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Title: Xanthophylls as metabolic precursors
Author: Davies, Bethan Wyn
ISNI:       0000 0004 2698 6517
Awarding Body: Aberystwyth University
Current Institution: Aberystwyth University
Date of Award: 1986
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Studies were undertaken to investigate the role of xanthophylls (particularly zeaxanthin and lutein) as precursors of other carotenoids and related compounds in some species of yeast, fish and birds. In goldfish ß-carotene, lutein, zeaxanthin and canthaxanthin were shown by radiolabelling experiments to be precursors of retinol and 3,4-didehydroretinol. All these carotenoids except lutein, were metabolised to astaxanthin in goldfish integument. Turkey retinal oil droplet carotenoids were investigated and in some cases the absolute configurations defined e. (3R)galloxanthin, (3R, 6'S) α-cryptoxanthin, astaxanthin (66% 3S, 3'S-, 30% meso-, 4% 3R, 3'R, zeaxanthin (72% 3R, 3'R-, 28% meso-), epilutein (46% 3R,6'S, 3'R-, 54% 3S, 6'S, 3'R-) and lutein (50% 3R, 6'R, 3'R-, 3R6'S,3'S-). A new carotenoid structure is proposed for a retinal oil droplet carotenoid. Chick retinal oil droplet carotenoids were qualitatively similar to turkey carotenoids. 3,4-Didehydrotetinol, detected in chicken liver extracts, was not of dietary origin. The lutein and zeaxanthin of poultry feed were of plant origin i.e. (3R,6'R,3'R)lutein and (3R,3'R) zeaxanthin. Zeaxanthin was shown by radiolabelling experiments in chick embryos, to be the precursor of astaxanthin galloxanthin, E-galloxanthin and α-cryptoxanthin. The conversion of zeaxanthin to E,E-carotene was not clearly defined.  Zeaxanthin was deposited in chick feathers, intestine and livers during embryonic development, zeaxanthin and lutein being the major carotenoids present in these tissues. Chick embryo experiments were carried out with [2-14C]MVA as substrate to investigate whether or not de novo synthesis of carotenoids was possible in embryonic animal tissue.  Low levels of radioactivity in the carotenoid zones subject these results to some doubt. Microspectrophotometric studies on turkey oil droplets demonstrated that a mixture of carotenoids was present in each type of oil droplet. The same oil droplet types were present in turkey as in chicken and pigeon. Previous work in the laboratory suggested that Phaffia rhodozyma metabolised zeanthin and canthaxanthin to astaxanthin.  This had stereochemical implications. These metabolic transformations could not be demonstrated.
Supervisor: Davies, B. H. Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available