Photoreceptor molecules

For directional responses, the photoreceptor molecules (or an array of those) are necessarily — at least for the duration of the photoreaction — located in a matrix with a fixed orientation to the bending organelle, or to the whole body of freely swimming organisms. 

Such an ordered organization of biological photoreceptor molecules appears to be a common feature (which, of course, is hardly detected in more opaque, highly scattering biological material). In the vertebrate rod maximum absorption lies in membranes (discs) perpendicular to the long axis of the rods, but anisotropically within these planes47). 

Minamoto T, Shimizu I 2002 A novel isoform of vertebrate ancient opsin in a smelt fish, Plemglossus altivelis. Biochem Biophys Res Commun 290 280—286 Miyashita Y, Moriya T, Yamada K et al 2001 The photoreceptor molecules in Xenopus tadpole tail fin, in which melanophores exist. Zoolog Sci 18 671—674 Moriya T, Miyashita Y, Arai J, Kusunoki S, Abe M, Asami K 1996 Light-sensitive response in melanophores of Xenopus laevis I. Spectral characteristics of melanophore response in isolated tail fin of Xenopus tadpole. J Exp Zool 276 11-18 Moutsaki P, Bellingham J, Soni BG, David-Gray ZK, Foster RG 2000 Sequence, genomic structure, and tissue expression of carp (Cyprinus carpio L.) vertebrate ancient (VA) opsin. FEES Lett 473 316-322... 

Ahmad M, Grancher N, Heil M et al 2002 Action spectrum for cryptochrome-dependent hypocotyl growth inhibition in Arabidopsis. Plant Physiol 129 774-785 Bellingham J, Whitmore D, Philp AR, Wells DJ, Foster RG 2002 Zebrafish melanopsin isolation, tissue localisation and phylogenetic position. Brain Res Mol Brain Res 107 128-136 Crawford BH 1949 The scotopic visibility function. Proc Phys Soc Lond B62 321—334 Miyashita Y, Moriya T, Yamada K et al 2001 The photoreceptor molecules in Xenopus tadpole tail fin, in which melanophores exist. Zool Sci 18 671-674 Wald G 1945 The spectral sensitivity of the human eye a spectral adaptometer. J Opt Soc Am 35 187... 

The third mechanism (3) is the simplest one. When trans-cis photoisomerizable chromophores are incorporated into the polymer backbone, the photoinduced configuration change of the chromophores is expected to induce a conformation change of the polymer chain. Azobenzene (4) is the most widely used as the trans-cis photoisomerizable photoreceptor molecule. It undergoes isomerization from the trans to the cis form under ultraviolet irradiation, while the cis form can return to the trans form either thermally or photochemically [11]. 

The fourth mechanism (4) invokes the electrostatic repulsion between photogenerated charges as the driving force for conformation changes. Triphenylmethane leucoderivatives (72) have been used as photoreceptor molecules. The chromophore dissociates into an ion-pair under ultraviolet irradiation, generating an intensely green colored triphenylmethyl cation. The cation thermally recombines the counter anion as follows. 

In the process of vision, light is absorbed by photoreceptor molecules like rhodopsin followed by a formation of several intermediate products (Fig. 14). Rhodopsin consists of an 11-cis retinal chromophore and opsin, a protein. After the absorption of a photon the 11-cis bond of retinal is transformed into a 11-trans bond. 

Photoreceptor Molecules in the Eye Detect Visible Light (Text Section 32.3)... 

The photoreceptor molecules used by different microorganisms for light perception vary significantly and fall in different classes including BLUE proteins, cryptochromes, phototropins, phytochromes, and rhodopsins. Other prokaryotic and eukaryotic organisms use photoactive yellow proteins (PYP) which contain a 4-hydroxycinnamate chromophore (21)., chlorophylls, carotenoids, phycobilins, and pterins. Hypericins have been found to be involved in photoorientation of ciliates (22). 

Chlorophylls are the green pigments that act as the principal photoreceptor molecules of plants. They are capable of absorbing certain wavelengths of visible light that are then converted by plants into chemical energy. Two forms of these pigments... 

Triphenylmethane leuco derivatives are well-known photochromic molecules that dissociate into ion pairs under UV irradiation, prodncing intensely colored triphenylmethyl cations. The cations thermally recombine with connter ions as above. Triphenylmethane leuco derivatives have been widely used as photoreceptor molecules. 

Chlorophyll is the photoreceptor molecule that traps this most elusive of all powers . It is found in the chloroplasts of green plants, and is what makes green plants, green. 

The property changes of the chromophores, such as dipole moment and/or geometrical structural changes, have been successfully utilized as a driving force to induce a conformational change of the polymer chain, when the chromophores are incorporated into the polymer as "photoreceptor molecules". 

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