Rhodopsin, irradiation

Fig. 2.162. Absorption spectra of Amphiopl expressed in HEK293s cells (a) and the HPLC patterns of retinal oximes (b). Absorption spectra and the HPLC patterns were measured before (a, curve 1, and b, top trace) and after irradiation at 520 nm for 2 min (a, curve 2, and b, middle trace). The HPLC pattern of retinal oximes extracted from a mixture of irradiated and non-irradiated bovine rhodopsin in equal amounts is indicated as a reference (b, bottom trace). The absorption maxima of the original pigment and its phoroproduct are shown in panel (a). Reprinted with permission from M. Koyanagi et al. [334].

FIGURE 28. 283-MHz 19F NMR spectra of isomers of 8-F-rhodopsin in CFIAPS before (lower) and after photoirradiation (upper) (a) 11-cis (pulse delay, D5 = 5.0 s, number of acquisitions, NA = 5200, line broadening, LB = 80 Hz) (b) 9-cis (D5 = 50 ms, NA = 160000, LB = 80 Hz). Disappearance of the excess 9-cis aldehyde was due to repeated formation and bleaching of pigment during the irradiation process. Reprinted with permission from Reference 48. Copyright (1996) American Chemical Society... 

In 1958, a new intermediate in the bleaching sequence of rhodopsin was discovered, the liquid air illuminated rhodopin [93]. This red-shifted transient (Amax =543 nm) could be observed when cattle rhodopsin was irradiated in aqueous-glycerol... 

Irradiation of rhodopsin with blue light (437 nm) at 77 K gave a photostationary mixture containing in addition to rhodopsin (33%) and isorhodopsin (16%) about 51 % of batho intermediate. This process was found to be thermally irreversible but photochemically reversible. Indeed, irradiation of bathorhodopsin with red light (> 650 nm) gave mainly rhodopsin and isorhodopsin. Irradiation of isorhodopsin, which contains a 9-cis chromophore, afforded the same batho product as the one obtained by irradiation of rhodopsin ... 

Fig. 10. Curve 1 A mixture of rhodopsin, isorhodopsin and bathorhodopsin produced by irradiation of rhodopsin with blue light (437 nm) at 77 K. Curves 2-6 Conversion of bathorhodopsin, to rhodopsin by irradiation with red light (X>650 nm) for 10, 10, 20, 40 and 80s. Curves 6-11 Conversion of bathorhodopsin2 to mainly rhodopsin by irradiation with red light (X>650 nm) for 80, 160. 320, 640, 1280 and 2560 s. From Sasaki et al. [59].

In an attempt to ascertain that bathorhodopsin is the earliest intermediate, the bleaching of cattle rhodopsin was investigated at liquid helium temperature (4 K). Irradiation at wavelengths longer than 530 nm gave a photostationary state contain-... 

Fig. I I. Absorption spectra of rhodopsin analog6 [150], (a) At 77 K. before irradiations, (b) After irradiation for 10 min with 460 nm light, (c) After a second irradiation of 10 min with 520 nm light. All of these spectra are superimposable. The two traces in the lower part of the figure are, respectively, the difference spectrum (expanded 10-fold) between curves (a) and (b) (top), and between curves (b) and (c) (bottom).

Data is also shown for bovine rhodopsin, 63, for comparison. The hydroretinals 66-68 presumably assume 9-cis or 11 -cis like conformations when bound to opsin. Retinals 67 and 68 form non-bleachable pigments, i.e., no change in their A, occurs upon exposure to room light irradiation by UV light leads to decomposition products instead of separation of the chromophore from opsin. a In MeOH. In case of split chromophores the absorption maxima of the enal moieties are given. b Protonated Schiff base with n-butylamine in MeOH. ... 

Retinoids. The 9,11-di-cw-isomer of retinaldehyde (90) has been prepared in six steps from the C15 aldehyde (93) and used to form a 9,11-di-m-rhodopsin with cattle opsin.60 The 9,1 l-di-cw-isomer was also one of four di-cis forms obtained by irradiation of all-fra/w-retinaldehyde in acetonitrile.61 The sterically hindered... 

Irradiation into this band caused photoisomerization, appreciable quantities of the 11-cw-isomer being formed. Several papers189-191 report calculations related to the spectroscopic properties of retinylidene Schiff bases. The principal absorption axes of rhodopsin and prelumirhodopsin have been determined.192 Photoacoustic Spectroscopy. The photoacoustic spectra of visual pigments have been reported.198... 

Using a mode-locked Nd + YAG laser system to generate picosecond sample excitation pulses and picosecond probing continuum pulses in their double beam spectrometer, Spalink et. al. (30) were able to measure difference absorption spectra of irradiated samples of 11-cis-rhodopsin and 9-cis-rhodopsin at selected times after excitation by means of a PAR OMA-2 optical multichannel detection system. The difference absorption spectral data were obtained over the entire spectral range from 410 nm to 650 nm at one time with an OMCD as opposed to the... 

They contain two pigments, rhodopsin and retinochrome. The two pigments have the same supramolecule (protein), have common chromophore retinal, but they differ in their bound chromophore stereochemistry (Scheme 13). Cephalopod rhodopsin has 11-cw-retinal as chromophore where as retinochrome has all-trans-retinal as chromophore [161,162], and when exposed to light they get interconverted (Scheme 13). [163]. More interestingly, the cephalopod leti-nochrome has been used to achieve one-way 11-cis isomerization induced by light. Retinal all-trans, 13-cis, and 9-cis isomers were mixed with retinochrome and irradiated at 390 nm to get specifically 11-cw-retinal (Scheme 14) [164,165]. 

The PC is actually the sum of two processes a fast component, which saturates only at extremely high irradiance levels and a slow component (69). The maximal amplitude amounts only to 10% of the fast component. The fast potential depends solely on the photoconversion rate of the photoreceptor and is the result of a localized calcium influx (67, 68). The late PC is driven by the transport of about 10 elementary charges across the membrane triggered by the absorption of approximately 10 photons. This means there is an amplification of about 10,000 (61). The amplification could be due to the activation of GTP in animal vision one excited rhodopsin can activate up to 500 G proteins, which in turn activate thousands of phosphodiesterase molecules. In Spermatozopsis evidence for the involvement of G-proteins in photoperception was presented (57, 58, 70). Light-dependent GTPase activity in isolated eyespot apparatuses was found with an action spectrum similar to that of rhodopsin absorption. 

In the dark retinal in rhodopsin is in the 11-cfs-configuration. Irradiation of rhodopsin leads to a series of conformational changes which can be noted by the disappearance and appearance of various intermediates of different colours. 

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