title: Studies on structure and function of rhodopsin by use of cyclopentatrienylidene 11-cis-locked-rhodopsin.
abstract: The photochemical reaction of cyclopentatrienylidene 11-cis-locked-rhodopsin derived from cyclopentatrienylidene 11-cis-locked-retinal and cattle opsin was spectrophotometrically studied. The difference absorption spectrum between the cyclopentatrienylidene 11-cis-locked-rhodopsin and its retinal oxime had its maximum at 495 nm (P-495). Irradiation of P-495 at -196 degrees C with either blue light or orange light caused no spectral change, supporting the cis-trans isomerization hypothesis for formation of bathorhodopsin. Upon irradiation of P-495 at 0 degree C with orange light, however, its absorption spectrum shifted to a shorter wavelength owing to formation of a hypsochromic product. The difference absorption spectrum between this product (P-466) and its retinal oxime showed its maximum at 466 nm. Analysis of retinal isomers by high-performance liquid chromatography showed that this spectral shift was not accompanied by photoisomerization of the chromophore. P-466 could almost completely be photoconverted to the original pigment (P-495) by irradiation at 0 degree C with blue light with little formation of the other isomeric form of its chromophore. The alpha-band of the circular dichroism spectrum of P-495 was very small in comparison with that of rhodopsin, while that of P-466 was comparable to it. These facts suggest that P-495 has a planar conformation in the side chain of the chromophore and that P-466 has a twisted one, probably at the C8-C9 single bond. Cyclic-GMP phosphodiesterase in frog rod outer segment was activated by neither P-495 nor P-466. This result suggests that the isomerization of the retinylidene chromophore of rhodopsin is indispensable in the phototransduction process.
mesh_terms: D015106:3',5'-Cyclic-GMP Phosphodiesterases / Q000378:metabolism; D000818:Animals; D002417:Cattle; D002942:Circular Dichroism; D003080:Cold Temperature; D003517:Cyclopentanes / Q000378:metabolism / Q000494:pharmacology / Q000528:radiation effects; D004789:Enzyme Activation / Q000187:drug effects; D005136:Eye Proteins / Q000378:metabolism; D007536:Isomerism; D007700:Kinetics; D008027:Light; D010777:Photochemistry; D012168:Retinal Pigments / Q000502:physiology*; D012243:Rhodopsin / Q000031:analogs & derivatives / Q000378:metabolism / Q000494:pharmacology / Q000502:physiology* / Q000528:radiation effects; D012374:Rod Cell Outer Segment / Q000201:enzymology; D017299:Rod Opsins; D013053:Spectrophotometry
chemical_list: D003517:Cyclopentanes; D005136:Eye Proteins; D012168:Retinal Pigments; D017299:Rod Opsins; D012243:Rhodopsin; D015106:3',5'-Cyclic-GMP Phosphodiesterases