Search results for "xanthophylls"
showing 10 items of 22 documents
Supplementary Ultraviolet-B Radiation Induces a Rapid Reversal of the Diadinoxanthin Cycle in the Strong Light-Exposed DiatomPhaeodactylum tricornutu…
2002
AbstractA treatment of the diatom Phaeodactylum tricornutum with high light (HL) in the visible range led to the conversion of diadinoxanthin (Dd) to diatoxanthin (Dt). In a following treatment with HL plus supplementary ultraviolet (UV)-B, the Dt was rapidly epoxidized to Dd. Photosynthesis of the cells was inhibited under HL + UV-B. This is accounted for by direct damage by UV-B and damage because of the UV-B-induced reversal of the Dd cycle and the associated loss of photoprotection. The reversal of the Dd cycle by UV-B was faster in the presence of dithiothreitol, an inhibitor of the Dd de-epoxidase. Our results imply that the reversal of the Dd cycle by HL + UV-B was caused by an incre…
Degradation of Carotenoids in Apricot (Prunus armeniaca L.) During Drying Process
2013
"Carotenoids are natural compounds whose nutritional importance comes from the provitamin A activity of some of them and their protection against several serious human disorders. The degradation of carotenoids was investigated during apricot drying by microwave and convective hot-air at 60 and 70 A degrees C. Seven carotenoids were identified: antheraxanthin, lutein, zeaxanthin, beta-cryptoxanthin, 13-cis-beta-carotene, all-trans-beta-carotene and 9-cis-beta-carotene; among these, all-trans-beta-carotene was found to be about 50 % of total carotenoids. First-order kinetic models were found to better describe all-trans-beta-carotene reduction during drying, with a degradation rate constant (…
Kinetics of carotenoids degradation and furosine formation in dried apricots (Prunus armeniaca L.)
2017
Abstract The kinetics of carotenoid and color degradation, as well as furosine formation, were investigated in apricot fruits during convective heating at 50, 60 and 70 °C. Degradation of carotenoids and color, expressed as total color difference (TCD), followed a first and zero order kinetic, respectively. The activation energy (Ea) for carotenoids degradation ranged from 73.7 kJ/mol for 13- cis -β-carotene to 120.7 kJ/mol for lutein, being about 91 kJ/mol for all- trans -β-carotene. Violaxanthin and anteraxanthin were the most susceptible to thermal treatment. The furosine evolution was fitted at zero order kinetic model. The Ea for furosine formation was found to be 83.3 kJ/mol and the Q…
The influence of phase transitions in phosphatidylethanolamine models on the activity of violaxanthin de-epoxidase
2008
In the present study, the influence of the phospholipid phase state on the activity of the xanthophyll cycle enzyme violaxanthin de-epoxidase (VDE) was analyzed using different phosphatidylethanolamine species as model lipids. By using (31)P NMR spectroscopy, differential scanning calorimetry and temperature dependent enzyme assays, VDE activity could directly be related to the lipid structures the protein is associated with. Our results show that the gel (L beta) to liquid-crystalline (L alpha) phase transition in these single lipid component systems strongly enhances both the solubilization of the xanthophyll cycle pigment violaxanthin in the membrane and the activity of the VDE. This pha…
Immune activation rapidly mirrored in a secondary sexual trait.
2003
A crucial assumption underlying most models of sexual selection is that sexual advertisements honestly reflect the phenotypic and/or genetic quality of their bearers ([1][1]). Here we show that experimental activation of the immune system is rapidly mirrored in the expression of a carotenoid-based
Inverse association of vitamin C with cataract in older people in India.
2011
OBJECTIVE: To examine the association between vitamin C and cataract in the Indian setting. DESIGN: Population-based cross-sectional analytic study. PARTICIPANTS: A total of 5638 people aged ≥60 years. METHODS: Enumeration of randomly sampled villages in 2 areas of north and south India to identify people aged ≥60 years. Participants were interviewed for socioeconomic and lifestyle factors (tobacco, alcohol, household cooking fuel, work, and diet); attended a clinical examination, including lens photography; and provided a blood sample for antioxidant analysis. Plasma vitamin C was measured using an enzyme-based assay in plasma stabilized with metaphosphoric acid, and other antioxidants wer…
Lipid dependence of diadinoxanthin solubilization and de-epoxidation in artificial membrane systems resembling the lipid composition of the natural t…
2006
In the present study, the solubility and enzymatic de-epoxidation of diadinoxanthin (Ddx) was investigated in three different artificial membrane systems: (1) Unilamellar liposomes composed of different concentrations of the bilayer forming lipid phosphatidylcholine (PC) and the inverted hexagonal phase (H(II) phase) forming lipid monogalactosyldiacylglycerol (MGDG), (2) liposomes composed of PC and the H(II) phase forming lipid phosphatidylethanolamine (PE), and (3) an artificial membrane system composed of digalactosyldiacylglycerol (DGDG) and MGDG, which resembles the lipid composition of the natural thylakoid membrane. Our results show that Ddx de-epoxidation strongly depends on the con…
Role of hexagonal structure-forming lipids in diadinoxanthin and violaxanthin solubilization and de-epoxidation
2005
In this study, we have examined the influence of different lipids on the solubility of the xanthophyll cycle pigments diadinoxanthin (Ddx) and violaxanthin (Vx) and on the efficiency of Ddx and Vx de-epoxidation by the enzymes Vx de-epoxidase (VDE) from wheat and Ddx de-epoxidase (DDE) from the diatom Cyclotella meneghiniana, respectively. Our results show that the lipids MGDG and PE are able to solubilize both xanthophyll cycle pigments in an aqueous medium. Substrate solubilization is essential for de-epoxidase activity, because in the absence of MGDG or PE Ddx and Vx are present in an aggregated form, with limited accessibility for DDE and VDE. Our results also show that the hexagonal st…
De-epoxidation of Violaxanthin after Reconstitution into Different Carotenoid Binding Sites of Light-harvesting Complex II
2001
In higher plants, the de-epoxidation of violaxanthin (Vx) to antheraxanthin and zeaxanthin is required for the pH-dependent dissipation of excess light energy as heat and by that process plays an important role in the protection against photo-oxidative damage. The de-epoxidation reaction was investigated in an in vitro system using reconstituted light-harvesting complex II (LHCII) and a thylakoid raw extract enriched in the enzyme Vx de-epoxidase. Reconstitution of LHCII with varying carotenoids was performed to replace lutein and/or neoxanthin, which are bound to the native complex, by Vx. Recombinant LHCII containing either 2 lutein and 1 Vx or 1.6 Vx and 1.1 neoxanthin or 2.8 Vx per mono…
Combined dynamics of the 500–600 nm leaf absorption and chlorophyll fluorescence changes in vivo: Evidence for the multifunctional energy quenching r…
2021
Carotenoids (Cars) regulate the energy flow towards the reaction centres in a versatile way whereby the switch between energy harvesting and dissipation is strongly modulated by the operation of the xanthophyll cycles. However, the cascade of molecular mechanisms during the change from light harvesting to energy dissipation remains spectrally poorly understood. By characterizing the in vivo absorbance changes (Delta A) of leaves from four species in the 500-600 nm range through a Gaussian decomposition, while measuring passively simultaneous Chla fluorescence (F) changes, we present a direct observation of the quick antenna adjustments during a 3-min dark-to-high-light induction. Underlying…