cis-retinal being 2-fold more active than all-trans-retinal. Based on several criteria, such as amino acid sequence, pH optimum, and inhibition by chloral hydrate, this enzyme was found to be a novel isoenzyme of aldehyde dehydrogenase. 9-cis-Retinol, the precursor for the biosynthesis of 9-cis-retinal was identified in the rat kidney. The occurrence of endogenous 9-cis-retinol and the existence of specific dehydrogenase which participates in the catalysis of 9-cis-retinal suggest that all-trans-retinoi(d) isomerization to 9-cis-retinoi(d) occurs at the retinol level, analogous to all-trans-retinol isomerization to 11-cis-retinol in the visual cycle.