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Retina, Retinol, Retinal and the Natural History of Vitamin A as a Light Sensor
Department of Physiology, Jules Stein Eye Institute, and Howard Hughes Medical Institute, David Geffen School of Medicine, University of California, Los Angeles, CA 90095, USA
* Author to whom correspondence should be addressed.
Received: 1 November 2012; in revised form: 27 November 2012 / Accepted: 28 November 2012 / Published: 19 December 2012
Abstract: Light is both the ultimate energy source for most organisms and a rich information source. Vitamin A-based chromophore was initially used in harvesting light energy, but has become the most widely used light sensor throughout evolution from unicellular to multicellular organisms. Vitamin A-based photoreceptor proteins are called opsins and have been used for billions of years for sensing light for vision or the equivalent of vision. All vitamin A-based light sensors for vision in the animal kingdom are G-protein coupled receptors, while those in unicellular organisms are light-gated channels. This first major switch in evolution was followed by two other major changes: the switch from bistable to monostable pigments for vision and the expansion of vitamin A’s biological functions. Vitamin A’s new functions such as regulating cell growth and differentiation from embryogenesis to adult are associated with increased toxicity with its random diffusion. In contrast to bistable pigments which can be regenerated by light, monostable pigments depend on complex enzymatic cycles for regeneration after every photoisomerization event. Here we discuss vitamin A functions and transport in the context of the natural history of vitamin A-based light sensors and propose that the expanding functions of vitamin A and the choice of monostable pigments are the likely evolutionary driving forces for precise, efficient, and sustained vitamin A transport.
Keywords: vitamin A; retinoid; opsins; retina; retinol; retinal; STRA6; retinol binding protein
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Zhong, M.; Kawaguchi, R.; Kassai, M.; Sun, H. Retina, Retinol, Retinal and the Natural History of Vitamin A as a Light Sensor. Nutrients 2012, 4, 2069-2096.
Zhong M, Kawaguchi R, Kassai M, Sun H. Retina, Retinol, Retinal and the Natural History of Vitamin A as a Light Sensor. Nutrients. 2012; 4(12):2069-2096.
Zhong, Ming; Kawaguchi, Riki; Kassai, Miki; Sun, Hui. 2012. "Retina, Retinol, Retinal and the Natural History of Vitamin A as a Light Sensor." Nutrients 4, no. 12: 2069-2096.