Microspectrophotometry of visual pigments

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Abstract
Visual pigments are embedded in the disc membranes of the outer segments of vertebrate rods and cones and in the microvilli of invertebrate visual cells. The pigment molecule in both is a most fascinating aggregate of known (the ubiquitous II-cisisomer of vitamin A1or A2-aldehyde = retinal1or2; Hubbard & Wald, 1952) covalently bonded to the unknown (a protein termed opsin) (Anderson, Hoffman & Hall, 1971). This conjugated molecule is called rhodopsin or dehydrorhodopsin (porphryopsin) when the prosthetic portion is retinall or 2 respectively. So sensitive is this sterically hindered, bent and twisted molecule to light that absorption of one photon can initiate its isomerization to the alltransform. This conformational change is but one (but the best known) of the factors leading to receptor membrane changes ushering in the visual impulse.