May 2003
Volume 44, Issue 13
Free
ARVO Annual Meeting Abstract  |   May 2003
The Effect of the Chromophore Switch From A1 to A2 on Spectral and Thermal Properties of the Rod Visual Pigment in the Bullfrog, Rana catesbeiana
Author Affiliations & Notes
  • P. Ala-Laurila
    Lab. of Biomedical Engineering, Helsinki University of Technology, Espoo, Finland
  • R. Albert
    Lab. of Biomedical Engineering, Helsinki University of Technology, Espoo, Finland
  • P. Saarinen
    Dept. of Biosciences, University of Helsinki, Helsinki, Finland
  • A. Koskelainen
    Dept. of Biosciences, University of Helsinki, Helsinki, Finland
  • K. Donner
    Dept. of Biosciences, University of Helsinki, Helsinki, Finland
  • Footnotes
    Commercial Relationships  P. Ala-Laurila, None; R. Albert, None; P. Saarinen, None; A. Koskelainen, None; K. Donner, None.
  • Footnotes
    Support  Supported by the Academy of Finland (grants 49947, 51681 and 36154)
Investigative Ophthalmology & Visual Science May 2003, Vol.44, 2004. doi:
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      P. Ala-Laurila, R. Albert, P. Saarinen, A. Koskelainen, K. Donner; The Effect of the Chromophore Switch From A1 to A2 on Spectral and Thermal Properties of the Rod Visual Pigment in the Bullfrog, Rana catesbeiana . Invest. Ophthalmol. Vis. Sci. 2003;44(13):2004.

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

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Abstract

Abstract: : Purpose: To measure the change in the energy needed for photoactivation (Ea) of the rod visual pigment when the chromophore is switched from retinal (A1) to 3-dehydroretinal (A2) in rods of the adult bullfrog, Rana catesbeiana. This well-characterized model species1,2 offers a rhodopsin-porphyropsin pair for which the rates of thermal ("dark") isomerizations3 as well as the cDNA sequence of the opsin4 are available for functional comparisons. Methods: Absorbance spectra of rhodopsin and porphyropsin rods were recorded by single-cell microspectrophotometry (MSP) and spectral sensitivities were determined by electroretinogram (ERG) recording across the ventral (rhodopsin) and dorsal (porphyropsin) fields of the isolated retina at two temperatures, 8.5 oC and 28.5 oC. The photoactivation energies (Ea) of the two pigments were estimated based on the temperature effect on relative spectral sensitivities at long wavelengths.5, 6 Results: Our Ea-estimates (mean ± SEM) for rhodopsin and porphyropsin rods are 46.5 ± 0.8 kcal/mol and 44.2 ± 0.9 kcal/mol respectively. Thus the chromophore switch from A1 to A2 was associated with a statistically significant (P < 0.09) decrease of Ea. The absorbance maxima of the two pigments were at 501 nm and 525 nm, respectively. Conclusions: The lowering of the photoactivation energy due to the switch from A1 to A2 correlates both with the previously observed increase in thermal isomerization rate3 and the red-shift of the spectrum, as originally hypothesized by Horace Barlow.7 1Reuter et al., J. Gen. Physiol. 58, 351-371 (1971). 2Fong et al., Vision Res. 25, 1387-1397 (1985). 3Donner et al., J. Physiol. 428, 673-692 (1990). 4Kayada et al., Comp. Biochem. Physiol. 110B, 599-604 (1995). 5Koskelainen et al., Nature 403, 220–223 (2000). 6Ala-Laurila et al., Visual Neurosci. (in press). 7Barlow, Nature 179, 255-256 (1957).

Keywords: photoreceptors • electroretinography: non-clinical • protein structure/function 
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