Search PubMed⌕ Search

SEARCH · Search PubMed

Results for “Retinaldehyde”

Search indexed PubMed citations on genomics, clinical trials, systematic reviews and public health. Explore titles, authors and supplied subject terms, then open the PubMed record.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 559 records · Page 31Linked to original sources
PubMed2004

Primary events in dim light vision: a chemical and spectroscopic approach toward understanding protein/chromophore interactions in rhodopsin.

The visual pigment rhodopsin (bovine) is a 40 kDa protein consisting of 348 amino acids, and is a prototypical member of the subfamily A of G protein-coupled receptors (GPCRs). This remarkably efficient light-activated protein (quantum yield = 0.67) binds the chromophore 11-cis-retinal covalently by attachment to Lys296 through a protonated Schiff base. The 11-cis geometry of the retinylidene chromophore keeps the partially active opsin protein locked in its inactive state (inverse agonist). Several retinal analogs with defined configurations and stereochemistry have been incorporated into the apoprotein to give rhodopsin analogs. These incorporation results along with the spectroscopic properties of the rhodopsin analogs clarify the mode of entry of the chromophore into the apoprotein and the biologically relevant conformation of the chromophore in the rhodopsin binding site. In addition, difference UV, CD, and photoaffinity labeling studies with a 3-diazo-4-oxo analog of 11-cis-retinal have been used to chart the movement of the retinylidene chromophore through the various intermediate stages of visual transduction.

Animals↗
PubMed1993

Prostaglandin E and 12-O-tetradecanoylphorbol-13-acetate are negative modulators of retinoic acid synthesis.

Although retinoic acid is an important modulator of gene transcription that affects diverse processes during embryonic development and in the adult, no regulators of retinoic acid synthesis have been identified. This work will show that deletion of prostaglandin E1 (PGE1) from the defined medium of confluent Madin-Darby canine kidney (MDCK) cells increased retinoic acid synthesis from retinol as much as twofold. Omitting any one of the other four growth factors (cortisol, insulin, transferrin, triiodothyronine) had no effect. Adding PGE1 to confluent cells maintained in its absence caused 71 +/- 17% (mean +/- SE, 10 experiments) inhibition of the conversion of retinol into retinoic acid. The ED50 of PGE1 was 70 nM and a maximum effect was observed by 1.5 h. 12-O-Tetradecanoylphorbol-13- acetate (TPA), an inducer of PGE synthesis in MDCK cells, decreased retinoic acid synthesis by 73 +/- 14% (mean +/- SE, 10 experiments). The ED50 of TPA was 5 nM and at least 4 h were required for a maximum effect. TPA inhibited the first and rate-limiting step, the conversion of retinol into retinal, and did not decrease either the conversion of retinal into retinoic acid or the elimination t1/2 of retinoic acid. PGE1 and TPA did not inhibit retinoic acid synthesis completely, nor were their actions additive or synergistic, consistent with more than one pathway of retinoic acid synthesis. Indomethacin did not prevent the TPA effect, suggesting that TPA acts independently of prostaglandin generation. MDCK cells expressed mRNA for retinoic acid receptor-alpha and retinoic acid receptor-beta constitutively, and neither was induced by retinoic acid, consistent with an advanced state of differentiation. These data identify two antagonists of retinoid action, TPA and PGE, as modulators of retinoic acid synthesis in a retinoic acid-responsive cell. They also demonstrate the utility of MDCK cells for studying interactions among retinoic acid synthesis, the mechanism(s) of retinoic acid action, and the effects of TPA on retinoic acid synthesis and action.

Alprostadil↗
PubMed1995

Effects of sulfhydryl reagents, retinoids, and solubilization on the activity of microsomal retinol dehydrogenase.

A microsomal retinol dehydrogenase (RoDH) that recognizes holo-cellular retinol binding protein (CRBP) as substrate is inhibited by phenylarsine oxide (IC50 = 3 microM) in the presence of 10 mM cysteine. Inhibition was reversible with dithiothreitol, indicating that two cysteine residues in close proximity are essential for RoDH activity. Bromophenylarsine oxide was an irreversible inhibitor (IC50 = 0.2 microM), suggesting that a nucleophile lies close to the two cysteine residues. N-Ethylmaleimide inhibited reactions supported by holo-CRBP, but not from free retinol, suggesting that it obstructed holo-CRBP access to RoDH without affecting the catalytic site. RoDH activity was similar in microsomes from vitamin A-sufficient or vitamin A-deficient rats and was not inhibited by relatively high concentrations (5 microM) of all-trans-retinoic acid, holo-cellular retinoic acid binding protein, apo-cellular retinoic acid binding protein, or 9-cis-retinoic acid. Triton X-100 stimulated RoDH activity eightfold at a detergent to protein ratio of 0.25 to 1 (w/w). A combination of Tween 80, Brij 92, and Triton X-100 (2:1:2) stimulated RoDH activity eightfold at a detergent to protein ratio of 2.5 to 1 (w/w). Detergent-solubilized RoDH, partially purified through a PAO-Sepharose resin, preferred NADP(H) as cofactor, had a Km for retinal synthesis from holo-CRBP of 0.6 microM (Vmax = 115 pmol/min/mg protein) and a Km for reduction of retinal bound to CRBP of 0.6 microM (Vmax = 613 pmol/min/mg protein). This work provides further insight into microsomal RoDH and strengthens the evidence of an interaction between RoDH and holo-CRBP.

Alcohol Oxidoreductases↗
PubMed1996

Stoichiometric conversion of all trans-beta-carotene to retinal by pig intestinal extract.

beta-Carotene and other provitamin A carotenoids are major dietary sources of vitamin A for humans and for many animals throughout the world. Two pathways for this oxidative reaction in mammals are: (1) central cleavage by beta-carotene 15,15'-dioxygenase (EC 1.13.11.21) to yield two molecules of retinal per molecule of beta-carotene consumed and (2) eccentric (or random) cleavage via several beta-apo carotenals to yield one molecule of retinal and various smaller fragments per molecule of beta-carotene oxidized. By the use of improved methods to minimize nonenzymatic reactions and to measure isomers of retinal, the mean experimentally measured molar ratio of retinal formed to beta-carotene consumed by pig intestinal preparations (800 and 10,000g supernatants) was 1.88 +/- 0.08, close to the theoretical value of 2.0 for central cleavage. beta-Apo carotenals, retinol, and retinoic acid were detected, if at all, in trace amounts during incubation. Thus, preparations of pig intestinal mucosa, which is considered a good physiologic model for human intestine, clearly convert beta-carotene to retinal, in large part if not solely, by central cleavage. Whether eccentric cleavage plays a greater role in vivo than it does in vitro is still uncertain.

Animals↗
PubMed1997

Antioxidant reactions of all-trans retinol in phospholipid bilayers: effect of oxygen partial pressure, radical fluxes, and retinol concentration.

Lipoperoxyl radical-scavenging activity of retinol in unilamellar soybean phosphatidylcholine liposomes was studied under a variety of conditions to appreciate to what extend retinol may be considered an effective antioxidant. Peroxidation, initiated by 2 mM 2,2'-azobis(amidino-propane)hydrochloride (AAPH), was carried out at 160 torr O2 or at 15 torr O2, in the absence or in the presence of 10 to 40 mM retinol. As evaluated by the length of the inhibition periods, t(inh), and by the ratio between the inhibition and propagation rate, R(inh)/R(p), the antioxidant activity of retinol was higher at 15 torr O2 than at 160 torr O2. The consumption rate of retinol was markedly faster at 160 torr O2 than at 15 torr O2 and increased with the increase of retinol concentration under both oxygen tensions. When liposome peroxidation was carried out under N2, retinol consumption was independent of retinol concentration. Peroxyl radicals oxidize retinol to 5,6-retinol epoxide. The ratio between 5,6-epoxide formed and the retinol consumed was markedly higher at 15 torr O2 than under air and decreased with the increased retinol concentrations. When butylated hydroxytoluene was included into the liposomal suspension, most of the consumed retinol was converted into 5,6-epoxide. Liposomes were incubated at 15 torr O2, in the presence of 0.5 to 10 mM AAPH. The antioxidant effectiveness of 40 mM retinol, as measured by the R(inh)/R(p) ratio, increased with the increase of the radical fluxes. The results suggest, besides radical trapping, that a major consumption of retinol during lipid oxidation occurs through self-oxidation reactions, which are concentration- and oxygen-dependent. A decreased self-oxidation makes retinol a better lipoperoxyl radical scavenger at low, rather than at high partial pressure of oxygen. However, when self-oxidation of retinol is prevented, only a minor fraction of the antioxidant is allowed to effectively act as a radical scavenger, suggesting that the radical-trapping reactions are rate-limiting for the antioxidant process. Peroxyl radical concentration, by shifting the route of the retinol activity toward radical scavenging, brings about an increasingly more efficient radical trapping. It is concluded that all-trans retinol behaves as a more effective antioxidant at low oxygen partial pressure, low retinol concentrations, and high radical flux.

Antioxidants↗
PubMed1998

Characterization of the cytochrome P450 CYP2J4: expression in rat small intestine and role in retinoic acid biotransformation from retinal.

The sites of expression in the small intestine and the function of CYP2J4, a recently identified rat cytochrome (P450) isoform found to be predominantly expressed in the small intestine, were characterized. Immunoblot analysis with a polyclonal antibody to heterologously expressed CYP2J4 revealed that expression of CYP2J4 was at the highest level in the distal duodenum and jejunum and decreased toward the ileum. Villous cells expressed higher levels of CYP2J4 than crypt cells. Isoform-specific RNA polymerase chain reaction indicated that a related P450 isoform, CYP2J3, was only a minor form in rat small intestine. Since the intestinal mucosa is exposed to high levels of dietary nutrients, we hypothesized that CYP2J4 may be active toward diet-derived factors. We determined that purified, heterologously expressed CYP2J4 is active toward all-trans- and 9-cis-retinal in reconstituted systems, producing the corresponding retinoic acids as the major products. Apparent K(m) values for the formation of retinoic acids were 54 and 49 microM, respectively, and apparent Vmax values were 20 and 21 nmol/min/nmol P450, respectively. These activities were readily inhibited by a polyclonal anti-CYP2J4 antibody. Rat enterocyte microsomes were also active with all-trans-retinal to produce all-trans-retinoic acid in the presence of NADPH, and the majority of retinoic acid synthesis activity was inhibited by the polyclonal anti-CYP2J4 antibody. These findings suggest that CYP2J4 plays a major role in intestinal microsomal metabolism of retinal to retinoic acid and may be involved in the maintenance of retinoid homeostasis in the small intestine in vivo.

Animals↗
PubMed2001

Standard apparent reduction potentials for biochemical half reactions as a function of pH and ionic strength.

Standard apparent reduction potentials are important because they give a more global view of the driving forces for redox reactions than do the standard transformed Gibbs energies of formation of the reactants. This paper emphasizes the effects of pH on biochemical half reactions in the range pH 5 to 9, but it also shows the effect of ionic strength. These effects can be calculated if the pKs of acid groups in the reactants are known in the range pH 4 to 10. Raising the pH decreases the standard apparent reduction potentials of half reactions when it has an effect, and the slope is proportional to minus one times the ratio of the change in binding of hydrogen ions in the half reaction to the number of electrons transferred. These effects are discussed for 19 biochemical reactions. This effect is most striking for the nitrogenase reaction, where the apparent equilibrium constant is proportional to 10(-10 pH) and is unfavorable for nitrogen fixation above pH 8.

Acetone↗
PubMed1996

Assay of beta-carotene 15,15'-dioxygenase activity by reverse-phase high-pressure liquid chromatography.

beta-Carotene 15,15'-dioxygenase catalyzes the conversion of beta-carotene into two molecules of retinal. Although this enzyme reaction is the first step in providing animals with vitamin A, there is little knowledge about its regulation in mammals. In order to facilitate studies on this enzyme, we have developed a rapid and simple assay method for the measurement of retinal formation by beta-carotene dioxygenase. All-trans-beta-carotene solubilized in aqueous solution with Tween 40 was incubated with an enzyme preparation of rat tissue at 37 degrees C for 30 min. Then, the reaction was stopped with a formaldehyde treatment followed by addition of acetonitrile. After centrifugation, the supernatant was directly subjected to high-pressure liquid chromatographic analysis of retinal. This assay method did not involve any vigorous extraction or concentration procedure. All-trans- and 13-cis-retinals, major geometric isomers found in the reaction mixture, were coeluted at 7.5 min, but they were well separated from other possible metabolites of beta-carotene such as retinoic acid, retinol, and apocarotenals. Moreover, the recovery of retinal reached more than 93% and the detection limit of standard retinal was 0.2 pmol/0.2 ml of reaction mixture. Enzyme activities of rat tissues were 694, 180, 16, 8, and approx 1 pmol retinal/mg protein/h in the intestine, liver, brain, lung, and kidney homogenates, respectively.

Animals↗
PubMed1997

Macroscopic orientation of natural and model membranes for structural studies.

One approach for obtaining high-resolution structural and functional information for biomembranes and their proteins is by static solid-state NMR of oriented systems. Here, a general procedure to align fully functional biological membranes containing large membrane proteins (Mr >30,000) is described. The method, based on the isopotential spin-dry ultracentrifugation technique, relies on the centrifugation of membrane fragments onto a support with simultaneous, or subsequent, partial evaporation of the solvent which aids alignment. The quality of orientation, as shown by the mosaic spread of the samples, was monitored by static solid-state 31P NMR for the phospholipids and by 2H NMR for a deuterated retinal in bovine rhodopsin. The generality of this method is demonstrated with three different membranes containing bovine rhodopsin in reconstituted bilayers, natural membranes with the red cell anion exchange transport protein in erythrocytes, band 3, and the nicotinic acetylcholine receptor.

Animals↗
PubMed1999

Analysis of cyclic and acyclic analogs of retinol, retinoic acid, and retinal by laser desorption ionization-, matrix-assisted laser desorption ionization-mass spectrometry, and UV/Vis spectroscopy.

Laser desorption ionization (LDI)- and matrix-assisted laser desorption ionization (MALDI)-mass spectrometry (LDI-MS, MALDI-MS) at 337-nm laser wavelength were used to analyze retinol (vitamin A), retinoic acid, and retinal and their analogs 3-hydroxyretinol, 3-hydroxyretinoic acid, 3-hydroxyretinal, 4-oxoretinol, 4-oxoretinoic acid, 4-oxoretinal, 3,4-didehydroretinol (vitamin A(2)), 3,4-didehydroretinoic acid, 3,4-didehydroretinal, acycloretinol, acycloretinoic acid, and acycloretinal. The compounds exhibit sufficient ionizability which allows to obtain mass spectra by LDI which are similar in quality to those obtained by MALDI. Mass spectra were recorded with a linear time-of-flight (TOF) instrument or a reflectron-type (RETOF) instrument in positive-ion mode. Under the conditions of LDI-MS the compounds form abundant radical molecular ions (M+*), whereas in the MALDI mass spectra abundant protonated molecular ions ([M + H]+) are observed. Characteristic fragment ions provide additional structural information. High-performance liquid chromatography (HPLC) coupled with UV/Vis photodiode detection was used to assist in retinoid characterization. Synthesis of 3-hydroxyretinal, 4-oxoretinal, and acycloretinal was performed by oxidative cleavage of the all-trans-carotenoids of zeaxanthin, canthaxanthin, and lycopene.

Molecular Structure↗
PubMed1994

Two different enzymes are primarily responsible for retinoic acid synthesis in rabbit liver cytosol.

Retinoic acid biosynthesis in rabbit liver was catalyzed by cytosolic NAD(+)-dependent dehydrogenase and oxygen-dependent oxidase, with an activity ratio of 59% and 41% in the presence of 2 mM dithiothreitol under aerobic conditions. The two enzymes could be well separated by fractionation involving ammonium sulfate precipitation. Purification of the enzymes indicated that the oxygen-dependent enzyme was a flavoenzyme, retinal oxidase (EC 1.2.3.11), composed of two 135 kDa subunits; and the NAD(+)-dependent enzyme was a basic pI retinal dehydrogenase composed of four 55-kDa subunits. A high concentration (1-2 mM) of DTT was required to stabilize the activity of retinal dehydrogenase during the purification procedures and storage, but inhibited the activity of retinal oxidase by 13-38%. The physiological roles of the two retinoic acid synthases in liver cytosol were discussed.

Aerobiosis↗
PubMed1998

Retinal identification in Pelvetia fastigiata.

Unidirectional blue light directs the rhizoid-thallus axis in the apolar zygote of the brown alga Pelvetia fastigiata. This effect is mediated by an increase in the intracellular concentration of cGMP. Here, we show the extraction, purification and identification of 1 microgram of all-trans retinal from 1.2 x 10(6) Pelvetia zygotes. The number of retinal molecules per cell was about 4 x 10(9). Since retinal, wherever present, is exclusively associated with an opsin to form a light sensitive complex (rhodopsin-like proteins), and since the physiological response originated by this protein produces a variation of cGMP concentration, this new finding suggests that a rhodopsin-like protein could be the photoreceptor in this brown alga.

Chromatography, High Pressure Liquid↗
PubMed1998

Characterization of beta-carotene 15,15'-dioxygenase activity in TC7 clone of human intestinal cell line Caco-2.

The purpose of this study was to identify mammalian cell line(s) which possess intrinsic enzymatic activity of beta-carotene 15, 15'-dioxygenase. This enzyme (EC1.13.11.21) converts beta-carotene to retinal (precursor of retinol and retinoic acid). To assess activity, cellular enzyme preparations were incubated with beta-carotene for 60 min; retinal formed was quantified by HPLC. Activity was not detected in IPEC-1, HepG2, HL60, Wurzburg, or parent Caco-2 cell lines. However, two subclones of Caco-2, PF11 and TC7, possessed activity (2.5 and 14.7 pmol/h.mg, respectively). Using the enzyme preparation of TC7 cells, retinal formation was linear with incubation time and protein concentration; Km and Vm values were 1.6 microM and 23.8 pmol/h.mg, respectively. In addition, when TC7 cells were maintained in serum-free medium, activity was increased 8.2-fold after 19 days of postconfluency. Finally, 48 h incubation with beta-carotene (delivered to TC7 cells in Tween 40) resulted in a 1.7-fold increase of dioxygenase activity and the appearance of vitamin A (9.3 pmol/mg protein). However, retinoic acid was not detected under our experimental conditions. In sum, the TC7 subclone of the Caco-2 cell line possesses beta-carotene 15, 15'-dioxygenase activity and thus can be useful in future investigations of human carotenoid metabolism.

Caco-2 Cells↗
PubMed1999

Retinoic acid biosynthetic activity and retinoid receptors in the olfactory mucosa of adult mice.

Retinoids play important roles in the ontogenic development of the olfactory system in mammals, but their function in adult olfactory mucosa has not been explored. In the present study, the olfactory mucosal expression of nuclear retinoid receptors was examined in adult mice. Several retinoic acid receptor isotypes were identified in olfactory mucosa from adult C57BL/6 mice by RNA-PCR and DNA sequence analysis, including RARbeta, RXRalpha, RXRbeta, and RXRgamma. In addition, a previously unidentified mouse RXRbeta isoform containing a 12-nucleotide insertion in exon 7 was detected. Furthermore, in vitro metabolic studies demonstrated that olfactory mucosal cytosolic and microsomal preparations are active in the biosynthesis of retinoic acids from all-trans- and 9-cis-retinal. These results indicate that components of the retinoid signal transduction system are expressed in adult olfactory mucosa and may play important roles in gene regulation in this unique tissue where olfactory neuronal cells are continuously replaced.

Amino Acid Sequence↗
PubMed2000

Reducing agents and light break an S-S bond activating rhodopsin in vivo in Chlamydomonas.

Light induces retinal synthesis via photoactivation of a small amount of Chlamydomonas rhodopsin pigment (Foster et al., Proc. Natl. Acad. Sci. USA 85, 6379-6383). A reducing agent [dithiothreitol (DDT) or mercaptoacetic acid (MAA)] also induces retinal synthesis in the dark via a rhodopsin with a chromophore. If the opsin is saturated with retinal and is bleached with light in the presence of a thiol trapping agent, the bleaching becomes irreversible. We conclude that the reducing agent as well as light break a disulfide bond resulting in activation of the rhodopsin and induction of carotenogenesis. Both the chemical and light induction is inhibited by GDPbetaS and pertussis toxin. Breaking the bridge between the 3rd and 5th helix may lead to increased proton accessibility of Asp134 leading to the rolling of the 3rd helix and MetaIIb formation.

Animals↗
PubMed2001

Time-resolved FT-IR spectroscopic investigation of the pH-dependent proton transfer reactions in the E194Q mutant of bacteriorhodopsin.

The photoreaction of the E194Q mutant of bacteriorhodopsin has been investigated at various pH values by time-resolved step-scan Fourier-transform infrared difference spectroscopy employing the attenuated total reflection technique. The difference spectrum at pH 8.4 is comparable to the N-BR difference spectra of the wild type with the remarkable exception that D85 is deprotonated. Since the retinal configuration is not perturbed by the E194Q mutation, it is concluded that there is no interaction of D85 with retinal during the lifetime of the N state. At pH 6, a consecutive state to the O intermediate is detected in which D212 is transiently protonated. The comparison with wild-type bacteriorhodopsin reveals that protonation of D212 represents an intermediate step during proton transfer from D85 to the proton release group in the final stage of the reaction cycle. The described effects are more pronounced in the E194Q mutant than in the E204Q mutant demonstrating different roles of these two glutamates/glutamic acids at least in the final stages of the catalytic cycle of bacteriorhodopsin.

Acids↗
PubMed2001

Metabolism of vitamin A affected by prostaglandin F synthase in contractile interstitial cells of bovine lung.

Contractile interstitial cells (CIC), the major component of the alveolar septum of the bovine lung are enriched in prostaglandin (PG) F synthase (Fukui, M., Fujimoto, T., Watanabe, K., Endo, K., and Kuno, K. (1996) J. Histochem. Cytochem. 44, 251-257.). The enzyme catalyzes not only the reduction of PGD(2) and PGH(2) but also that of various carbonyl compounds (Watanabe, K., Yoshida, R., Shimizu, T., and Hayaishi, O. (1985) J. Biol. Chem. 260, 7035-7041). Here, we report that retinal (vitamin A-aldehyde) was reduced to retinol (vitamin A-alcohol) dose- and time-dependently by PGF synthase using NADPH as a cofactor. The Km value of PGF synthase for retinal was about 20 microM, a same order to that for PGH(2). The conversion of retinal to retinol was also observed in cultured CIC, as demonstrated by the greenish fluorescence characteristic of retinol. Thus, retinal might be one of the natural substrates for PGF synthase in vivo, and retinol synthesized from retinal in CIC may play physiological and pathological roles in the lungs.

Animals↗
PubMed1998

Enhancement of opsin activity by all-trans-retinal.

The rod cell photoreceptor apoprotein, opsin, activates the G-protein, transducin, although at a much reduced level than light-activated rhodopsin. The ability of all-trans-retinal to enhance opsin apoprotein activity was investigated using a guanyl nucleotide exchange assay on transducin. All-trans-retinal enhanced opsin activity in a concentration-dependent manner. At high concentrations of all-trans-retinal, the activity of the all-trans-retinal-opsin complex was comparable to that from an equimolar amount of metarhodopsin(II). However, in contrast to metarhodopsin(II), the active all-trans-retinalopsin complex did not require a stable Schiff base linkage between opsin and all-trans-retinal. The lack of a stable Schiff base and differences in activity at high pH imply that opsin and all-trans-retinal form a complex that is distinct from metarhodopsin(II). The ability of all-trans-retinal to stimulate the transduction cascade may be a source of post-bleach noise in photoreceptors.

Animals↗