March 2012
Volume 53, Issue 14
ARVO Annual Meeting Abstract  |   March 2012
Thermal isomerization of cone pigments
Author Affiliations & Notes
  • Masahiro Kono
    Ophthalmology, Medical Univ of South Carolina, Charleston, South Carolina
  • Patrice W. Goletz
    Ophthalmology, Medical Univ of South Carolina, Charleston, South Carolina
  • Footnotes
    Commercial Relationships  Masahiro Kono, None; Patrice W. Goletz, None
  • Footnotes
    Support  NIH grant EY019515; Research to Prevent Blindness
Investigative Ophthalmology & Visual Science March 2012, Vol.53, 3361. doi:
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      Masahiro Kono, Patrice W. Goletz; Thermal isomerization of cone pigments. Invest. Ophthalmol. Vis. Sci. 2012;53(14):3361.

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      © ARVO (1962-2015); The Authors (2016-present)

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Purpose: : Cone visual pigments are notoriously known to be unstable in the dark. This has been attributed to thermal isomerization of the chromophore based primarily on downstream signaling data. The purpose of this study is to determine thermal isomerization of human cone visual pigments directly.

Methods: : Cone opsins were transiently expressed in COS-1 cells, and pigments were generated with 11-cis retinal. They were then immunopurified in 0.1% dodecylmaltoside. Thermal isomerization was measured spectrophotometrically by monitoring the change in absorbance at 380 nm in the presence of 10-fold excess of 11-cis retinal at different temperatures. Isomeric content was confirmed by HPLC.

Results: : Chromatograms indicated that 11-cis retinal does thermally isomerize to all-trans retinal in the presence of cone opsin faster than retinal alone. With a 10-fold excess of 11-cis retinal present, multiple turnovers could be assessed by following changes in absorbance at 380nm because of differences in extinction coefficients between the 11-cis and all-trans retinals. As temperature is increased, isomerization rates accelerated; however, the protein denatured with time as judged by loss of pigment. From initial rates of isomerization at different temperatures, we could estimate activation energy of isomerization to be about 20-25 kcal/mol.

Conclusions: : Cone opsins do accelerate thermal isomerization of 11-cis retinal.

Keywords: color pigments and opsins • retinoids/retinoid binding proteins 

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