Signaling states of rhodopsin: absorption of light in active metarhodopsin II generates an all-trans-retinal bound inactive state.
Absorption of light in rhodopsin leads through 11-cis- and all-trans-retinal isomerization, proton transfers, and structural changes to the active G-protein binding meta-II state. When meta-II is photolysed by blue light absorption, the activating pathway is apparently reverted, and rhodopsin is photoregenerated. However, the product formed, a P subspecies with A(max) = 500 nm (P(500)), is different from the ground state based on the following observations: (i) the ground state fingerprint of 11-cis-retinal does not appear in the infrared spectra, although the proton transfers and structural changes are reverted; (ii) extraction of the retinal from P(500) does not yield the expected stoichiometric amount of 11-cis-retinal but predominantly yields all-trans-retinal; (iii) the infrared spectrum of P(500) is similar to the classical meta-III intermediate, which arises from meta-II by thermal decay; and (iv) both P(500) and meta-III can be photoconverted to meta-II with the same changes in the infrared spectrum and without a significant change in the isomerization state of the extracted chromophore. The data indicate the presence of a "second switch" between active and inactive conformations that operates by photolysis but without isomerization around the C(11)-C(12) double bond. This emphasizes the exclusivity of the ground state, which is only accessible by the metabolic regeneration with 11-cis-retinal.
Bartl
F J
FJ
Institute for Medical Physics and Biophysics, Medizinische Fakultät Charité, Humboldt University, Schumann Strasse 20-21, 10098 Berlin, Germany.
Ritter
E
E
Hofmann
K P
KP
D002851:Chromatography, High Pressure Liquid; D008027:Light; D008954:Models, Biological; D008956:Models, Chemical; D011485:Protein Binding; D011522:Protons; D012243:Rhodopsin / Q000031:analogs & derivatives / Q000737:chemistry* / Q000378:metabolism*; D015398:Signal Transduction; D013053:Spectrophotometry; D013237:Stereoisomerism; D013997:Time Factors
D011522:Protons; C013110:metarhodopsins; D012243:Rhodopsin