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Structure and photobleaching process of chicken iodopsin
1Department of Information Systems Engineering, Faculty of Engineering, Osaka Sangyo University, Japan.
Biophysical Chemistry
|September 1, 1995
Summary
Chicken retinal iodopsin (a cone pigment) exhibits a red-shifted spectrum compared to rhodopsin. Its faster regeneration and decay rates explain the lower photosensitivity and rapid adaptation of cone cells.
Area of Science:
- Biochemistry
- Photochemistry
- Vision Science
Background:
- Iodopsin, the primary cone pigment in chicken retinas, possesses a longer wavelength absorption spectrum than rhodopsin.
- A proposed structural model suggested a greater distance between the protonated Schiff base nitrogen and counterion in iodopsin, accounting for its red-shifted spectrum.
Purpose of the Study:
- To investigate the photochemical properties of iodopsin and compare them with rhodopsin.
- To elucidate the structural basis for iodopsin's red-shifted absorption spectrum.
Main Methods:
- Resonance Raman spectroscopy was employed to confirm the structural model of iodopsin.
- Comparative studies of iodopsin and rhodopsin's photochemical properties, including regeneration rates and decay kinetics of signaling states.
Main Results:
- Resonance Raman spectroscopy confirmed the structural model of iodopsin, indicating a longer distance between the protonated Schiff base nitrogen and counterion.
- Iodopsin regenerated with 11-cis-retinal 240 times faster than rhodopsin.
- Meta-iodopsin II decayed approximately 100 times faster than meta-rhodopsin II, with a lower Km value for rhodopsin kinase.
Conclusions:
- The observed differences in regeneration and decay rates align with the rapid adaptation and lower photosensitivity characteristic of cone cells compared to rod cells.
- The structural and photochemical properties of iodopsin are finely tuned for cone-specific visual functions.