Chicken retinas contain a retinoid isomerase activity that catalyzes the direct conversion of all-trans-retinol to 11-cis-retinol

Biochemistry. 2005 Sep 6;44(35):11715-21. doi: 10.1021/bi050942m.


Vertebrate retinas contain two types of light-detecting cells. Rods subserve vision in dim light, while cones provide color vision in bright light. Both contain light-sensitive proteins called opsins. The light-absorbing chromophore in most opsins is 11-cis-retinaldehyde, which is isomerized to all-trans-retinaldehyde by absorption of a photon. Restoration of light sensitivity requires chemical re-isomerization of retinaldehyde by an enzymatic pathway called the visual cycle in the retinal pigment epithelium. The isomerase in this pathway uses all-trans-retinyl esters synthesized by lecithin retinol acyl transferase (LRAT) as the substrate. Several lines of evidence suggest that cone opsins regenerate by a different mechanism. Here we demonstrate the existence of two catalytic activities in chicken retinas. The first is an isomerase activity that effects interconversion of all-trans-retinol and 11-cis-retinol. The second is an ester synthase that effects palmitoyl coenzyme A-dependent synthesis of all-trans- and 11-cis-retinyl esters. Kinetic analysis of these two activities suggests that they act in concert to drive the formation of 11-cis-retinoids in chicken retinas. These activities may be part of a new visual cycle for the regeneration of chromophores in cones.

Publication types

  • Research Support, N.I.H., Extramural
  • Research Support, Non-U.S. Gov't
  • Research Support, U.S. Gov't, P.H.S.

MeSH terms

  • Animals
  • Cattle
  • Chickens
  • Chromatography, High Pressure Liquid
  • Esters / metabolism
  • Isomerism
  • Kinetics
  • Microsomes / enzymology
  • Models, Chemical
  • Pigment Epithelium of Eye / enzymology
  • Retina / enzymology*
  • Vitamin A / biosynthesis*
  • Vitamin A / metabolism*
  • cis-trans-Isomerases / isolation & purification*
  • cis-trans-Isomerases / metabolism*


  • Esters
  • Vitamin A
  • retinoid isomerohydrolase
  • cis-trans-Isomerases