scholarly journals Substrate specificity of retinyl ester hydrolase activity in retinal pigment epithelium

1998 ◽  
Vol 39 (3) ◽  
pp. 604-612 ◽  
Author(s):  
Jennifer R. Mata ◽  
Nathan L. Mata ◽  
Andrew T.C. Tsin
Keyword(s):  
Retinal Pigment Epithelium ◽  
Substrate Specificity ◽  
Pigment Epithelium ◽  
Retinal Pigment ◽  
Hydrolase Activity ◽  
Retinyl Ester ◽  
Ester Hydrolase ◽  
Retinyl Ester Hydrolase

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.

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