Progress Towards Purification of the All-Trans-Retinol Isomerase, 11-Cis-Retinyl-Ester Synthase and a Novel All-Trans-Retinyl-ester Synthase in Cone-Dominant Chick Retina Membranes

Abstract

Abstract: : Purpose: A new pathway for the regeneration of visual pigment in cones has recently been reported (Mata et al. 2002). This pathway utilizes three new enzymatic activities which include an all-trans-retinol isomerase and an 11-cis-retinyl ester synthase. As a continuation of this work, progress towards the purification of these two activities as well as a novel all-trans-retinyl ester synthase will be presented. Methods: Membranes from cone-dominant, 2 week old, chick retina were prepared. These preparations were assayed in the presence of a [3H]-labeled retinoid substrate and where appropriate, [14C]-palmitoyl-coenzyme A. The catalytic activities were quantified by HPLC. Results: The all-trans-retinol isomerase and 11-cis-retinyl ester synthase found in the membrane fraction of chicken retina (Mata et al. 2002) are also present in the membrane fraction of 2-week-old chicks. In addition, a novel all-trans-retinyl ester synthase that uses palmitoyl-coenzyme A as a fatty-acyl donor has been observed in the membrane fraction of the chick retina. These activities are being fractionated by chromatographic methods. Conclusions: Current evidence suggests that the proposed pathway responsible for regeneration of visual pigments in cone-dominant retinas is present in 2-week-old chicks. A newly identified all-trans-retinyl ester synthase may play a role in this pathway. Progress towards the purification of these catalytic activities will be presented.

Keywords: retina • protein purification and characterization • enzymes/enzyme inhibitors