Vision photoreceptor membranes

In connection with the problem of oscillations discussed by previous speakers and other types of dynamical behavior of membranes, it would probably be timely to mention here in some more detail the experiments with vision rhodopsin that were performed in our institute by using the Mossbauer spectroscopy method [G. R. Kalamkarov et al., Doklady Biophys., 219, 126 (1974)]. These experiments manifested the existence of reversible photo-induced conformational changes in the photoreceptor membrane even at such low temperature as 77°K. We have labeled various samples of solubilized rhodopsin and of photoreceptor membranes by iron ascorbate enriched with Fe57 and looked for the change of Mossbauer spectra caused by the illumination of our samples. 

Stryer L 1986 Cyclic GMP cascade of vision Anna. Rev. Neurosci. 9 87-119 Cafiso D S and Hubbell W L 1980 Light-induced interfacial potentials in photoreceptor membrane Biophys. J. 30 243-63 Drain C M, Christensen B and Mauzerall D 1989 Photogating of ionic currents across a lipid bilayer Proc. Natl Acad. Sci. USA 86 6959-62 Vsevolodov N N, Druzhko A B and Djukova T V 1989 Actual possibilities of bacteriorhodopsin application Molecular Electronics Biosensors and Biocomputers ed F T Hong (New York Plenum) pp 381-4 Vsevolodov N N and Dyukova T V 1994 Retinal-protein complexes as optoelectronic components Trend. Biotechnol. 12 81-103 Vsevolodov N N, Djukova T V and Druzhko A B 1989 Some methods for irreversible write-once recording in Biochrom films Proc. Annu. Int. Conf IEEE Eng. Med. Biol. Soc. 11 1327... 

Suzuki, T., Narita, K., Yoshihara, K., Nagai, K., and Kito, Y, Phosphatidyl inositol-phospholipase C in squid photoreceptor membrane is activated by stable metarhodopsin via GTP-binding protein Gq, Vision Res., 35,1995, p. 1011. 

Rhodopsin is a seven ot-helix trans-membrane protein and visual pigment of the vertebrate rod photoreceptor cells that mediate dim light vision. In this photoreceptor, retinal is the chromophore bound by opsin protein, covalently linked to Lys296 by a Schiff base linkage. Kpega et al.64 have studied NMR spectra of Schiff bases being derivatives of all-frans retinal and amino-p-cyclodextrins as a model of rhodopsin, where p-cyclodextrin plays a role of a binding pocket. On the basis of analysis of the chemical shift differences for the model compound in the presence and in the absence of adamantane carboxylate, it has been shown that the derivative of 3-amino-p-cyclodextrin forms dimer in water and retinoid is inserted into p-cyclodextrin cavity [31]. 

The process of vision begins in the photoreceptor outer segment, where light is absorbed by the photopigment (rhodopsin) to produce a cascade of reactions within the receptor (Stryer, 1986). Rhodopsin contains a membrane-bound opsin (protein) and a light-... 

DHA is very abundant in excitable membranes in the retina and brain, particularly in PL of the rod outer segment of retina and of synaptic vesicles, and is important in vision. However, the mechanism by which DHA functions in retina is not well understood. Chen et al. (Y. Chen, 1993) suggest that DHA in retina might be involved in shuttling 11-c/j-retinal to photoreceptors, whereas Niu et al. (S. Niu, 2004) propose that DHA in PL increases the efficiency of G-protein-mediated signal transduction of rhodopsin. In humans, supplementation of infant formula with DHA accelerates the development of visual functions in pre-term infants. The novel protective lipid mediator docosanoids, namely, Protectin D1 (C. Serhan, 2002) and 17S-hydroperoxy-DHA (V. Marcheselli, 2003), have been suggested to mediate the beneficial effects of DHA. 

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. 

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