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PubMed1991

Geometric and energy parameters in lysine-retinal chromophores.

The parameters used in the computer program ECEPP (Empirical Conformational Energy Program for Peptides) have been expanded to cover some key elements in retinal-containing proteins. These elements are 'all-trans retinal lysine with unprotonated imine', 'all-trans retinal lysine with protonated imine', '13-cis retinal lysine with unprotonated imine' and '13-cis retinal lysine with protonated imine' respectively. The geometric parameters of these four new 'amino acid residues' were derived by optimizing their molecular structures with the AM1 Hamiltonian included in MOPAC (Molecular Orbital PACkage), and their partial atomic charges were determined with a CNDO/2 (Complete Neglect of Differential Overlap) calculation. The parameters for nonbonded interactions and torsional potentials were obtained from the existing ECEPP parameters through a logical extension. The augmented ECEPP system thus obtained can be employed to investigate the conformation of bacteriorhodopsin and its proton-pumping mechanism from an energetic point of view. The computer modeling study on bacteriorhodopsin and other seven-helix membrane proteins, e.g. serotonin receptor and dopamine receptor, is under way in the Upjohn Laboratories.

Bacteriorhodopsins↗
PubMed1996

High-performance liquid chromatography-electrospray mass spectrometry of retinoids.

High-performance liquid chromatography (HPLC)-electrospray mass spectrometry (LC-MS) was used to analyze vitamin A-active retinoids including retinoic acid, retinol, retinal, and retinyl acetate. Unlike previous LC-MS methods such as negative ion electron capture chemical ionization, no derivatization of retinoic acid was required. HPLC separations were carried out on a C30 reversed phase column with gradient elution using mobile phases containing water, methanol, and methyl-tert-butyl ether. Ammonium acetate (5 mM) was added to the mobile phase to facilitate ion pair formation during reversed phase HPLC of retinoic acid, and acetic acid (0.5% v/v) was added to the mobile phase to enhance protonation during LC-MS analysis of nonacidic retinoids. During negative ion electrospray, retinoic acid formed abundant deprotonated molecules, [M-H]-, of m/z 299 without significant fragmentation. Although retinol, retinal, and retinyl acetate did not ionize during negative ion electrospray, the positive ion electrospray mass spectra of these retinoids showed an abundant protonated molecule of m/z 285 for retinal and base peaks of m/z 269 corresponding to elimination of water or acetic acid from the protonated molecules of retinol or retinyl acetate, respectively. No ions from retinoic acid were detected during positive ion electrospray. Limits of detection for retinoic acid, retinal, retinol, and retinyl acetate were 23 pg, 1.0 ng, 0.5 ng, and 10 ng, respectively.

Diterpenes↗
PubMed1994

Enzymatic formation of 9-cis, 13-cis, and all-trans retinals from isomers of beta-carotene.

9-cis Retinoic acid is a highly preferred ligand for the nuclear retinoic acid receptor RXR. Although 9-cis retinoic acid can be formed from all-trans retinoic acid in vivo and in vitro, the nature of the isomerization process has not been defined. 9-cis-Retinoic acid might also be formed biologically from 9-cis beta-carotene, an isomer of beta-carotene commonly found in foods. We have observed that enzyme preparations of rat liver and intestine convert highly purified 9-cis beta-carotene (99.8%) to a mixture of 9-cis, all-trans, and 13-cis retinals. Highly purified all-trans beta-carotene (99.7%) and 13-cis beta-carotene (99%) are primarily converted to all-trans retinal. Several aldehyde dehydrogenases in tissues can convert retinal to retinoic acid. Although the rates of cleavage of 9-cis and 13-cis beta-carotenes are slower than that of the all-trans isomer, the oxidative conversion of 9-cis beta-carotene to 9-cis and all-trans retinals is the first identified enzymatic reaction for the formation of 9-cis retinal in animal tissues.

Aldehyde Dehydrogenase↗
PubMed2002

Beta-carotene cleavage products induce oxidative stress in vitro by impairing mitochondrial respiration.

Carotenoids are widely used as important micronutrients in food. Furthermore, carotenoid supplementation has been used in the treatment of diseases associated with oxidative stress. However, in some clinical studies harmful effects have been observed, for example, a higher incidence of lung cancer in individuals exposed to extraordinary oxidative stress. The causal mechanisms are still unclear. Carotenoid cleavage products (CCPs), including highly reactive aldehydes and epoxides, are formed during oxidative attacks in the course of antioxidative action. Here, we tested the hypothesis that CCPs may increase oxidative stress by impairing mitochondrial function. We found that CCPs strongly inhibit state 3 respiration of isolated rat liver mitochondria even at concentrations between 0.5 and 20 microM. This was true for retinal, beta-ionone, and mixtures of cleavage products, which were generated in the presence of hypochlorite to mimic their formation in inflammatory regions. The inhibition of mitochondrial respiration was accompanied by a reduction in protein sulfhydryl content, decreasing glutathione levels and redox state, and elevated accumulation of malondialdehyde. Changes in mitochondrial membrane potential favor functional deterioration of the adenine nucleotide translocator. The findings may reflect a basic mechanism of increasing the risk of cancer induced by CCPs.

Animals↗
PubMed1996

Utilizing latency for object recognition in real and artificial neural networks.

A consistent analysis of a visual scene requires the recognition of different objects. In vertebrate brains this could be achieved by synchronization of the activity of disjunct nerve cell assemblies. During such a process cross-talk between spatially adjacent image parts occurs, preventing efficient synchronization. Temporal differences, naturally introduced by stimulus latencies in every sensory system, were utilized in this study to counteract this effect and strongly improve network performance. To this end in our model the image is 'spread out' in time as a function of contrast-dependent visual latencies, and synchronization of cell assemblies occurs without mutual disturbance. The network model requires a direct link between visual latencies and the onset of synchronous oscillations in cortical cells. This was confirmed experimentally.

Cognition↗
PubMed1988

The spectral properties and photosensitivities of analogue photopigments regenerated with 10- and 14-substituted retinal analogues.

Analogues of 11-cis- and 9-cis-retinal with substitutions at positions 10 and 14 were used to regenerate analogue photopigments with two opsins: that of the transmuted (cone-like) 521-pigment of Gekko gekko and that of the rhodopsin of Porichthys notatus. The spectral absorbances and photosensitivities of the regenerated photopigments were determined and compared, first, between the two systems of analogue photopigments, and second, in the responses to the two opsins. Unlike the 10-fluoropigments, the comparable 14-compounds were significantly red-shifted by 19-30 nm and their sensitivity to light was similar to that of the parent 11-cis- and 9-cis-pigments. These were the results for both analogue pigments. In contrast, the 10-pigments were spectrally located close to the wavelengths of the parent compounds and the photosensitivity was significantly reduced, especially in the case of the 9-cis-analogues. Evidence was obtained for a steric hindrance effect at position 14, for no regeneration was obtained when methyl or ethyl groups were at this carbon. In the 10-substituted retinals, steric hindrance was noted only for the gecko; only the fluorosubstituted, but not the chloro-, the methyl- or the ethyl-substituted, retinals reacted. With the fish opsin, pigments were regenerated with all but the ethyl-substituted retinal. The gecko opsin appears to have a more restricted binding site. Another feature of the gecko was related to the chloride bathochromic and hyperchromic effects, in which the 521-pigment prepared in a chloride-deficient state has a blue-shifted spectrum compared with the spectrum obtained after the addition of chloride, and its extinction is raised by the addition of chloride to give a mean ratio of 1.23 for the two extinctions, one with, the other without, added chloride. The 11-cis-10-F-analogue pigment gave both chloride effects and the hyperchromic ratio was the same as that recorded for the native visual pigment. In contrast, the pigment formed with 11-cis-14-F-retinal gave a hyperchromic ratio significantly greater than 1.23. A similar contrast in the responses to chloride was obtained with the analogue photopigments regenerated with the 9-cis-10-F- and 9-cis-14-F-chromophores. This difference between the two systems is interpreted as the result of a specific configurational feature of the gecko opsin when in the chloride-deficient state that is relevant to the binding of the retinal analogue.(ABSTRACT TRUNCATED AT 400 WORDS)

Animals↗
PubMed1975

Inhibition of interferon action by vitamin A.

Simultaneous treatment of mouse cells with interferon and vitamin A (retinoic acid) resulted in an inhibition of interferon action. Increasing concentrations of calf serum decreased the inhibitory effect of retinoic acid on interferon action. Treatment of interferon with retinoic acid prior to the assay for interferon activity also resulted in a loss of interferon activity. Since the residual retinoic acid present after dilution of the interferon for assay was not sufficient to interfere with the assay, it is presumed that interferon and retinoic acid must interact in some fashion to inhibit interferon activity. Calf serum prevented the apparent interaction of retinoic acid and interferon. The loss of interferon activity which resulted from treatment of interferon with retinoic acid was dependent on temperature and time of incubation. Retinyl acetate (acetate ester of vitamin A) and retinal (vitamin A adehyde) only slightly inhibited interferon activity, while retinoic acid (vitamin A acid) and retinol (vitamin A alcohol) were similarly effective at inhibiting interferon activity. Another fat soluble vitamin, vitamin K1, did not inhibit interferon activity.

Animals↗
PubMed2006

S1 and S2 excited States of gas-phase Schiff-base retinal chromophores.

Photoabsorption studies of 11-cis and all-trans Schiff-base retinal chromophore cations in the gas phase have been performed at the electrostatic ion storage ring in Aarhus. A broad absorption band due to the optically allowed excitation to the first electronically excited singlet state (S1) is observed at around 600 nm. A second "dark" excited state (S2) just below 400 nm is reported for the first time. It is located approximately 1.2 eV above S1 for both chromophores. The S2 state was not visible in a solution measurement where only one highly blueshifted absorption band corresponding to the first excited state was visible. Knowledge of the position of the excited states in retinal is essential for the understanding of the fast photoisomerization in, for example, visual pigments.

Gases↗
PubMed2004

The quantum topological electrostatic potential as a probe for functional group transferability.

The electrostatic potential can be used as an appropriate and convenient indicator of how transferable an atom or functional group is between two molecules. Quantum-chemical topology (QCT) is used to define the electron density of a molecular fragment and the electrostatic potential it generates. The potential generated on a grid by the terminal aldehyde group of the biomolecule retinal is compared with the corresponding aldehyde group in smaller molecules derived from retinal. The terminal amino group in the free amino acid lysine was treated in a similar fashion. Each molecule is geometry-optimized by an ab initio calculation at B3LYP/6-311G+(2d,p)//HF/6-31G(d) level. The amino group in lysine is very little influenced by any part of the molecule further than two C atoms away. However, the aldehyde group in retinal is influenced by molecular fragments six C atoms away. This dramatic disparity is ascribed to the difference in saturation in the carbon chains; retinal contains a conjugated hydrocarbon chain but lysine an aliphatic one.

Aldehydes↗
PubMed1992

A multimicroelectrode system composed of independent glass micropipettes with an eccentric tip structure for simultaneous intracellular recording.

A glass multimicroelectrode system for simultaneous intracellular recordings is described in which four pieces of micropipettes with rectangular cross section are arranged in a square compartment. Each tip position is shifted from the central axis of the electrode stem toward the crest line of its corner. Such micropipettes are mechanically bundled to one another so that the horizontal spacing among tips can be made shorter than the electrode diameter and components are independently penetrable. This paper offers techniques for fabricating such an eccentric micropipette. Finally, an example of simultaneous recordings of intracellular membrane potentials in the carp retina is demonstrated. This paper provides a technique which would allow researchers to record from three or four neurons simultaneously.

Animals↗
PubMed2006

Bacteriorhodopsin chimeras containing the third cytoplasmic loop of bovine rhodopsin activate transducin for GTP/GDP exchange.

The mechanisms by which G-protein-coupled receptors (GPCRs) activate G-proteins are not well understood due to the lack of atomic structures of GPCRs in an active form or in GPCR/G-protein complexes. For study of GPCR/G-protein interactions, we have generated a series of chimeras by replacing the third cytoplasmic loop of a scaffold protein bacteriorhodopsin (bR) with various lengths of cytoplasmic loop 3 of bovine rhodopsin (Rh), and one such chimera containing loop 3 of the human beta2-adrenergic receptor. The chimeras expressed in the archaeon Halobacterium salinarum formed purple membrane lattices thus facilitating robust protein purification. Retinal was correctly incorporated into the chimeras, as determined by spectrophotometry. A 2D crystal (lattice) was evidenced by circular dichroism analysis, and proper organization of homotrimers formed by the bR/Rh loop 3 chimera Rh3C was clearly illustrated by atomic force microscopy. Most interestingly, Rh3C (and Rh3G to a lesser extent) was functional in activation of GTPgamma35S/GDP exchange of the transducin alpha subunit (Galphat) at a level 3.5-fold higher than the basal exchange. This activation was inhibited by GDP and by a high-affinity peptide analog of the Galphat C terminus, indicating specificity in the exchange reaction. Furthermore, a specific physical interaction between the chimera Rh3C loop 3 and the Galphat C terminus was demonstrated by cocentrifugation of transducin with Rh3C. This Galphat-activating bR/Rh chimera is highly likely to be a useful tool for studying GPCR/G-protein interactions.

Animals↗
PubMed1996

Retinoid induction of CRABP II mRNA in human dermal fibroblasts: use as a retinoid bioassay.

Cellular retinoic acid binding protein II (CRABP II) mRNA is selectively induced by all-trans retinoic acid in human skin and dermal fibroblasts. In order to determine whether this response can be used as a reliable measure of retinoid potency and activity, we treated human skin fibroblasts for 24 h with increasing concentrations of several natural and synthetic retinoids. CRABP II mRNA levels were measured by quantitative Northern blotting and compared, when possible, with those obtained after topical application of the same retinoids to human skin. All eight active retinoids tested induced a concentration-dependent CRABP II mRNA response in the fibroblast assay. In contrast, one known inactive retinoid (meta-carboxy TTNPB), differing from the active form only in the position of the carboxyl substituent, failed to evoke a response. The fibroblast and human skin bioassays agreed with respect to relative potency and response amplitude for three of the three retinoids tested. Retinoic acid was approximately 10-fold more potent than retinal in both assays, suggesting that oxidation to retinoic acid underlies the activity of retinol in fibroblasts as well as in intact skin. In support of this hypothesis, treatment with liarozole, an inhibitor of P450-mediated retinoic acid oxidative catabolism, significantly increased fibroblast CRABP II mRNA levels and potentiated the effects of retinol by 1.5-fold at concentrations at which it had no effect on its own. Taken together, these results identify the fibroblast CRABP II response as a reproducible measure of retinoid bioactivity with promise as a predictor of human skin responses and further suggest that metabolism is an important determinant of retinoid bioactivity in vivo.

Biological Assay↗
PubMed1990

Metabolism of natural retinoids in psoriatic epidermis.

Synthetic retinoids that have distinct therapeutic activity on psoriatic plaques act at least in part through the metabolic pathways of natural retinoids. The metabolism of retinol, retinal, and retinoic acid in human epidermis in general and psoriatic plaques in particular has not been previously analyzed. This appears to be an important issue, because enzymatic formation of retinoic acid from retinol within target cells is thought to be the source of biologically active retinoic acid therein and might be subjected to regulation. We found chat the enzymatic system that transforms (3H)retinol into (3H)retinoic acid is detectable in psoriatic plaques (0.33 +/- 0.07 pmol/h/mg protein) but only in trace amounts in normal epidermis. The activity due to alcohol deshydrogenase seems not to be involved in this process. (3H)retinal was found to be either reduced into retinol or oxidized into retinoic acid, depending on the ratio of NAD to NADH (the oxidized arid reduced nicotinamide-adenine dinucleotide, respectively); the former reaction was higher in psoriatic plaques than in normal epidermis.

Humans↗
PubMed1991

Increased removal of remnants of triglyceride-rich lipoproteins on a diet rich in polyunsaturated fatty acids.

We studied the effect of two diets, one rich in polyunsaturated and the other in saturated fatty acids, on the postprandial processing of exogenous and endogenous triglyceride-rich lipoproteins (chylomicrons, very-low-density lipoproteins, and their remnants). For this purpose, 12 normolipidaemic young volunteers were fed, in a cross-over design of 9 days on each diet, either a diet rich in saturated fat (21% of their daily energy intake from saturated fat, 12% from monounsaturated fat, and 3% from polyunsaturated fat) or a diet rich in polyunsaturated fat (10% saturated fat, 9% monounsaturated fat, and 18% polyunsaturated fat) (P/S ratios 0.14 and 1.8, respectively). On the last day of each dietary period blood samples were drawn six times over a 24-h period for determination, by densitometric scanning of SDS gels, of the diurnal pattern of apoprotein B-48 and B-100 in the d less than 1.019 g ml-1 fractions, as estimates for the processing of chylomicrons and very-low-density lipoproteins. In addition to the usual decrease in the fasting and diurnal concentrations of total serum cholesterol and of cholesterol in the low-density lipoprotein fractions (between 15 and 21%), the diet rich in polyunsaturated fat resulted in 43% lower daily concentrations of chylomicrons and their remnants. This was due to differences in the clearance rate of chylomicrons and their remnants, rather than to differences in the absorption rate of exogenous fat. In addition, the concentrations of very low density lipoproteins and their remnants during the day were 20% lower on the diet rich in polyunsaturated fat.(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗
PubMed2005

Retinal biosynthesis in Eubacteria: in vitro characterization of a novel carotenoid oxygenase from Synechocystis sp. PCC 6803.

Retinal and its derivatives represent essential compounds in many biological systems. In animals, they are synthesized through a symmetrical cleavage of beta-carotene catalysed by a monooxygenase. Here, we demonstrate that the open reading frame sll1541 from the cyanobacterium Synechocystis sp. PCC 6803 encodes the first eubacterial, retinal synthesizing enzyme (Diox1) thus far reported. In contrast to enzymes from animals, Diox1 converts beta-apo-carotenals instead of beta-carotene into retinal in vitro. The identity of the enzymatic product was proven by HPLC, GC-MS and in a biological test. Investigations, of the stereospecifity showed that Diox1 cleaved only the all-trans form of beta-apo-8'-carotenal, yielding all-trans-retinal. However, Diox1 exhibited wide substrate specificity with respect to chain-lengths and functional end-groups. Although with divergent Km and Vmax values, the enzyme converted beta-apo-carotenals, (3R)-3-OH-beta-apo-carotenals as well as apo-lycopenals into retinal, (3R)-3-hydroxy-retinal and acycloretinal respectively. In addition, the alcohols of these substrates were cleaved to yield the corresponding retinal derivatives.

Animal Feed↗