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1.
AUBREY KNOWLES 《Nature: New biology》1972,236(68):202-203
THE initial reaction following absorption of light in the retina is the isomerization of the 11-cis retinal chromophore of the visual pigment1. Isolated 11cis retinal will undergo the same isomerization to the all-trans form when excited by light of wavelength shorter than about 450 nm and this reaction can be sensitized to light of longer wavelengths by the addition of trace amounts of iodine to the solution2. 相似文献
2.
Sedimentation of Bovine Rhodopsin—Digitonin Micelles 总被引:1,自引:0,他引:1
RHODOPSIN, the photo-sensitive pigment of vertebrate vision receptors, consists of the lipoprotein opsin bound to the 11-cis isomer of retinal. Light isomerizes the 11-cis configuration to the all-trans, which makes the pigment unstable, leading eventually to the dissociation of the retinal from the lipoprotein. The belief that these dark steps involve conformational changes in the lipoprotein moiety stems from spectroscopic measurements which show the disappearance of lipoprotein-chromophore interactions and from kinetic and thermodynamic considerations1–5, but more direct evidence has come from the changes in circular dichroism and optical rotatory dispersion which occur with bleaching6–9. There is also an increase of Stokes radius on bleaching11. 相似文献
3.
Studies on a Missing Reaction in the Visual Cycle 总被引:1,自引:0,他引:1
DEVELOPMENT in the biochemistry of vision during the past twenty-five years can be summarized by equations (1) and (2) in Fig. 1, which envisage1 that 11-cis-retinal combines with the visual protein opsin in a dark reaction to form the photolabile complex rhodopsin, λmax 497 nm. When rhodopsin absorbs light it stimulates, through a process whose mechanism is not understood, the transmission of impulses, which are responsible for the visual sensation, although much is known about the biochemical changes accompanying the absorption of light by rhodopsin. These changes culminate in the formation of all-trans-retinal (λmax 385 nm) and opsin (equation (2), Fig. 1), through a number of intermediates2 and for the completion of the cycle one needs a molecular process which may regenerate 11-cis-retinal from all-trans-retinal (equation (3), Fig. 1). 相似文献
4.
Akiko Maeda Tadao Maeda Marcin Golczak Steven Chou Amar Desai Charles L. Hoppel Shigemi Matsuyama Krzysztof Palczewski 《The Journal of biological chemistry》2009,284(22):15173-15183
Exposure to bright light can cause visual dysfunction and retinal
photoreceptor damage in humans and experimental animals, but the mechanism(s)
remain unclear. We investigated whether the retinoid cycle (i.e. the
series of biochemical reactions required for vision through continuous
generation of 11-cis-retinal and clearance of
all-trans-retinal, respectively) might be involved. Previously, we
reported that mice lacking two enzymes responsible for clearing
all-trans-retinal, namely photoreceptor-specific ABCA4 (ATP-binding
cassette transporter 4) and RDH8 (retinol dehydrogenase 8), manifested retinal
abnormalities exacerbated by light and associated with accumulation of
diretinoid-pyridinium-ethanolamine (A2E), a condensation product of
all-trans-retinal and a surrogate marker for toxic retinoids. Now we
show that these mice develop an acute, light-induced retinopathy. However,
cross-breeding these animals with lecithin:retinol acyltransferase knock-out
mice lacking retinoids within the eye produced progeny that did not exhibit
such light-induced retinopathy until gavaged with the artificial chromophore,
9-cis-retinal. No significant ocular accumulation of A2E occurred
under these conditions. These results indicate that this acute light-induced
retinopathy requires the presence of free all-trans-retinal and not,
as generally believed, A2E or other retinoid condensation products. Evidence
is presented that the mechanism of toxicity may include plasma membrane
permeability and mitochondrial poisoning that lead to caspase activation and
mitochondria-associated cell death. These findings further understanding of
the mechanisms involved in light-induced retinal degeneration.The retinoid cycle is a fundamental metabolic process in the vertebrate
retina responsible for continuous generation of 11-cis-retinal from
its all-trans-isomer
(1-3).
Because 11-cis-retinal is the chromophore of rhodopsin and cone
visual pigments (4), disabling
mutations in genes encoding proteins of the retinoid cycle can cause a
spectrum of retinal diseases affecting sight
(3). Moreover, the efficiency
of the mammalian visual system and health of photoreceptors and retinal
pigment epithelium
(RPE)2 decrease
significantly with age. Even in the presence of a functional retinoid cycle,
A2E, retinal dimer (RALdi), and other toxic all-trans-retinal
condensation products
(5-7)
can accumulate as a consequence of aging
(8). Under experimental
conditions, these compounds can produce toxic effects on RPE cells
(9-11).
Patients affected by age-related macular degeneration, Stargardt disease, or
other retinal diseases associated with accumulation of surrogate markers, such
as A2E, all develop retinal degeneration
(12). Thus, elucidating the
fundamental causes of these age-dependent changes is of increasing importance.
Encouragingly, our understanding of both retinoid metabolism outside the eye
and production of 11-cis-retinal unique to the eye has accelerated
recently (Scheme 1)
(1-3),
and genetic mouse models are readily available to study these processes and
their potential aberrations in vivo
(13). Thus, a central question
can be addressed, namely what initiates the death of photoreceptor cells and
the underlining RPE?Open in a separate windowSCHEME 1.Retinoid flow and all-trans-retinal clearance in the visual
cycle. After diffusion from the RPE, the visual chromophore,
11-cis-retinal, combines with rhodopsin and then is photoisomerized
to all-trans-retinal. Most of the all-trans-retinal
dissociates from opsin into the cytoplasm, where it is reduced to
all-trans-retinol by RDHs, including RDH8. The fraction of
all-trans-retinal that dissociates into the disc lumen is transported
by ABCA4 into the cytoplasm
(23) before it is reduced.
All-trans-retinol then is translocated to the RPE, esterified by
LRAT, and recycled back to 11-cis-retinal. Mutations of ABCA4 are
associated with human macular degeneration, Stargardt disease, and age-related
macular degeneration (55,
56).Several mechanisms associated with retinoid metabolism may contribute to
different retinopathies (1).
For example, lack of retinoids in LRAT (lecithin:retinol acyltransferase) or
chromophore in retinoid isomerase knock-out (Rpe65-/-)
mice leads to rapid degeneration of cone photoreceptors and slowly progressive
death of rods (14). Such mice
do not produce toxic condensation products from all-trans-retinal.
Instead, their retinopathies have been attributed to continuous activation of
visual phototransduction (15)
due to either the basal activity of opsin
(16-18)
or disordered vectorial transport of cone visual pigments without bound
chromophore (19).
Paradoxically, an abnormally high flux of retinoids through the retinoid cycle
can also lead to retinopathy in other mouse models
(20,
21). Animal models featuring
anomalies in the retinoid cycle illustrate the importance of chromophore
regeneration and provide an approach to elucidating mechanisms involved in
human retinal dysfunction and disease.Recently, we showed that mice carrying a double knock-out of Rdh8
(retinol dehydrogenase 8), one of the main enzymes that reduces
all-trans-retinal in rod and cone outer segments
(22), and Abca4
(ATP-binding cassette transporter 4), which transports
all-trans-retinal from the inside to the outside of disc membranes
(23), rapidly accumulate
all-trans-retinal condensation products and exhibit accentuated
RPE/photoreceptor dystrophy at an early age
(24). Although these studies
suggest retinoid toxicity, it is still unclear if the elevated levels of
retinal and/or its condensation products, such as A2E, are the cause of this
retinopathy or merely a nonspecific reflection of impaired retinoid
metabolism. Here, we report that spent chromophore,
all-trans-retinal, is most likely responsible for photoreceptor
degeneration in Rdh8-/-Abca4-/- mice.
Toxic effects of all-trans-retinal include caspase activation and
mitochondria-associated cell death. 相似文献
5.
The mechanisms of the formation of cyclobutane dimers (CBD) of cytosine and 2,4-diaminopyrimidine were studied at the CC2 theoretical level and cc-pVDZ basis functions. Four orientations of the two monomers are explored: cys-syn, cis-anti, trans-syn, and trans-anti. The research revealed that in all cases the cyclobutane structures are formed along the 1ππ* excited-state reaction paths of the stacked aggregates. We localized the S1/S0 conical intersections mediating those transformations. The results obtained agree well with the previously reported investigations on the cis-syn cyclodimer formations of other pyrimidines. 相似文献
6.
7.
T. Reid Alderson Justin L. P. Benesch Andrew J. Baldwin 《Cell stress & chaperones》2017,22(4):639-651
In mammals, small heat-shock proteins (sHSPs) typically assemble into interconverting, polydisperse oligomers. The dynamic exchange of sHSP oligomers is regulated, at least in part, by molecular interactions between the α-crystallin domain and the C-terminal region (CTR). Here we report solution-state nuclear magnetic resonance (NMR) spectroscopy investigations of the conformation and dynamics of the disordered and flexible CTR of human HSP27, a systemically expressed sHSP. We observed multiple NMR signals for residues in the vicinity of proline 194, and we determined that, while all observed forms are highly disordered, the extra resonances arise from cis-trans peptidyl-prolyl isomerization about the G193-P194 peptide bond. The cis-P194 state is populated to near 15% at physiological temperatures, and, although both cis- and trans-P194 forms of the CTR are flexible and dynamic, both states show a residual but differing tendency to adopt β-strand conformations. In NMR spectra of an isolated CTR peptide, we observed similar evidence for isomerization involving proline 182, found within the IPI/V motif. Collectively, these data indicate a potential role for cis-trans proline isomerization in regulating the oligomerization of sHSPs. 相似文献
8.
Y Shimazaki E. Eguchi 《Journal of comparative physiology. A, Neuroethology, sensory, neural, and behavioral physiology》1995,176(5):661-671
1. | After the intact compound eyes of the butterflyPapilio xuthus were adapted to darkness, white, blue ( max 460 nm) or orange light ( max 580 nm), the eyes were separated into the distal (primary pigment cells, the dioptric apparatus and ca. 30% of retinal tissue) and the proximal layers (the rest of the retinal tissues). Each layer was separated into a supernatant and a precipitate. Both in white and blue light-adapted eyes, the amount of 11-cis 3-hydroxyretinal increased in the supernatant of the distal layer (Sup-DL) much more than it did in dark-adapted eyes. No increase was observed in the Sup-DL of orange light-adapted eyes. |
2. | When all-trans retinol (non-native chemical) was added to the Sup-DL, it was converted to all-trans retinal under the darkness, and to all-trans and 11-cis retinal by blue light irradiation. When all-trans retinal was added to the Sup-DL, the isomerization of all-trans retinal to 11-cis retinal was accelerated by the blue light. |
3. | The Sup-DL was separated into ammonium sulfate soluble (AS-sup) and insoluble (AS-ppt) fractions. The AS-ppt fraction contained 3-hydroxyretinal but no 3-hydroxyretinol. Blue light irradiation to the AS-ppt fraction induced an increase in 11-cis 3-hydroxyretinal, with a concomitant decrease in all-trans 3-hydroxyretinal. |
9.
Seung-Hye Hong Ho-Phuong-Thuy Ngo Lin-Woo Kang Deok-Kun Oh 《Biotechnology letters》2015,37(4):849-856
A recombinant alcohol dehydrogenase (ADH) from Kangiella koreensis was purified as a 40 kDa dimer with a specific activity of 21.3 nmol min?1 mg?1, a K m of 1.8 μM, and a k cat of 1.7 min?1 for all-trans-retinal using NADH as cofactor. The enzyme showed activity for all-trans-retinol using NAD + as a cofactor. The reaction conditions for all-trans-retinol production were optimal at pH 6.5 and 60 °C, 2 g enzyme l?1, and 2,200 mg all-trans-retinal l?1 in the presence of 5 % (v/v) methanol, 1 % (w/v) hydroquinone, and 10 mM NADH. Under optimized conditions, the ADH produced 600 mg all-trans-retinol l?1 after 3 h, with a conversion yield of 27.3 % (w/w) and a productivity of 200 mg l?1 h?1. This is the first report of the characterization of a bacterial ADH for all-trans-retinal and the biotechnological production of all-trans-retinol using ADH. 相似文献
10.
Takahiro Yamashita Katsuhiko Ono Hideyo Ohuchi Akane Yumoto Hitoshi Gotoh Sayuri Tomonari Kazumi Sakai Hirofumi Fujita Yasushi Imamoto Sumihare Noji Katsuki Nakamura Yoshinori Shichida 《The Journal of biological chemistry》2014,289(7):3991-4000
Opn5 is one of the recently identified opsin groups that is responsible for nonvisual photoreception in animals. We previously showed that a chicken homolog of mammalian Opn5 (Opn5m) is a Gi-coupled UV sensor having molecular properties typical of bistable pigments. Here we demonstrated that mammalian Opn5m evolved to be a more specialized photosensor by losing one of the characteristics of bistable pigments, direct binding of all-trans-retinal. We first confirmed that Opn5m proteins in zebrafish, Xenopus tropicalis, mouse, and human are also UV-sensitive pigments. Then we found that only mammalian Opn5m proteins lack the ability to directly bind all-trans-retinal. Mutational analysis showed that these characteristics were acquired by a single amino acid replacement at position 168. By comparing the expression patterns of Opn5m between mammals and chicken, we found that, like chicken Opn5m, mammalian Opn5m was localized in the ganglion cell layer and inner nuclear layer of the retina. However, the mouse and primate (common marmoset) opsins were distributed not in the posterior hypothalamus (including the region along the third ventricle) where chicken Opn5m is localized, but in the preoptic hypothalamus. Interestingly, RPE65, an essential enzyme for forming 11-cis-retinal in the visual cycle is expressed near the preoptic hypothalamus of the mouse and common marmoset brain but not near the region of the chicken brain where chicken Opn5m is expressed. Therefore, mammalian Opn5m may work exclusively as a short wavelength sensor in the brain as well as in the retina with the assistance of an 11-cis-retinal-supplying system. 相似文献
11.
Philip D. Kiser Marcin Golczak Akiko Maeda Krzysztof Palczewski 《Biochimica et Biophysica Acta (BBA)/Molecular and Cell Biology of Lipids》2012,1821(1):137-151
A major goal in vision research over the past few decades has been to understand the molecular details of retinoid processing within the retinoid (visual) cycle. This includes the consequences of side reactions that result from delayed all-trans-retinal clearance and condensation with phospholipids that characterize a variety of serious retinal diseases. Knowledge of the basic retinoid biochemistry involved in these diseases is essential for development of effective therapeutics. Photoisomerization of the 11-cis-retinal chromophore of rhodopsin triggers a complex set of metabolic transformations collectively termed phototransduction that ultimately lead to light perception. Continuity of vision depends on continuous conversion of all-trans-retinal back to the 11-cis-retinal isomer. This process takes place in a series of reactions known as the retinoid cycle, which occur in photoreceptor and RPE cells. All-trans-retinal, the initial substrate of this cycle, is a chemically reactive aldehyde that can form toxic conjugates with proteins and lipids. Therefore, much experimental effort has been devoted to elucidate molecular mechanisms of the retinoid cycle and all-trans-retinal-mediated retinal degeneration, resulting in delineation of many key steps involved in regenerating 11-cis-retinal. Three particularly important reactions are catalyzed by enzymes broadly classified as acyltransferases, short-chain dehydrogenases/reductases and carotenoid/retinoid isomerases/oxygenases. This article is part of a Special Issue entitled: Retinoid and Lipid Metabolism. 相似文献
12.
SEVERAL laboratories1–6 have recently been concerned with the mechanism of the bathochromic shift of about 120 nm which results when 11-cis retinal (λ max 380 nm) combines with the protein opsin to form rhodopsin (λmax 498 nm). A red shift of up to 186 nm is involved in the formation of iodopsin from 11-cis retinal and cone opsin7,8. The active site of bovine rhodopsin consists of the 11-cis retinylidene chromophore attached to a primary amine group of the protein forming a Schiff-base linkage of the type shown in Fig. 1, Ia. On the basis of the chemical reactions of rhodopsin and its derivatives it has been suggested that an interaction between a protonated form of the chromophore (structure of the type Ib) and a lipophilic environment contributes11 to the red shift. 相似文献
13.
J. Schwemer I. M. Pepe R. Paulsen C. Cugnoli 《Journal of comparative physiology. A, Neuroethology, sensory, neural, and behavioral physiology》1984,154(4):549-554
Summary Two retinal-binding proteins (RBP-A and RBP-B) isolated from the honeybee retina were further purified by ion-exchange chromatography. Whereas RBP-A seems to be denatured by this procedure, RBP-B remains intact with respect to its photochemical characteristics (Fig. 3a). Analysis of the geometric isomers of retinal bound to RBP-B by high performance liquid chromatography demonstrated that all-trans retinal was the chromophore of the non-irradiated RBP-B. Irradiation converted RBP-B (max 440 nm) into a photoproduct (max 370 nm) the chromophore of which was 11-cis retinal, i.e., light isomerized all-trans retinal almost exclusively to the 11-cis form (Fig. 3b). Irradiation of a solution of RBP-B in the presence of excess all-trans retinal also led to the formation of 11-cis retinal indicating that RBP catalyzes the photoisomerization of all-trans retinal. The physiological significance of RBP-B is discussed with respect to the renewal of rhodopsin.Abbreviations
RBP
retinal-binding protein
-
HPLC
high performance liquid chromatography 相似文献
14.
Maureen A. Kane Frank V. Bright Joseph L. Napoli 《Biochimica et Biophysica Acta (BBA)/General Subjects》2011
Background
Cellular retinol binding-protein I (CRBPI) and cellular retinol binding-protein II (CRBPII) serve as intracellular retinoid chaperones that bind retinol and retinal with high affinity and facilitate substrate delivery to select enzymes that catalyze retinoic acid (RA) and retinyl ester biosynthesis. Recently, 9-cis-RA has been identified in vivo in the pancreas, where it contributes to regulating glucose-stimulated insulin secretion. In vitro, 9-cis-RA activates RXR (retinoid × receptors), which serve as therapeutic targets for treating cancer and metabolic diseases. Binding affinities and structure–function relationships have been well characterized for CRBPI and CRBPII with all-trans-retinoids, but not for 9-cis-retinoids. This study extended current knowledge by establishing binding affinities for CRBPI and CRBPII with 9-cis-retinoids.Methods
We have determined apparent dissociation constants, K′d, through monitoring binding of 9-cis-retinol, 9-cis-retinal, and 9-cis-RA with CRBPI and CRBPII by fluorescence spectroscopy, and analyzing the data with non-linear regression. We compared these data to the data we obtained for all-trans- and 13-cis-retinoids under identical conditions.Results
CRBPI and CRBPII, respectively, bind 9-cis-retinol (K′d, 11 nM and 68 nM) and 9-cis-retinal (K′d, 8 nM and 5 nM) with high affinity. No significant 9-cis-RA binding was observed with CRBPI or CRBPII.Conclusions
CRBPI and CRBPII bind 9-cis-retinol and 9-cis-retinal with high affinities, albeit with affinities somewhat lower than for all-trans-retinol and all-trans-retinal.General significance
These data provide further insight into structure–binding relationships of cellular retinol binding-proteins and are consistent with a model of 9-cis-RA biosynthesis that involves chaperoned delivery of 9-cis-retinoids to enzymes that recognize retinoid binding-proteins. 相似文献15.
16.
Onder?Albayram Megan?K.?Herbert Asami?Kondo Cheng-Yu?Tsai Sean?Baxley Xiaolan?Lian Madison?Hansen Xiao?Zhen?Zhou
One of the two common hallmark lesions of Alzheimer’s disease (AD) brains is neurofibrillary tangles (NFTs), which are composed of hyperphosphorylated tau protein (p-tau). NFTs are also a defining feature of other neurodegenerative disorders and have recently been identified in the brains of patients suffering from chronic traumatic encephalopathy (CTE). However, NFTs are not normally observed in traumatic brain injury (TBI) until months or years after injury. This raises the question of whether NFTs are a cause or a consequence of long-term neurodegeneration following TBI. Two conformations of phosphorylated tau, cis p-tau and trans p-tau, which are regulated by the peptidyl-prolyl isomerase Pin1, have been previously identified. By generating a polyclonal and monoclonal antibody (Ab) pair capable of distinguishing between cis and trans isoforms of p-tau (cis p-tau and trans p-tau, respectively), cis p-tau was identified as a precursor of tau pathology and an early driver of neurodegeneration in AD, TBI and CTE. Histological studies shows the appearance of robust cis p-tau in the early stages of human mild cognitive impairment (MCI), AD and CTE brains, as well as after sport- and military-related TBI. Notably, cis p-tau appears within hours after closed head injury and long before other known pathogenic p-tau conformations including oligomers, pre-fibrillary tangles and NFTs. Importantly, cis p-tau monoclonal antibody treatment not only eliminates cis p-tau induction and tau pathology, but also restores many neuropathological and functional outcome in TBI mouse models. Thus, cis p-tau is an early driver of tau pathology in TBI and CTE and detection of cis p-tau in human bodily fluids could potentially provide new diagnostic and prognostic tools. Furthermore, humanization of the cis p-tau antibody could ultimately be developed as a new treatment for AD, TBI and CTE. 相似文献
17.
Kim Jye Lee Chang Graeme A. Dunstan Maged Peter Mansour Ian D. Jameson Peter D. Nichols 《Journal of applied phycology》2016,28(6):3363-3370
A series of novel C18–C22 trans ω3 polyunsaturated fatty acids (PUFA) with a single trans double bond in the ω3 position was found in Northern and Southern Hemisphere strains of the marine haptophyte Imantonia rotunda. The novel ω3 PUFA were identified as 18:3(9c,12c,15t) (0.2–1.8 % of total fatty acids), 18:4(6c,9c,12c,15t) (1.9–4.1 %), 18:5 (3c,6c,9c,12c,15t) (0.7–8.8 %), 20:5(5c,8c,11c,14c,17t) (1.2–4.1 %) and 22:6(4c,7c,10c,13c,16c,19t) (0.3–4.3 %), and were accompanied by larger proportions of the all cis isomers: 18:3ω3(9,12,15) (2.7–3.5 %), 18:4ω3(6,9,12,15) (9.3–14.3 %), 18:5ω3(3,6,9,12,15) (7.8–18.5 %), 20:5ω3(5,8,11,14,17) (3.2–3.9 %), 22:5ω3(7,10,13,16,19) (0.1–0.3 %) and 22:6ω3(4,7,10,13,16,19) (2.3–5.2 %). GC analysis of FAME using a non-polar column did not reveal the trans isomers as they coeluted with the all cis PUFA. However, GC using a polar column resolved the trans PUFA from the all cis PUFA, with the trans isomers eluting before the all cis isomers. GC-MS of FAME fractionated by argentation solid-phase chromatography confirmed the molecular ions of all components. FAME were derivatized to form 4,4-dimethyloxazoline (DMOX) derivatives, and GC-MS revealed the same double bond positions for each trans and cis FAME. The results suggest that the ω3 trans double bond originated from the Δ15/ω3 desaturation of 18:2(9c,12c), suggesting that this desaturase has dual cis/trans activity in these species. These results indicate that 18:3(9c,12c,15?t) was the precursor trans isomer produced for the trans series and further desaturation by the common Δ6 desaturase to produce the trans tetraene and successive elongations and desaturations led to the subsequent series of trans ω3 PUFA isomers. To our knowledge, this is the first report of these trans ω3 isomers occurring in strains of I. rotunda. These trans ω3 PUFA may be used as biomarkers in marine food webs for this species and with their unique structure may be biologically active. 相似文献
18.
A. F. Safonkin 《Entomological Review》2007,87(9):1238-1241
Changes in the number of carbon atoms and in the proportion between cis- and trans-isomers of the components of leafroller pheromones were studied. The evolution of pheromone components at the tribe level included the decrease in the number of carbon atoms and the increase in the fraction of trans-isomers. The pattern of changes in the cis- and trans-isomers ratio allows tracing the evolution of species within a single genus. 相似文献
19.
Shinya Sato Takashi Fukagawa Shuji Tachibanaki Yumiko Yamano Akimori Wada Satoru Kawamura 《The Journal of biological chemistry》2013,288(51):36589-36597
Our previous study suggested the presence of a novel cone-specific redox reaction that generates 11-cis-retinal from 11-cis-retinol in the carp retina. This reaction is unique in that 1) both 11-cis-retinol and all-trans-retinal were required to produce 11-cis-retinal; 2) together with 11-cis-retinal, all-trans-retinol was produced at a 1:1 ratio; and 3) the addition of enzyme cofactors such as NADP(H) was not necessary. This reaction is probably part of the reactions in a cone-specific retinoid cycle required for cone visual pigment regeneration with the use of 11-cis-retinol supplied from Müller cells. In this study, using purified carp cone membrane preparations, we first confirmed that the reaction is a redox-coupling reaction between retinals and retinols. We further examined the substrate specificity, reaction mechanism, and subcellular localization of this reaction. Oxidation was specific for 11-cis-retinol and 9-cis-retinol. In contrast, reduction showed low specificity: many aldehydes, including all-trans-, 9-cis-, 11-cis-, and 13-cis-retinals and even benzaldehyde, supported the reaction. On the basis of kinetic studies of this reaction (aldehyde-alcohol redox-coupling reaction), we found that formation of a ternary complex of a retinol, an aldehyde, and a postulated enzyme seemed to be necessary, which suggested the presence of both the retinol- and aldehyde-binding sites in this enzyme. A subcellular fractionation study showed that the activity is present almost exclusively in the cone inner segment. These results suggest the presence of an effective production mechanism of 11-cis-retinal in the cone inner segment to regenerate visual pigment. 相似文献
20.
N. I. Bakalenko A. V. Poznyak E. L. Novikova M. A. Kulakova 《Russian Journal of Developmental Biology》2017,48(3):211-218
Retinoic acid (RA) plays an important role in vertebrate development and regeneration. RA signalling directly regulates the expression of Hox genes, being in this way involved in the patterning of the anterior-posterior (AP) axis of vertebrate embryos. So far the relationship between retinoic acid signalling and Hox genes has been shown only for chordates. In this study we incubated juvenile worms and regenerating worms of two polychaete species from the family Nereididae, Alitta virens and Platynereis dumerilii, with all-trans-retinal, the precursor of retinoic acid. Under the influence of all-trans-retinal the anterior expression boundary of Post2 Нох gene shifted towards the anterior end both in intact and in regenerating worms of both species. Our data indicate the existence of a relationship between RA signalling and Нох genes in Protostomia. 相似文献