Gene/Protein Disease Symptom Drug Enzyme Compound
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Query: UNIPROT:Q8NEX9 (reductase)
 26,410 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

A retinol dehydrogenase, RoDH(1), which recognizes holo-cellular retinol-binding protein (CRBP) as substrate, has been cloned, expressed, and identified as a short-chain dehydrogenase/reductase (Chai, X., Boerman, 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 encoding a RoDH isozyme, RoDH(II). The predicted amino acid sequence verifies RoDH(II) as a short-chain dehydrogenase/reductase, 82% identical with RoDH(I). RoDH(II) recognized the physiological form of retinol as substrate, CRBP, with a Km 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 the 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 RoDH(I) and RoDH(II) mRNA only in rat liver, but RNase protection assays revealed RoDH(I) and RoHD(II) mRNA in kidney, lung, testis, and brain. These data indicate that short-chain dehydrogenases/reductase isozymes expressed tissue-distinctively catalyze the first step of retinoic acid biogenesis from the physiologically most abundant substrate, CRBP.
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PMID:Cloning of a cDNA for a second retinol dehydrogenase type II. Expression of its mRNA relative to type I. 749 45

Rabbit liver cytosol exhibits very high retinol dehydrogenase activity. At least two retinol dehydrogenases were demonstrated to exist in rabbit liver cytosol, and the major one, a cytosolic NADP(H)-dependent retinol dehydrogenase (systematic name: retinol oxidoreductase) was purified about 1795-fold to electrophoretic and column chromatographic homogeneity by a procedure involving column chromatography on AF-Red Toyopearl twice and then hydroxyapatite. Its molecular mass was estimated to be 34 kDa by SDS-PAGE, and 144 kDa by HPLC gel filtration, suggesting that it is a homo-tetramer. The enzyme uses free retinol and retinal, and their complexes with CRBP as substrates in vitro. The optimum pH values for retinol oxidation of free retinol and CRBP-retinol were 8.8-9.2 and 8.0-9.0, respectively, and those for retinal reduction of free retinal and retinal-CRBP were the same, 7.0-7.6. Km for free retinol and Vmax for retinal formation were 2.8 microM and 2893 nmol/min per mg protein at 37 degrees C (pH 9.0) and the corresponding values with retinol-CRBP as a substrate were 2.5 microM and 2428 nmol/min per mg protein at 37 degrees C (pH 8.6); Km for free retinal and Vmax for retinol formation were 6.5 microM and 4108 nmol/min per mg protein, and the corresponding values with retinal-CRBP as a substrate were 5.1 microM and 3067 nmol/min per mg protein at 37 degrees C, pH 7.4. NAD(H) was not effective as a cofactor. 4-Methylpyrazole was a weak inhibitor (IC50 = 28 mM) of the enzyme, and ethanol was neither a substrate nor an inhibitor of the enzyme. This enzyme exhibits relatively broad aldehyde reductase activity and some ketone reductase activity, the activity for aromatic substitutive aldehydes being especially high and effective. Whereas, except in the case of retinol, oxidative activity toward the corresponding alcohols was not detected. This novel cytosolic enzyme may play an important role in vivo in maintaining the homeostasis of retinal, the substrate of retinoic acid synthesis, at least in rabbit liver, since a high concentration of retinol in liver and the lower Km of the enzyme for retinol force the oxidative reaction, while higher activity of retinal reductase at physiological pH forces the reductive reaction.
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PMID:Purification and characterization of a novel cytosolic NADP(H)-dependent retinol oxidoreductase from rabbit liver. 907 15

The ligand-controlled retinoic acid (RA) receptors and retinoid X receptors are important for several physiological processes, including normal embryonic development, but little is known about how their ligands, all-trans and 9-cis RA, are generated. Here we report the identification of a stereo-specific 9-cis retinol dehydrogenase, which is abundantly expressed in embryonic tissues known to be targets in the retinoid signaling pathway. The membrane-bound enzyme is a member of the short-chain alcohol dehydrogenase/reductase superfamily, able to oxidize 9-cis retinol into 9-cis retinaldehyde, an intermediate in 9-cis RA biosynthesis. Analysis by nonradioactive in situ hybridization in mouse embryos shows that expression of the enzyme is temporally and spatially well controlled during embryogenesis with prominent expression in parts of the developing central nervous system, sensory organs, somites and myotomes, and several tissues of endodermal origin. The identification of this enzyme reveals a pathway in RA biosynthesis, where 9-cis retinol is generated for subsequent oxidation to 9-cis RA.
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PMID:The identification of a 9-cis retinol dehydrogenase in the mouse embryo reveals a pathway for synthesis of 9-cis retinoic acid. 953 49

Dihydrotestosterone (DHT) is the most potent naturally occurring androgen, and its production in the testis may have important consequences in developmental and reproductive processes. In the rat testis, three factors can contribute to intracellular DHT levels: 1) synthesis of DHT from T by 5alpha-reductase, 2) conversion of DHT to 5alpha-androstane-3alpha, 17beta-diol (3alpha-DIOL) by the reductive activity of 3alpha-hydroxysteroid dehydrogenase (3alpha-HSD), and 3) conversion of 3alpha-DIOL by an oxidative 3alpha-HSD activity. While the type I 3alpha-HSD enzyme (3alpha-HSD1 or AKR1C9) is an oxidoreductase in vitro and could theoretically be responsible for factors 2 and 3, we have shown previously that rat Leydig cells have two 3alpha-HSD activities: a cytosolic NADP(H)- dependent activity, characteristic of 3alpha-HSD1, and a microsomal NAD(H)-dependent activity. The two activities were separable by both developmental and biochemical criteria, but the identity of the second enzyme was unknown. To identify the microsomal NAD(H)-dependent 3alpha-HSD in rat Leydig cells, degenerate primers were used to amplify a number of short-chain alcohol dehydrogenases. Sequence analysis of cloned PCR products identified retinol dehydrogenase type II (RoDH2) as the prevalent species in purified Leydig cells. RoDH2 cDNA was subcloned into expression vectors and transiently transfected into CHOP and COS-1 cells. Its properties were compared with transiently transfected 3alpha-HSD1. When measured in intact CHOP and COS-1 cells, RoDH2 cDNA produced a protein that catalyzed the conversions of 3alpha-DIOL to DHT and androsterone to androstanedione, but not the reverse reactions. Therefore, the 3alpha-HSD activity of RoDH2 was exclusively oxidative. In contrast, type I 3alpha-HSD cDNA produced a protein that was exclusively a 3alpha-HSD reductase. In cell homogenates and subcellular fractions, RoDH2 catalyzed both 3alpha-HSD oxidation and reduction reactions that were NAD(H) dependent, and the enzyme activities were located in the microsomes. Type I 3alpha-HSD also catalyzed both oxidation and reduction, but was located in the cytosol and was NADP(H) dependent. We conclude that type I 3alpha-HSD and RoDH2 have distinct 3alpha-HSD activities with opposing catalytic directions, thereby controlling the rates of DHT production by Leydig cells.
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PMID:Identification of the oxidative 3alpha-hydroxysteroid dehydrogenase activity of rat Leydig cells as type II retinol dehydrogenase. 1080 68

17beta-Hydroxysteroid dehydrogenases (17beta-HSDs) regulate androgen and estrogen concentrations in mammals. By 1995, four distinct enzymes with 17beta-HSD activity had been identified--17beta-HSD-types 1 and 3, which, in vivo, are NADPH-dependent reductases; and 17beta-HSD-types 2 and 4, which, in vivo, are NAD(+)-dependent oxidases. Since then, six additional enzymes with 17beta-HSD activity have been isolated from mammals. With the exception of 17beta-HSD-type 5, which belongs to the aldoketo-reductase (AKR) family, these 17beta-HSDs belong to the short chain dehydrogenase/reductase (SDR) family. Several 17beta-HSDs appear to be examples of convergent evolution. That is, 17beta-HSD activity arose several times from different ancestors. Some 17beta-HSDs share a common ancestor with retinoid oxido-reductases and have retinol dehydrogenase activity. 17beta-HSD-types 2, 6 and 9 appear to have diverged from ancestral retinoid dehydrogenases early in the evolution of deuterostomes during the Cambrian, about 540 million years ago. This coincided with the origin of nuclear receptors for androgens and estrogens suggesting that expression of 17beta-HSDs had an important role in the early evolution of the physiological response to androgens and estrogens.
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PMID:Evolution of 17beta-hydroxysteroid dehydrogenases and their role in androgen, estrogen and retinoid action. 1116 32

Retinoids are chromophores involved in vision, transcriptional regulation, and cellular differentiation. Members of the short chain alcohol dehydrogenase/reductase superfamily catalyze the transformation of retinol to retinal. Here, we describe the identification and properties of three enzymes from a novel subfamily of four retinol dehydrogenases (RDH11-14) that display dual-substrate specificity, uniquely metabolizing all-trans- and cis-retinols with C(15) pro-R specificity. RDH11-14 could be involved in the first step of all-trans- and 9-cis-retinoic acid production in many tissues. RDH11-14 fill the gap in our understanding of 11-cis-retinal and all-trans-retinal transformations in photoreceptor (RDH12) and retinal pigment epithelial cells (RDH11). The dual-substrate specificity of RDH11 explains the minor phenotype associated with mutations in 11-cis-retinol dehydrogenase (RDH5) causing fundus albipunctatus in humans and engineered mice lacking RDH5. Furthermore, photoreceptor RDH12 could be involved in the production of 11-cis-retinal from 11-cis-retinol during regeneration of the cone visual pigments. These newly identified enzymes add new elements to important retinoid metabolic pathways that have not been explained by previous genetic and biochemical studies.
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PMID:Dual-substrate specificity short chain retinol dehydrogenases from the vertebrate retina. 1222 7

Human alcohol dehydrogenase (ADH) constitutes a complex family. Class IV ADH (ADH4) is characteristic in its epithelial expression in the aerodigestive tract and high V(max) and K(m) for oxidation of ethanol. ADH4 exhibits the highest catalytic efficiency for retinol oxidation in human ADH family. Initial velocity, product inhibition, and dead-end inhibition studies indicate that ADH4, when functioning as ethanol dehydrogenase, conforms to an ordered sequential mechanism with coenzyme binding first and releasing last in catalytic cycle. When functioning as retinol dehydrogenase, the mechanism of ADH4 deduced from steady-state kinetic and equilibrium-binding studies is best described as a rapid equilibrium random mechanism with two dead-end ternary complex for retinol oxidation and a rapid equilibrium ordered mechanism with one dead-end ternary complex for retinal reduction, a unique mechanistic form for zinc-containing ADHs in the medium chain dehydrogenase/reductase superfamily. Kinetic and genetic studies support the proposal that ADH4 may play two important physiological roles, i.e., as a major contributor to first-pass metabolism of ethanol in stomach as well as involvement in the synthesis of retinoic acid, a hormonal ligand controlling a nuclear receptor signaling pathway that regulates growth, development, and epithelial maintenance. Quantitative simulation studies indicate that retinol metabolism through ADH pathway can be inhibited to a significant extent during alcohol consumption. The perturbation of retinoic acid synthesis by ethanol may underlie the pathogenesis of fetal alcohol syndrome and alcohol-related upper digestive tract cancer.
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PMID:Human class IV alcohol dehydrogenase: kinetic mechanism, functional roles and medical relevance. 1260 7

In this study, we isolated a cDNA for tetrameric carbonyl reductase (CR) from pig heart. The pig CR showed high amino acid sequence identity (81%) with rabbit NADP(+)-dependent retinol dehydrogenase (NDRD). The purified recombinant pig CR and NDRD were about 100-kDa homotetramers and exhibited high reductase activity towards alkyl phenyl ketones, alpha-dicarbonyl compounds and all-trans-retinal. The identity of NDRD with the tetrameric CR was verified by protein sequencing of CR purified from rabbit heart. Both tetrameric CR and its mRNA were ubiquitously expressed in pig and rabbit tissues. The pig and rabbit enzymes belonged to the short-chain dehydrogenase/reductase family, and their sequences comprise a C-terminal SRL tripeptide, which is a variant of the type 1 peroxisomal targeting signal, SKL. Transfection of HeLa cells with vectors expressing pig CR demonstrated that the enzyme is localized in the peroxisomes. Thus, the tetrameric form of CR represents the first mammalian peroxisomal enzyme that reduces all-trans-retinal as the endogenous substrate.
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PMID:Cloning, expression and tissue distribution of a tetrameric form of pig carbonyl reductase. 1260 22

The biological functions of vitamin A in the epidermis are mediated by all-trans retinoic acid, which is biosynthesized from retinol in two oxidative reactions. The first step involves enzymatic conversion of retinol to retinaldehyde. The physiological significance and relative contributions of the various retinol dehydrogenases to the oxidation of retinol in epidermal cells remain unclear. We report the characterization of a retinol dehydrogenase/reductase of the SDR superfamily, hRoDH-E2, which is abundantly expressed in the epidermis, epidermal appendages and in cultured epidermal keratinocytes. Both in live keratinocytes and in isolated keratinocyte microsomes, where the enzyme normally localizes, hRoDH-E2 functions as a bona fide retinol dehydrogenase. In the prevailing oxidative reaction it recognizes both free- and CRBP-bound retinol, and shows preference toward NADP as a co-substrate. In comparison, hRoDH-E2 retinol dehydrogenase activity in the simple epithelial HEK 293 cells is much lower and in CHO cells is non-existent. hRoDH-E2 transcripts are distributed throughout the epidermal layers but are more abundant in the basal cells. In contrast, the protein is detected predominantly in the basal and the most differentiated living layers. Its synthesis is negatively regulated by retinoic acid. The biochemical properties and the differential expression of hRoDH-E2 in the strata where retinoic acid signaling is critical for epidermal homeostasis support a conclusion that hRoDH-E2 bears the characteristics of the major microsomal retinol dehydrogenase activity in the epidermal keratinocytes in physiological circumstances.
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PMID:Expression pattern and biochemical characteristics of a major epidermal retinol dehydrogenase. 1261 84

Human aldo-keto reductases (AKRs) of the AKR1C subfamily function in vitro as 3-keto-, 17-keto-, and 20-ketosteroid reductases or as 3alpha-, 17beta-, and 20alpha-hydroxysteroid oxidases. These AKRs can convert potent sex hormones (androgens, estrogens, and progestins) into their cognate inactive metabolites or vice versa. By controlling local ligand concentration AKRs may regulate steroid hormone action at the prereceptor level. AKR1C2 is expressed in prostate, and in vitro it will catalyze the nicotinamide adenine dinucleotide (NAD(+))-dependent oxidation of 3alpha-androstanediol (3alpha-diol) to 5alpha-dihydrotestosterone (5alpha-DHT). This reaction is potently inhibited by reduced NAD phosphate (NADPH), indicating that the NAD(+): NADPH ratio in cells will determine whether AKR1C2 makes 5alpha-DHT. In transient COS-1-AKR1C2 and in stable PC-3-AKR1C2 transfectants, 5alpha-DHT was reduced by AKR1C2. However, the transfected AKR1C2 oxidase activity was insufficient to surmount the endogenous 17beta-hydroxysteroid dehydrogenase (17beta-HSD) activity, which eliminated 3alpha-diol as androsterone. PC-3 cells expressed retinol dehydrogenase/3alpha-HSD and 11-cis-retinol dehydrogenase, but these endogenous enzymes did not oxidize 3alpha-diol to 5alpha-DHT. In stable LNCaP-AKR1C2 transfectants, AKR1C2 did not alter androgen metabolism due to a high rate of glucuronidation. In primary cultures of epithelial cells, high levels of AKR1C2 transcripts were detected in prostate cancer, but not in cells from normal prostate. Thus, in prostate cells AKR1C2 acts as a 3-ketosteroid reductase to eliminate 5alpha-DHT and prevents activation of the androgen receptor. AKR1C2 does not act as an oxidase due to either potent product inhibition by NADPH or because it cannot surmount the oxidative 17beta-HSD present. Neither AKR1C2, retinol dehydrogenase/3alpha-HSD nor 11-cis-retinol dehydrogenase is a source of 5alpha-DHT in PC-3 cells.
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PMID:Human type 3 3alpha-hydroxysteroid dehydrogenase (aldo-keto reductase 1C2) and androgen metabolism in prostate cells. 1281 May 47


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