Labrecque J, Dumas F, Lacroix A, Bhat P V
Laboratory of Nutrition and Cancer, Centre de Recherche Hôtel-Dieu de Montréal, Québec, Canada.
Biochem J. 1995 Jan 15;305 ( Pt 2)(Pt 2):681-4. doi: 10.1042/bj3050681.
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.
维甲酸受体（RAR）和类视黄醇X受体（RXR）。9-顺式维甲酸是RXR受体的特异性配体，而9-顺式维甲酸或全反式维甲酸均可激活RAR受体家族。RXR的存在表明异构化在维甲酸生物学中具有新的作用。我们在此报告在大鼠肾脏中鉴定出一种醛脱氢酶，它能高效地将9-顺式和全反式视黄醛氧化为相应的维甲酸，9-顺式视黄醛的活性比全反式视黄醛高2倍。基于氨基酸序列、最适pH值和水合氯醛抑制等多项标准，该酶被发现是醛脱氢酶的一种新型同工酶。在大鼠肾脏中鉴定出了9-顺式视黄醇，它是9-顺式视黄醛生物合成的前体。内源性9-顺式视黄醇的存在以及参与催化9-顺式视黄醛的特异性脱氢酶的存在表明，全反式视黄醇（类视黄醇）异构化为9-顺式视黄醇（类视黄醇）发生在视黄醇水平，类似于视觉循环中全反式视黄醇异构化为11-顺式视黄醇。
