| Research Abstract |
Four types of chicken cone pigments, 2 types of visual pigment of nocturnal gecko and one types of pineal photoreceptive protein were determined amino acid sequences, the latter of which was named "Pinopsin" (lambdamax : 475nm) . On the basis of amino acid identities, the gecko pigments and pinopsin were regarded as cone-like pigments. Then, we constructed a phylogenetic tree of visual pigments, revealing that cone pigments evolved earlier than rod pigments (rhodopsins) and the pigment most closely situated to the ancestorial vertebrate visual pigment would be pinopsin. Thus color vision as well as photopic vision appeared earlier than scotopic vision. Conversions of cone pigments to rod pigments took place in the process of evolution by replacing basic amino acid residues with neutal and/or acidic ones. No significance difference in photosensitivity and primary process of photobleaching process between bovine rhodopsin and iodopsin was observed. A comparison in late bleaching process
… More
among bovine and chicken rhodopsins, chicken red and green and gecko pigments displayd that the rhodopsins are longer in life time of meta II intermediate than cone or cone-like pigments. The long life time would be favorable for activation of a great many molecules of transducin, and for conducting the high photosensitivity of rod comparing cone. Thus both the short life time meta II intermediate and basic protein would be necessary condition for cone pigments.
Histochemical and biochemical analyzes showed that chicken iodopsin is in both principal and accessory members of double cone and in a single cone with a red oil droplet, and that chicken green, blue and violet are located at single cones with yellow, clear and blue oil droplets, respectively. Since the oil droplet acts like a cut-off filter, the spectrum of iodopsin was corrected with transmittance curves of green oil droplet in the principal member and of the corresponding position in the accessory member without oil droplet, both the corrected spectra were close to chicken photopic sensitivity curve, which was recorded electrophysiologically, so that the double cone would be responsible for light intensity discrimination in daylight vision. The spectra of chicken red, green and blue were corrected by transmitance curves of the respective oil droplets, resulting in remarkable decrease of overlaps of two spectra between chicken red and blue and between chicken green and violet. Thus almost all the wave-lengths between 400 and 600 nm can be discriminated with ratios between absorptions by only two kinds of cone pigments. This fact would result in increase of the resolution of wavelength discrimination. Less
|
