Retinyl ester hydrolase and the visual cycle in the chicken eye.
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.
Bustamante
J J
JJ
Division of Life Sciences, University of Texas at San Antonio 78249, USA.
Ziari
S
S
Ramirez
R D
RD
Tsin
A T
AT
D000818:Animals; D002265:Carboxylic Ester Hydrolases / Q000502:physiology*; D002645:Chickens / Q000502:physiology*; D005123:Eye / Q000201:enzymology*; D009799:Ocular Physiological Phenomena; D014785:Vision, Ocular / Q000502:physiology*
D002265:Carboxylic Ester Hydrolases; C022523:retinyl esterase