Retinyl ester hydrolase and the visual cycle in the chicken eye

1995 ◽  
Vol 269 (6) ◽  
pp. R1346-R1350
Author(s):  
J. J. Bustamante ◽  
S. Ziari ◽  
R. D. Ramirez ◽  
A. T. Tsin
Keyword(s):  
Pigment Epithelium ◽  
Retinal Pigment ◽  
Hydrolytic Activity ◽  
Retinyl Palmitate ◽  
Maximal Velocity ◽  
Visual Cycle ◽  
Retinyl Ester ◽  
Ester Hydrolase ◽  
Retinyl Ester Hydrolase ◽  
Chicken Retina

The ability of chicken retina and retinal pigment epithelium (RPE) membrane to hydrolyze vitamin A esters ([9,10(-3)H]all-trans- and 11-cis-retinyl palmitate) was studied. Hydrolytic activity within the retina was optimal at acidic pH of 5.0, whereas in the RPE significant hydrolytic activity was exhibited over a broad range of hydrogen ion concentrations. The highest rate of hydrolysis was associated with the all-trans-isomer and located within retina and RPE membranes [the apparent maximal velocity (Vmax) and Michaelis-Menten constant (Km) were 770 pmol.min.-1.mg-1 and 45 microM and 300 pmol.min-1.mg-1 and 3.6 microM, respectively[. Retinyl ester hydrolase activities for 11-cis-retinyl palmitate in the retina and RPE were correspondingly lower (apparent Vmax of 204 pmol.min.-1.mg-1 and Km of 18.5 microM in the retina; apparent Vmax of 131 pmol.min.-1.mg-1 and Km of 4 microM in the RPE). Together with results from other laboratories, results from the present study suggest that chicken retina contains important enzymes to complete the visual cycle.

Retinyl esters in the vertebrate neuroretina

1989 ◽  
Vol 256 (1) ◽  
pp. R255-R258 ◽  
Author(s):  
K. A. Rodriguez ◽  
A. T. Tsin
Keyword(s):  
Visual Pigment ◽  
High Performance ◽  
Pigment Epithelium ◽  
Retinal Pigment ◽  
Retinyl Palmitate ◽  
Visual Pigments ◽  
Pigment Synthesis ◽  
Retinyl Ester ◽  
Retinyl Ester Hydrolase ◽  
Retinyl Esters

High-performance liquid chromatography (HPLC) was employed to measure retinyl esters in the vertebrate retina. Both retina and retinal pigment epithelium (RPE) from frog, chicken, and bovine eyes were studied. In comparison to the RPE, the retina possessed a significant level of 11-cis and all trans retinyl palmitate. Using a sensitive radioassay, we also detected the presence of retinyl ester hydrolase (REH) activity in homogenates prepared from both retina and RPE. The rate of retinyl ester hydrolysis in these retinas was sufficiently high to supply retinal chromophores for the metabolic renewal and for the regeneration of visual pigments. In comparison to retinyl esters in the RPE, retinyl esters in the retina are located much closer to the sites of visual pigment synthesis and regeneration. Hence it is possible that these retinyl esters play a more important role in the visual cycle than those in the RPE.

scholarly journals Muller cells of chicken retina synthesize 11-cis-retinol

1992 ◽  
Vol 285 (3) ◽  
pp. 907-913 ◽  
Author(s):  
S R Das ◽  
N Bhardwaj ◽  
H Kjeldbye ◽  
P Gouras
Keyword(s):  
Pigment Epithelium ◽  
Retinal Pigment ◽  
Light And Electron Microscopy ◽  
Müller Cells ◽  
Neural Retina ◽  
Retinyl Palmitate ◽  
Immunocytochemical Localization ◽  
Muller Cells ◽  
Trans Isomers ◽  
Chicken Retina

The amounts of endogenous retinyl palmitate, retinol and retinaldehyde were measured in the neural retina and retinal pigment epithelium (RPE) of predominantly cone (chicken), rod (rat) and more mixed (cat, human) retinae. The ratio of 11-cis to all-trans isomers of retinyl palmitate and retinol in the neural retina and the RPE increases progressively with the increase in diurnality of the species from rat to chicken. The membrane fractions of both chicken and bovine RPE enzymically isomerize all-trans retinol to 11-cis-retinol. Chicken neural retina membranes enzymically form 11-cis-retinol and all-trans-retinyl palmitate from all-trans-retinol. Light and electron microscopy revealed no contamination of chicken neural retina by RPE. Muller cells from chicken retina were isolated, cultured and characterized by immunocytochemical localization of cellular retinaldehyde-binding protein. Cultured chicken Muller cells form all-trans-retinyl palmitate, 11-cis-retinol and 11-cis-retinyl palmitate from all-trans-retinol and release most of the 11-cis-retinol into the medium. The results indicate that chicken neural retina and Muller cells in particular synthesize 11-cis-retinoids from all-trans-retinol.

scholarly journals The hepatic retinyl ester hydrolase activity is depressed at the onset of diabetes in BB rats

2003 ◽  
Vol 89 (2) ◽  
pp. 231-238 ◽  
Author(s):  
Min Chen ◽  
Alan B. R. Thomson ◽  
Andrew T. C. Tsin ◽  
Tapan K. Basu
Keyword(s):  
Small Intestine ◽  
Vitamin A ◽  
Retinyl Palmitate ◽  
Diabetic Rats ◽  
Carrier Proteins ◽  
Retinyl Ester ◽  
Ester Hydrolase ◽  
Bb Rats ◽  
Retinyl Ester Hydrolase ◽  
Onset Of Diabetes

Dietary vitamin A as retinyl ester is hydrolysed and re-esterified with long-chain fatty acids in the small intestine. The esterified vitamin A is subsequently stored in the liver, where it is hydrolysed to free retinol to be transported by carrier proteins to the target tissue. A decreased availability of retinol carrier proteins has been suggested to be responsible for affecting metabolic availability of vitamin A in type 1 diabetes. Using BB Wistar rats, the present study was undertaken to examine whether the presence of a hyperglycaemic state modifies retinyl ester hydrolase (REH) activity in the intestine and the liver. At the onset of diabetes, hepatic REH enzymatic activity was significantly (P<0·05) decreased. However, REH activity remained unaffected in the small intestine, including both ileum and jejunum. Diabetes also resulted in decreased plasma and liver concentrations of retinol. An in vitro study was conducted to examine the effect of diabetes on the intestinal uptake of retinyl palmitate. Jejunum and ileum from diabetic and non-diabetic BB rats were incubated with labelled retinyl palmitate at different concentrations ranging from 32 to 256 nmol/l. The uptake of retinyl palmitate was increased in both diabetic and non-diabetic rats together with the increase of substrate concentration. However, no significant difference was observed in the uptake of retinyl palmitate between diabetic and non-diabetic rats. These present results suggest that the depressed hepatic REH activities may contribute to the diabetes-associated metabolic derangement of vitamin A.

Retinol dehydrogenases: Membrane-bound enzymes for the visual function

2014 ◽  
Vol 92 (6) ◽  
pp. 510-523 ◽  
Author(s):  
Mustapha Lhor ◽  
Christian Salesse
Keyword(s):  
Pigment Epithelium ◽  
Retinal Pigment ◽  
Membrane Binding ◽  
Large Family ◽  
Structural Features ◽  
Visual Cycle ◽  
Retinoid Metabolism ◽  
Current State ◽  
Membrane Bound ◽  
Membrane Bound Enzymes

Retinoid metabolism is important for many physiological functions, such as differenciation, growth, and vision. In the visual context, after the absorption of light in rod photoreceptors by the visual pigment rhodopsin, 11-cis retinal is isomerized to all-trans retinal. This retinoid subsequently undergoes a series of modifications during the visual cycle through a cascade of reactions occurring in photoreceptors and in the retinal pigment epithelium. Retinol dehydrogenases (RDHs) are enzymes responsible for crucial steps of this visual cycle. They belong to a large family of proteins designated as short-chain dehydrogenases/reductases. The structure of these RDHs has been predicted using modern bioinformatics tools, which allowed to propose models with similar structures including a common Rossman fold. These enzymes undergo oxidoreduction reactions, whose direction is dictated by the preference and concentration of their individual cofactor (NAD(H)/NADP(H)). This review presents the current state of knowledge on functional and structural features of RDHs involved in the visual cycle as well as knockout models. RDHs are described as integral or peripheral enzymes. A topology model of the membrane binding of these RDHs via their N- and (or) C-terminal domain has been proposed on the basis of their individual properties. Membrane binding is a crucial issue for these enzymes because of the high hydrophobicity of their retinoid substrates.

scholarly journals Pathophysiological features of the visual cycle, cascade and metabolic pathways in retinitis pigmentosa

2021 ◽  
Vol 14 (1) ◽  
pp. 80-88
Author(s):  
M. E. Weener ◽  
D. S. Atarshchikov ◽  
V. V. Kadyshev ◽  
I. V. Zolnikova ◽  
A. M. Demchinsky ◽  
...  
Keyword(s):  
Retinal Pigment Epithelium ◽  
Literature Review ◽  
Retinitis Pigmentosa ◽  
Metabolic Pathways ◽  
Pigment Epithelium ◽  
Retinal Pigment ◽  
Visual Signal ◽  
Visual Cycle ◽  
Target Treatment ◽  
Interphotoreceptor Matrix

This literature review offers a detailed description of the genes and proteins involved in pathophysiological processes in isolated retinitis pigmentosa (RP). To date, 84 genes and 7 candidate genes have been described for non-syndromic RP. Each of these genes encodes a protein that plays a role in vital processes in the retina and / or retinal pigment epithelium, including the cascade of phototransduction (transmission of the visual signal), the visual cycle, ciliary transport, the environment of photoreceptor cilia and the interphotoreceptor matrix. The identification and study of pathophysiological pathways affected in non-syndromic RP is important for understanding the main pathogenic ways and developing approaches to target treatment.

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