Search PubMed⌕ Search

Biomedical subjects

G Britton

Publications and source records attributed to G Britton.

At least 37 records · Page 2Linked to original sources
PubMed1984

Detection of carotenoids in blood donors taking Orobronze: a cautionary note.

During the summer, plasma samples from eight blood donors at this transfusion centre were found to have a bright orange colour. All donors appeared to be healthy and haematological tests showed no abnormality. Extracts of lipid from the plasma revealed the presence of the carotenoid canthaxanthin and other carotenoid metabolites which were identified by thin-layer chromatography and high-pressure liquid chromatography, light absorbtion and mass spectrometry. On questioning the donors it was found that they had been taking a course of 'Orobronze' (an oral 'bronzing' treatment containing canthaxanthin). Canthaxanthin was still detectable in the plasma several months after the donors had ceased taking the capsules. At present it seems that there would be no deleterious effects on healthy individuals taking orobronze. The full implications of the presence of canthaxanthin in plasma transfused to patients do, however, require further investigation of carotenoid metabolism in man.

Blood Donors↗
PubMed1981

Relation of glucose to alpha-fetoprotein in amniotic fluid.

A direct relationship between amniotic fluid glucose and alpha-fetoprotein (AFP) has been found between the 16th and 22nd weeks of pregnancy. This relationship is statistically significant (P less than .001) in each of the 6 gestational weeks tested, the coefficients of correlation vary from .74 to .91. The relationship between amniotic fluid AFP and another metabolite, urea nitrogen, was not significant (r = -.34), suggesting that the AFP-glucose relationship was not spurious. Absence of pregnancy-associated macroglobulins in the samples indicates that they were not contaminated by maternal serum. These data reflect an aspect of fetal metabolism or transport that should be investigated more thoroughly.

Amniotic Fluid↗
PubMed1978

Photosynthetic unit size, carotenoids, and chlorophyll-protein composition of Prochloron sp., a prokaryotic green alga.

Six samples of the prokaryotic, unicellular algae Prochloron sp., which occur in association with didemnid ascidians, were collected from various localities in the tropical Pacific Ocean, and their pigments and chlorophyll-protein complexes were identified and characterized. No phycobilin pigments were detected in any of the species. Chlorophylls a and b were present in ratios of a/b = 4.4-6.9. The major carotenoids were beta-carotene (70%) and zeaxanthin (20%). Minor carotenoids of one isolate were identified as echinenone, cryptoxanthin, isocryptoxanthin, mutachrome, and trihydroxy-beta-carotene; no epsilon-ring carotenoids were found in any sample. Except for the absence of glycosidic carotenoids, the overall pigment composition is typical of cyanobacteria. A chlorophyll a/b-protein complex was present in Prochloron; it was electrophoretically and spectrally indistinguishable from the light-harvesting chlorophyll a/b-protein of higher plants and green algae. It accounted for 26% (compared to approximately 50% in green plants) of the total chlorophyll; 17% was associated with a P700-chlorophyll a-protein. The photosynthetic unit size of 240 +/- 10 chlorophylls per P700 in Prochloron was about half that of eukaryotic green plants. A model is proposed for the in vivo organization of chlorophyll in Prochloron.

Journal Article↗
PubMed1977

The roles of isomers of phytoene, phytofluene and zeta-carotene in carotenoid biosynthesis by a mutant strain of Scenedesmus obliquus.

Considerable changes in pigment composition occur during a period of 10 h when dark-grown cultures of PG1, a zeta-carotenic strain of Scenedesmus obliquus, are illuminated. These changes are consistent with a biosynthetic pathway in which 15-cis-phytoene is converted via 15-cis-phytofluene and 15-cis-zeta-carotene into all-trans-zeta-carotene and trans-bicyclic carotenoids. The findings also support the view that the xanthophylls lutein and zeaxanthin are formed from the corresponding carotenes and are especially important in the development of a normal chloroplast structure.

Carotenoids↗
PubMed1977

Carotenoid biosynthesis in Rhodomicrobium vannielii. Experiments with nicotine and 2-(4-chlorophenylthio)triethylammonium chloride (CPTA).

Nicotine and 2-(4-chlorophenylthio)triethylammonium chloride (CPTA) each inhibit production of the normal carotenoids of Rhodomicrobium vannielii (Rhodospirillaceae), especially rhodopin, beta-carotene and spirillixanthin, and cause the accumulation of lycopene. The inhibition of hydration of the C-1,2 double bond as well as cyclization is in agreement with proposals that these two reactions involve similar mechanisms. After removal of nicotine, cells reincubated in buffer solution or in the presence of diphenylamine convert accumulated lycopene into rhodopin. Under other conditions rhodopis is synthesized, on removal of nicotine, not from accumulated lycopene but from early precursors. The pathway of rhodopin and spirilloxanthin biosynthesis in Rm. vannielii is discussed briefly, and the possible involvement of enzyme aggregates in carotenoid biosynthesis is considered.

Carotenoids↗
PubMed1977

A series of mutant strains of Scenedesmus obliquus with abnormal carotenoid compositions.

Several mutant strains of Scenedesmus obliquus (Chlorophyta) have been isolated which, when cultured heterotrophically, are pale green or yellow, in contrast to the dark green of the wild type. On the basis of their carotenoid compositions, four groups of pale-green strains have been delineated. These accumulate, respectively, no carotenoid, phytoene, mainly zeta-carotene and mainly zeta-carotene together with some neurosporene and lycopene. All these strains synthesized no chlorophyll b and only small amounts of chlorophyll a. A further group of yellow strains produced the normal Scenedesmus obliquus range of cyclic carotenes and xanthophylls, but no chlorophyll. Most of the pale-green strains were killed by exposure to light, but two strains, PG1 and 1E, which accumulated predominantly zeta-carotene when grown in the dark, survived exposure to the light and developed photosynthetically active chloroplasts containing the normal pigments. The possible biosynthetic implications of the carotenoid composition of these mutant strains, and the relationshp between the carotenoid composition and protection of the cells from photooxidative destruction are discussed.

Carotenoids↗
PubMed1977

The effect of illumination on the pigment composition of the zeta-carotenic mutant, PG1, of Scenedesmus obliquus.

Dark grown Scenedesmus obliquus strain PG1 accumulated zeta-carotene and phytoene as its major carotenoids. On illumination of dark-grown cultures in air/CO2, cyclic carotenes and xanthophylls were formed, apparently at the expense of the accumulated phytoene and zeta-carotene. This interconversion of carotenoids was accompanied by chlorophyll synthesis. In an atmosphere of nitrogen/CO2 the light-induced changes occurred more slowly and in nitrogen alone the changes were incomplete. No massive production of cyclic carotenes from the accumulated zeta-carotene was observed in cultures illuminated under anaerobic conditions.

Aerobiosis↗
PubMed1977

The carotenoids of Flavobacterium strain R1560.

The main carotenoid of Flavobacterium strain R1560 has been identified as (3R,3'R)-zeaxanthin. Also present were small amounts of 15-cis-phytoene, phytofluene, "zeta-carotene" (7,8,7',8'-tetrahydro-psi, psi-carotene plus 7,8,11,12-tetrahydro-psi, psi-carotene), neurosporene, lycopene, beta-zeacarotene, gamma-carotene, beta-carotene, beta-cryptoxanthin, rubixanthin, 3-hydroxy-beta-zeacarotene and several apo-carotenals. Zeaxanthin production was inhibited by nicotine (10 mM), and lycopene and rubixanthin accumulated. The biosynthesis of zeaxanthin is discussed in terms of pathways and also of "half-molecule" reaction sequences. The presence of zeaxanthin may be a characteristic of a group of Flavobacterium species, and may thus be useful in the taxonomic classification of these organisms.

Carotenoids↗
PubMed1974

Alternative pathways of zeaxanthin biosynthesis in a Flavobacterium species.

In Flavobacterium R1519, nicotine blocks zeaxanthin biosynthesis by specifically inhibiting the cyclization reaction. Lycopene (at high nicotine concentrations, e.g. 7.5mm) and rubixanthin (at low nicotine concentration, e.g. 1mm) replace zeaxanthin as the main carotenoid. On removal of the nicotine lycopene is converted into beta-carotene under anaerobic conditions and into zeaxanthin in the presence of O(2). The conversion in vivo of beta-carotene into zeaxanthin was also demonstrated. Cyclization (an anaerobic process) thus precedes hydroxylation (O(2)-requiring) in the biosynthesis of zeaxanthin. The conversion in vivo of rubixanthin into beta-cryptoxanthin and into zeaxanthin was demonstrated, thus indicating the operation of alternative pathways of zeaxanthin biosynthesis. Several alternative biosynthetic pathways are considered and the results are also discussed in terms of reaction sequences of carotenoid ;half-molecules'.

Carotenoids↗