Photochemistry and dark equilibrium of retinal isomers and bacteriorhodopsin isomers.
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Bacteriorhodopsins↗
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Visual chromophore electronic structure.
The implications that recent work on the electronic structure of polyenes have for the low lying electronic states of retinal reviewed and a very simple model for the diffusenesss of the absorption spectra of visual chromophores is presented.
Chemical Phenomena↗
Spectral studies on the conformation of rhodopsin.
A summary is given of visible and ultraviolet spectral studies which deal with the conformation of rhodopsin in situ and solubilized with detergent. Emphasis is placed on studies which give specific information about the macromolecular structure and which set quantitative limits on the magnitude of light-induced conformational changes.
Animals↗
Retinal damage by light: possible implication of singlet oxygen.
A new hypothesis is proposed in an attempt to explain the mechanism of the irreversible damage which can be induced in the retina by visible light. Upon illumination, retinal generates singlet oxygen and this reactive species can produce lipid peroxidation which in turn may induce membrane instability.
Light↗
Spectral transitions in purple membranes from Halobacterium halobium. I. Effect of preliminary illumination on photochemical processes.
The effect of preliminary illumination of purple membranes by yellow light on the difference spectra of short-lived intermediates has been studied. It has been found that changes of the optical density of two of these intermediates, which have the maxima of the difference spectrum at 412 nm and 650 nm, coincides well with the kinetics off the known reversible transitions of the main band of the purple membrane absorption (560 570), i.e., 13-cis-trans transitions. The changes at 412 nm and 650 nm are proportional to the concentration changes of the all-trans retinal and 13-cis retinal, respectively. It was concluded that the formation of the short-lived 412 and 650 intermediates occurs in different photochemical cycles. The pH is found to affect the formation of the 650 intermediate.
Bacteriorhodopsins↗
The rhodopsins: structure and function. Introduction.
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GTP-Binding Proteins↗
Development of neuronal connections in chick embryonic retino-tectal system: an overview.
Synaptogenesis has been examined in the retino-tectal system of the chick embryo both biochemically and morphologically. We have evaluated the amount and the rate transport of glycoproteins synthetized in retinal ganglion cells and axonally transported to retinal nerve endings. The distribution of glycoproteins inside the tectum shows that they are part of the synaptosomal membrane either because they are incorporated in it "en route" or because they flow through an axolemmal flow. The role they might play in the building up of the synaptic membrane is discussed in relation to the maturation of synaptic contacts, observed either with E-PTA staining method or with routine fixation methods. The distribution of a carbohydrate binding protein was followed with histochemical techniques. This protein is synthesized by the matching tectal neurons, and its synthesis is developmentally regulated. It distribution is affected by innervation. All of these findings are discussed in relation to the hypothesis that three different steps are involved in embryonic synaptogenesis. These three steps are: 1) interneuronal recognition; 2) formation of initial contact, and 3) formation of synapses. The possibility that different kinds of cell surface macromolecules might play a different role is also discussed.
Animals↗
The relationship between the chromophore moiety and the cation binding sites in bacteriorhodopsin.
Bleaching of the purple membrane strongly reduces the number of divalent cation binding sites as well as their affinities. Conversely, deionization of the bleached membrane drastically inhibits the chromophore regeneration. Proteolysis experiments using bromelain show that the bleached membrane has an additional cleavage site probably located at the fifth loop, whereas in the blue membrane, the C-terminal tail is no longer susceptible to proteolysis. It is suggested that there exists a close relationship between the retinal environment and one or more of the cation binding sites.
Bacteriorhodopsins↗
Survival of cone responses in postmortem human retina.
A cone-mediated electroretinogram was recordable from human retinas 17-18 hours postmortem, after regeneration of visual pigments by application of 11-cis and 9-cis retinal. The cone was separated from the rod component by stimulation with flickering red light. In addition to these neuronal responses, a P2 and a slow P3 were present.
Adolescent↗
Determination of retinal chromophore structure in bacteriorhodopsin with resonance Raman spectroscopy.
The analysis of the vibrational spectrum of the retinal chromophore in bacteriorhodopsin with isotopic derivatives provides a powerful "structural dictionary" for the translation of vibrational frequencies and intensities into structural information. Of importance for the proton-pumping mechanism is the unambiguous determination of the configuration about the C13=C14 and C=N bonds, and the protonation state of the Schiff base nitrogen. Vibrational studies have shown that in light-adapted BR568 the Schiff base nitrogen is protonated and both the C13=C14 and C=N bonds are in a trans geometry. The formation of K625 involves the photochemical isomerization about only the C13=C14 bond which displaces the Schiff base proton into a different protein environment. Subsequent Schiff base deprotonation produces the M412 intermediate. Thermal reisomerization of the C13=C14 bond and reprotonation of the Schiff base occur in the M412------O640 transition, resetting the proton-pumping mechanism. The vibrational spectra can also be used to examine the conformation about the C--C single bonds. The frequency of the C14--C15 stretching vibration in BR568, K625, L550 and O640 argues that the C14--C15 conformation in these intermediates is s-trans. Conformational distortions of the chromophore have been identified in K625 and O640 through the observation of intense hydrogen out-of-plane wagging vibrations in the Raman spectra (see Fig. 2). These two intermediates are the direct products of chromophore isomerization. Thus it appears that following isomerization in a tight protein binding pocket, the chromophore cannot easily relax to a planar geometry. The analogous observation of intense hydrogen out-of-plane modes in the primary photoproduct in vision (Eyring et al., 1982) suggests that this may be a general phenomenon in protein-bound isomerizations. Future resonance Raman studies should provide even more details on how bacterio-opsin and retinal act in concert to produce an efficient light-energy convertor. Important unresolved questions involve the mechanism by which the protein catalyzes deprotonation of the L550 intermediate and the mechanism of the thermal conversion of M412 back to BR568. Also, it has been shown that under conditions of high ionic strength and/or low light intensity two protons are pumped per photocycle (Kuschmitz & Hess, 1981). How might this be accomplished?(ABSTRACT TRUNCATED AT 400 WORDS)
Bacteriorhodopsins↗
Hydrophobic organization of alpha-helix membrane bundle in bacteriorhodopsin.
The hydrophobic organization of the intramembrane alpha-helical bundle in bacteriorhodopsin (BRh) was assessed based on a new approach to characterization of spatial hydrophobic properties of transmembrane (TM) alpha-helical peptides. The method employs two independent techniques: Monte Carlo simulations of nonpolar solvent around TM peptides and analysis of molecular hydrophobicity potential on their surfaces. The results obtained by the two methods agree with each other and permit precise hydrophobicity mapping of TM peptides. Superimposition of such data on the experimentally derived spatial model of the membrane moiety together with 2D maps of hydrophobic hydrophilic contacts provide considerable insight into the hydrophobic organization of BRh. The helix bundle is stabilized to a large extent by hydrophobic interactions between helices--neighbors in the sequence of BRh, by long-range interactions in helix pairs C-E, C-F, and C-G, and by nonpolar contracts between retinal and helices C, D, E, F. Unlike globular proteins, no polar contacts between residues distantly separated in the sequence of BRh were found in the bundle. One of the most striking results of this study is the finding that the hydrophobic organization of BRh is significantly different from those in bacterial photoreaction centers. Thus, TM alpha-helices in BRh expose their most nonpolar sides to the bilayer as well as to the neighboring helices and to the interior of the bundle. Some of them contact lipids with their relatively hydrophilic surfaces. No correlation was found between disposition of the most hydrophobic and the most variable sides of the TM helices.
Bacteriorhodopsins↗
Retinoids, a new class of compounds with prophylactic and therapeutic activities in oncology and dermatology.
A review of recent investigations in the retinoid field is presented. Retinoic acid exerts a prophylactic and a therapeutic effect on chemically induced benign and malignant epithelial tumors in mice. In clinical studies positive therapeutic results have been obtained in patients with preneoplastic and neoplastic epithelial lesions. However, treatment with retinoic acid is limited by serious side effects (hypervitaminosis A syndrome). Therefore, the synthesis of analogs of retinoic acid (retinoids) possessing a more favorable therapeutic ratio has been initiated. Among a large series of synthesized compounds, certain aromatic analogs proved to have a particularly favorable therapeutic ratio. The structure-activity relationship of the most active retinoids is discussed including some biological data concerning prophylaxis and therapy of epithelial tumors. The total synthesis of retinoids according to various building schemes is discussed in detail. Methods for the synthesis of the cyclic end group, of the polyene chain component, and of the full retinoid skeleton are described. Metabolic studies of retinoic acid and of the most active retinoid, as well as the synthesis of some isolated metabolites are outlined. Suggestions concerning the mechanism of action of retinoids are made. Some clinical results on the treatment of acne, psoriasis and precancerous conditions are reported.
Animals↗
Comparative studies on the fine structure of purple membrane from Halobacterium Cutirubrum and Halobacterium Halobium.
Direct comparison of the absorption and circular dichroic spectra of dark- and light-adapted purple membrane from Halobacterium cutirubrum and Halobacterium halobium indicated no apparent species differences. In addition, sequential bleaching and regeneration of the purple membrane with concomitant monitoring of the absorption and circular dichroic spectra showed no species differences as well. Furthermore, perturbation of the structure of the purple membrane from either species with a detergent, Triton X-100, yielded similar spectral changes. It was concluded: (i) no apparent differences exist in the molecular organization and protein fine structure of the two purple membranes, (ii) if exciton interaction among the retinal chromophores is a reasonable possibility in the case of the purple membrane from Halobacterium halobium, it must be similarly so for the membrane from Halobacterium cutirubrum, (iii) the effects of light adaptation on the membrane structure of both species are essentially the same, and (iv) the underlying molecular mechanisms for the bleaching and regenerative processes must be similar, if not identical, for the purple membranes of the two species.
Bacteriorhodopsins↗
Intrinsic control of rhabdom size and rhodopsin content in the crab compound eye by a circadian biological clock.
Under conditions of constant darkness, rhabdom volume and the amount of visual pigment chromophore show circadian changes in the compound eye of the crab Hemigrapsus sanguineus. The present results indicate that an intrinsic circadian biological clock is involved in the control of the changes.
Animals↗
Inhibition of human non-pancreatic phospholipases A2 by retinoids and flavonoids. Mechanism of action.
The interaction of retinoids and flavonoids with phospholipases A2 (PLA2) was studied to assess the mechanism of inhibition. Retinoids, such as retinal, retinol, retinoic acid and retinol acetate, and flavonoids, such as quercetin, rutin, morin and sciadopitysin, inhibit Ca2+-dependent PLA2 activity of human synovial fluid (HSF) in vitro in a dose-dependent fashion; ID20S ranged from 2-8 microM. Retinal inhibited neutral active Ca2+-dependent PLA2S from human platelets, human plasma, human polymorphonuclear leukocytes and Naja mossambica mossambica venom in a dose-dependent manner while quercetin inhibits extracellular PLA2 activities of human plasma, HSF and N. m. mossambica venom in a dose-dependent manner but not PLA2 activity derived from human platelets and polymorphomonuclear leukocytes. Inhibition of PLA2 activity by both flavonoid and retinoids were independent of Ca2+ or Na+. Increasing substrate concentration (9-144 nmols) relieved the inhibition of HSF-PLA2 activity by quercetin indicating probable interaction with the substrate. The inhibition by retinal is independent of substrate concentration suggesting that inhibition by retinal is probably due to direct interaction with the enzyme. both retinal and quercetin quenched the relative fluorescent intensity of N. m. mossambica PLA2 and in a dose-dependent manner in the same concentration range at which they inhibit in vitro PLA2 activity. Retinal and quercetin shift the thermotropic phase transition of distearoylphosphatidylethanolamine (DSPE) liposomes. Both compounds broadened the transition peak, shifted the Tm to lower temperature, and decreased enthalpy significantly. These findings indicate that inhibition of non-pancreatic human PLA2S by retinoids and flavonoids can be mediated by interaction with enzyme and/or substrate.
Arthritis↗
Retinol: predominant form of vitamin A in corpus luteum.
We could not confirm the results of a previous research group which stated that retinal (vitamin A aldehyde) is present in corpus luteum of bovine origin. On the contrary we establish the occurrence of retinol (vitamin A alcohol) in both human and bovine corpora lutea. Identity of the compound is confirmed by its chromatographic behavior on high performance liquid chromatographic systems (adsorption and reversed phase) and by spectrometric analysis (UV, fluorimetry).
Animals↗
Phyletic aspects of the distribution of 3-hydroxyretinal in the class Insecta.
The distribution of 3-hydroxyretinal (R3), a recently discovered retinoid used as the visual pigment chromophore in some insects, was investigated in the class Insecta using HPLC technology. We studied 138 species in 24 orders, sampling from a wide range of taxonomic groups as well as varied habitats. In addition to groups already known to have R3, we find this retinoid in Hemiptera (suborder Heteroptera), Plecoptera, Megaloptera, and Hymenoptera. We also find retinal (R1) in Hemiptera (suborder Homoptera), Mecoptera, and Trichoptera, groups previously thought to have only R3. The pattern of R3 occurrence indicates that this retinoid cannot be considered a phylogenetic marker, having a scattered distribution in the class Insecta as well as within some orders of insects. Several environmental factors that might influence the selection of chromophore have been considered, but none correlates with its distribution. The evolutionary reasons for the pattern of occurrence of R3 therefore remain unknown.
Animals↗
Prediction of light-induced transient thermal response of the retina.
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Body Temperature Regulation↗