The relation between spectral and thermal properties of vertebrate visual pigments

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dc.contributor Aalto-yliopisto fi
dc.contributor Aalto University en
dc.contributor.author Ala-Laurila, Petri
dc.date.accessioned 2012-02-10T09:09:54Z
dc.date.available 2012-02-10T09:09:54Z
dc.date.issued 2003-12-13
dc.identifier.isbn 951-22-6831-0
dc.identifier.uri https://aaltodoc.aalto.fi/handle/123456789/2146
dc.description.abstract This thesis investigates the relation between three important functional properties of visual pigments: 1) the absorbance spectrum, 2) the energy needed for activation and 3) the thermal stability. The study is based on measurement of spectral absorbance and spectral sensitivity in 10 visual pigments in rod and cone photoreceptor cells from the retinas of 6 vertebrate species and on data from the literature. Absorbance spectra were recorded by single-cell mictrospectrophotometry (MSP) and spectral sensitivities by electroretinogram recording (ERG) across the isolated retina. For each pigment, measurements were conducted at two or more temperatures in the range 0-40 °C. The photoactivation energies of the visual pigments were determined from the temperature-dependence of spectral sensitivity in the long-wavelength range. Thermal activation rates of rod and cone pigments were collected from the literature. One objective was to test the hypothesis that there is a strict coupling between the energy needed for photoactivation (Ea) and the wavelength of maximum absorbance (λmax) of visual pigments. The greater goal was to clarify the relation between the energies required for thermal and photic activation and thus explain the experimentally observed correlation between λmax and the rate of spontaneous, thermal activation of pigments. The measurements showed that there is no necessary physical coupling between Ea and λmax. A strict inverse proportionality (Ea ∝ 1/λmax) holds only in the simple case where spectral tuning is achieved by a change of chromophore, with no change in the protein (opsin) part of the pigment. On the other hand, a significant correlation between Ea and 1/λmax was found in the full set of 12 visual pigments considered (including two invertebrate pigments). A new model for thermal activation is proposed, with a consequent dependence of the activation rate on λmax. The crucial point is that the statistics of thermal activation is determined by the presence of internal energy in a large number of vibrational modes of the visual pigment molecule. The great discrepancy between photoactivation energies and thermal activation energies as estimated in earlier work then disappears as an analytical artifact. The main conclusion is that thermal and photic activation of visual pigments may follow the same molecular route from a very early stage (isomerization of the chromophore in the native conformation of rhodopsin). Furthermore, the model accurately predicts the correlation between the wavelength of maximum absorbance and the rate of thermal activation observed in the whole set of visual pigments studied. en
dc.format.extent 103, [58]
dc.format.mimetype application/pdf
dc.language.iso en en
dc.publisher Helsinki University of Technology en
dc.publisher Teknillinen korkeakoulu fi
dc.relation.haspart Koskelainen A., Ala-Laurila P., Fyhrquist N. and Donner K., 2000. Measurement of thermal contribution to photoreceptor sensitivity. Nature 403, No. 6766, pages 220-223. [article1.pdf] © 2000 Nature Publishing Group. By permission.
dc.relation.haspart Ala-Laurila P., Saarinen P., Albert R., Koskelainen A. and Donner K., 2002. Temperature effects on spectral properties of red and green rods in toad retina. Visual Neuroscience 19, No. 6, pages 781-792.
dc.relation.haspart Ala-Laurila P., Albert R.-J., Saarinen P., Koskelainen A. and Donner K., 2003. The thermal contribution to photoactivation in A2 visual pigments studied by temperature effects on spectral properties. Visual Neuroscience 20, No. 4, pages 411-419.
dc.relation.haspart Ala-Laurila P., Pahlberg J., Koskelainen A. and Donner K., 2003. On the relation between the photoactivation energy and the absorbance spectrum of visual pigments. Vision Research, accepted for publication.
dc.relation.haspart Ala-Laurila P., Donner K. and Koskelainen A., 2003. Thermal activation and photoactivation of visual pigments. Biophysical Journal, accepted for publication.
dc.subject.other Biotechnology en
dc.subject.other Physics en
dc.title The relation between spectral and thermal properties of vertebrate visual pigments en
dc.type G5 Artikkeliväitöskirja fi
dc.description.version reviewed en
dc.contributor.department Department of Engineering Physics and Mathematics en
dc.contributor.department Teknillisen fysiikan ja matematiikan osasto fi
dc.subject.keyword rhodopsin en
dc.subject.keyword photoreception en
dc.subject.keyword activation energy en
dc.subject.keyword thermal noise en
dc.subject.keyword spectral sensitivity en
dc.subject.keyword absorbance en
dc.subject.keyword vision en
dc.subject.keyword retina en
dc.identifier.urn urn:nbn:fi:tkk-001142
dc.type.dcmitype text en
dc.type.ontasot Väitöskirja (artikkeli) fi
dc.type.ontasot Doctoral dissertation (article-based) en
dc.contributor.lab Laboratory of Biomedical Engineering en
dc.contributor.lab Lääketieteellisen tekniikan laboratorio fi


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