Visual pigment

The study of visual pigment analogs serves to clarify the nature of chromophore-opsin interactions in visual pigments. Visual pigment analogs are modified retinals bound to opsins, which can be investigated by spectroscopic and biochemical methods. 

Figure 32.28. Evolutionary Relationships among Visual Pigments. Visual pigments have evolved by gene duplication along different branches of the animal evolutionary tree. The branch lengths of the "trees" correspond to the percentage of amino acid divergence. [Adapted from Nathans, J. Neuron 24(1999) 299 by permission of Cell Press.]...

Schoenlein R W, Peteanu L A, Wang Q, Mathles R A and Shank C V 1993 Femtosecond dynamics of cis-trans Isomerization In a visual pigment analog Isorhodopsin J. Phys. Chem. 97 12 087-92... 

The quantitative measurement of pigment or pigmented system deterioration upon exposure to heat or light used to be expressed by visual numerical standards. In modem times color differences are expressed in the CIELAB system which has become the leading method for color characterization (8). 

The stmcture of vitamin A [11103-57-4] and some of the important derivatives are shown in Figure 1. The parent stmcture is aH-Zra/ j -retinol [68-26-8] and its lUPAC name is (all-E)-3,7-dimethyl-9-(2,6,6-trimethyl-l-cyclohexen-l-yl)-2,4,6,8-nonatetraen-l-ol (1). The numbering system for vitamin A derivatives parallels the system used for the carotenoids. In older Hterature, vitamin A compounds are named as derivatives of trimethyl cyclohexene and the side chain is named as a substituent. For retinoic acid derivatives, the carboxyl group is denoted as C-1 and the trimethyl cyclohexane ring as a substituent on C-9. The stmctures of vitamin A and -carotene were elucidated by Karrer in 1930 and several derivatives of the vitamin were prepared by this group (5,6). In 1935, Wald isolated a substance found in the visual pigments of the eye and was able to show that this material was identical with Karrer s retinaldehyde [116-31-4] (5) (7). 

Natural Sensitizing Dyes and Photodynamic Therapy. The chlorophylls are, of course, among the natural sensitizers for photosynthesis. Considerable iaterest exists ia chlorophyll and related pigments as photosensitizers ia biology and medicine (75), isomeric retinal chromophores as visual pigments (76,77), and the use of synthetic photosensitizers ia neurobiology (9), hematology (78), and photodynamic therapy (79). 

The objective indication of color differences in foods has usually been attempted in a simplified, indirect way that involves a comparison of some physical characteristic of the samples or, more often, an extracted fraction that is assumed or has been proved to be largely responsible for the associated color characteristics. Although such a method does not measure the actual visual color of the samples, a measure of relative amounts of color-characteristic pigments or a comparison of physical properties of extracts of color-critical fractions (which may be mixtures of several pigments) may prove to be very sensitive indications of differences that are closely related to color. 

Hiller-Adams, P., Widder, E. A., and Case, J. F. (1988). The visual pigments of four deep-sea crustacean species. J. Comp. Physiol. 163A 63-72. 

A Retinol, p-carotene Visual pigments in the retina regulation of gene expression and cell differentiation p-carotene is an antioxidant Night blindness, xerophthalmia keratinization of skin... 

BARTLEY G E and SCOLNIK P A (1995) Plant carotenoids pigments for photoprotection, visual attraction, and hmnan health . Plant Cell, 7, 1027-38. 

First, a food quahty relationship model has been developed. It considers food quahty (FQ) to be dependent on food behavior (FB) and human behavior (HB). FB is a function of food dynamics (FD) (such as variable pigment concentrations and differing color degradahon prohles) and apphed technological conditions (TCs) (such as oxygen control to maintain color concentrahons). Likewise, HB is a function of human dynamics (HD) (for example, varying color perceptions due to age differences), and administrative conditions (ACs) (such as use of color cards to support visual color inspection). These relations are reflected in the food quahty relationship model as ... 

The retina comprises two principal components, the non-neural retinal pigment epithelium and the neural retina. The retinal pigment epithelium is an essential component of the visual system both structurally and functionally. It is important for the turnover and phagocytosis of photoreceptor outer segments, the metabolism of retinoids, the exchange of nutrients between the photoreceptors, and the choroidal blood vessels and the maintenance of an efficient outer blood-retinal barrier. 

Additional side effects have been noted in some women. Women with contact lenses may have visual changes and more disturbances with lenses. If normal saline eye drops do not help, referral to an ophthalmologist is recommended. Melasma and chloasma can occur secondary to estrogen stimulation of melanocyte production. Women with darker pigmentation are more susceptible. The melasma may not be... 

The vertebrate retina contains two classes of light-sensitive receptor cells called rods and cones. The rod is an elongated cylindrical cell containing several hundred thylakoids which support the visual pigment. The pigment system in the rod is confined to internal membranes situated close to the outer membrane of the cell. In the other type of visual receptor, the cone, the pigment is situated in the external membrane itself. In the cone the external... 

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