11-cis-Acyl-CoA:retinol O-acyltransferase activity in the primary culture of chicken Muller cells.
A novel retinoid cycle has recently been identified in the cone-dominated chicken retina, and this cone cycle accumulates 11-cis-retinyl esters upon light adaptation. The purpose of this study is to investigate how 11-cis-retinyl esters are formed in the retina. Primary cultures of chicken Muller cells and cell membrane were incubated with all-trans- or 11-cis-retinol to study retinyl ester synthesis. In Muller cells, esterification of 11-cis-retinol was four times greater than esterification of all-trans-retinol. In the presence of palmitoyl-CoA and CRALBP, Muller cell membranes synthesized 11-cis-retinyl ester from 11-cis-retinol at a rate which was 20-fold higher than that of all-trans-retinyl ester. In the absence of CRALBP, 11-cis-retinyl ester synthesis was greatly reduced (by 7-fold). In the absence of palmitoyl-CoA, retinyl ester synthesis was not observed. Muller cell membranes incubated with radiolabeled palmitoyl-CoA resulted in the transfer of the labeled acyl group to retinol. This acyl transfer was greatly reduced in the presence of progesterone, a known ARAT inhibitor. 11-cis-ARAT activity remained unchanged when assayed in the presence of all-trans-retinol, suggesting a distinct catalytic activity from that of all-trans-ARAT. Apparent kinetic rates for 11-cis-ARAT were 0.135 nmol min(-)(1) mg(-)(1) (V(max)) and 11.25 microM (K(M)) and for all-trans-ARAT were 0.0065 nmol min(-)(1) mg(-)(1) (V(max)) and 28.88 microM (K(M)). Our data indicate that Muller cells in the chicken retina possess 11-cis-ARAT activity, thus providing an explanation for the accumulation of 11-cis-retinyl esters in the cone cycle.
Muniz
Alberto
A
Department of Biology, University of Texas at San Antonio, San Antonio, Texas 78249, USA.
Villazana-Espinoza
Elia T
ET
Thackeray
Bridget
B
Tsin
Andrew T C
AT
D000818:Animals; D002478:Cells, Cultured; D002645:Chickens; D007536:Isomerism; D007700:Kinetics; D010171:Palmitoyl Coenzyme A / Q000378:metabolism; D011374:Progesterone / Q000494:pharmacology; D012160:Retina / Q000166:cytology / Q000201:enzymology; D051142:Retinol O-Fatty-Acyltransferase / Q000037:antagonists & inhibitors / Q000378:metabolism*
D010171:Palmitoyl Coenzyme A; D011374:Progesterone; D051142:Retinol O-Fatty-Acyltransferase