AJP - Regulatory, Integrative and Comparative Physiology, Vol 269, Issue 6 1346-R1350, Copyright © 1995 by American Physiological Society
Retinyl ester hydrolase and the visual cycle in the chicken eye
J. J. Bustamante, S. Ziari, R. D. Ramirez and A. T. Tsin
Division of Life Sciences, University of Texas at San Antonio 78249, USA.
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.
