Rhodopsin absorption spectra

Figure 32.21 Rhodopsin absorption spectrum. Almost all photons with wavelengths near SOO nm that strike a rhodopsin molecule are absorbed.

The bleaching of rhodopsin has been found to lead to the all-trans form of retinal through several intermediate steps.(llb,45) These steps are temperature dependent consequently low temperatures must be used to observe the intermediate products. A solution of rhodopsin is subjected to a flash of light at liquid nitrogen temperature and intermediates are detected by changes in the absorption spectrum. The first intermediate, with an absorption maximum at 543 nm, believed to be an all-fra/w-retinal bound to opsin, has been termed prelumirhodopsin. Warming the sample to a temperature greater than... 

Figure 23-42 Absorption spectrum of cattle rhodopsin in aqueous dispersion with a nonionic detergent. From H. Shichi et a/.486 487...

Figure 5.12 Absorption spectrum of rhodopsin (full line) and sensitivity of the eye. The drop shown by the broken line is the absorption of the lens (L). Wavelength X in nmjlOO approximate colours shown as v (violet), b (blue), g (green), y (yellow) and r (red)...

In solution, 1 1-em-retinal absorbs maximally near 380 nm, but in rhodopsin the peak is at 500 nm (fig. S2.5). The absorption spectrum of rhodopsin is essentially identical to the spectrum of the sensitivity of the rod cells (after correction for absorption in the cornea and lens). The per-... 

Transformations of Rhodopsin Can Be Detected by Changes in Its Absorption Spectrum... 

Wald, et. al97,98. performed a set of experiments during the 1940 s that purported to demonstrate the formation of rhodopsin from either retinene, (now known as retinal) or Vitamin A, and a native protein. While their work involved materials showing a peak absorption at 500 nm, this is the wavelength of peak isotropic absorption of a large number of dipolar retinoids. Such a peak is not exclusive to the chromophoies of vision. Neither is it relevant to the anisotropic absorption spectrum of the chromophores of vision. 

Figure 5.5.10-5 CR Absorption spectrum of putative frog rhodopsin as a function of bleaching level. Curve 1 is unbleached. The material was prepared as a red powder and then placed in dilute solution. From Wolken, 1966. (A) Intrinsic ultraviolet peak of a retinoid. (B) intrinsic isotropic absorption peak of a retinol (al) complexed with opsin. From wolken, 1966.

Figure 5.5.10-5 CR Absorption spectrum of putative frog rhodopsin. 89...

Most current interest in u.v. spectra is concerned with retinal and its cis-trans isomers. Studies at 77 K include theoretical calculations, fluorescence, and the effect of protonation on the corresponding Schiff base. The singlet-triplet absorption spectrum of all-trans-retinol has been measured. Calculations on the absorption-emission spectra of rhodopsin suggest that there is little dependence on the angular twist in the polyene chain. Pulse radiolysis has made it... 

A visual pigment, rhodopsin, is mimicked by (29) [45]. (29) has an absorption maximum at 375 nm in its neutral form. However, the maximum shows a red shift of 100 - 120 nm on protonation of both the nitrogen atoms at low pH. The absorption spectrum of the diprotonated (29) is almost identical with that of native rhodopsin. Probably the retinal moiety of (29) is included in the cavity of cyclodextrin at low pH, resulting in the red shift due to a combination of an electrostatic effect and a microsolvent effect. 

The absorption spectrum of bathorhodopsin is known to have its maximum shifted to the red (A, ax m) of the normal dark-adapted rhodopsin (Xniax 00 Thus after excitation of rhodopsin with a 530 nm pulse, a probe pulse at 561 nm, which is within the absorption band of prelumirhodopsin, will encounter and display an absorption. Utilizing this known fact, Busch et al." excited rhodopsin at room temperature, with a 6 ps 530 nm pulse and measured the appearance of an absorption at 561 nm, which was interpreted as the formation of the first intermediate. The time constant of formation was found to be <6 ps, while the decay of the bathorhodopsin intermediate was measured to be — 50 ns. 

There are several other results that also support the proton-transfer mechanism. The absorption spectrum of bathorhodopsin is red shifted with respect to the spectrum of rhodopsin itself, therefore, bathorhodopsin may be a more tightly protonated Schiff base than rhodopsin. Model studies by Sandorfy " show explicitly that translocating the proton toward the Schiff base nitrogen could account for the spectral red shift. 

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. 

Electronic Absorption Spectroscopy. Doping with iodine and SO3 had a significant effect on the absorption spectrum of /3-carotene. Triplet-triplet absorption spectra have been obtained for six carotenoids, e.g. canthaxanthin carotene-4,4 -dione (181)] in benzene, " and bimolecular rate constants for energy transfer from singlet oxygen to carotenoids evaluated. U.v. spectra of retinal, retinyl acetate, and axerophtene (182) in solid films have been determined. Several papers discuss the light absorption spectra of retinal derivatives as rhodopsin models. ... 

Pig. 12. Simulated transient absorption spectrum as obtained for the two-mode model of the cis-trans isomerization in rhodopsin. The spectral band at 500 nm reflects the dynamics of the reactants, while the 570 nm band reflects the absorbance of the photoproducts. 

Fig. 2. Absorption spectrum of solubilized rhodopsin. Solid line before illumination, dotted line after illumination in the presence...

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