. Carotenoids, their comparative biochemistry. Carotenoids. CAROTENOIDS As realized by Steven, there is no reason why fish should absorb astacin under any conditions. As was pointed out in Chapter V(see^. 170) this is an artefact produced by oxidation of an astaxanthin and under natural conditions fish would never be presented with it. Steven's suggestion that failure to absorb lutein might be due to a similar reason cannot be easily upheld ; with careful handling in extracting this pigment from plant materials the only possible change it is likely to undergo is cis-trans isomerization, and it
. Carotenoids, their comparative biochemistry. Carotenoids. CAROTENOIDS As realized by Steven, there is no reason why fish should absorb astacin under any conditions. As was pointed out in Chapter V(see^. 170) this is an artefact produced by oxidation of an astaxanthin and under natural conditions fish would never be presented with it. Steven's suggestion that failure to absorb lutein might be due to a similar reason cannot be easily upheld ; with careful handling in extracting this pigment from plant materials the only possible change it is likely to undergo is cis-trans isomerization, and it is well known that cis isomers of xanthophylls which are vitamin A precursors {, crypto- xanthin) are absorbed by rats and still possess some vitamin activity. ^ • There is one report that the (? carotenoid) pigmentation of Esox lucius is also of alimentary origin. * ° 0-7 EryChrophore Xanthophore. 400 450 500 550 Wavcleno!:'] (mp) Fig. 27.—The absorption spectra of single Chromatophores of the trout {Salmo trutta). (From Steven, D. M. {1948) J. Exp. Biol., 25, 369.) Function (i) In Phototropic Responses Goodrich, Hill, and Arrick^^ examining a number of fresh water tropical fish showed that the xanthophylls, lutein, zeaxanthin, and taraxanthin were all concentrated in the xanthophores. The erythro- phore pigment was not a carotenoid but a pterin-like pigment which 206. Please note that these images are extracted from scanned page images that may have been digitally enhanced for readability - coloration and appearance of these illustrations may not perfectly resemble the original Goodwin, T. W. (Trevor Walworth). New York, Chemical Pub. Co.
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