459 resultados para Carotenoids


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Carotenoids are important biomolecules that are ubiquitous in nature and find widespread application in medicine. In photosynthesis, they have a large role in light harvesting (LH) and photoprotection. They exert their LH function by donating their excited singlet state to nearby (bacterio)chlorophyll molecules. In photosynthetic bacteria, the efficiency of this energy transfer process can be as low as 30%. Here, we present evidence that an unusual pathway of excited state relaxation in carotenoids underlies this poor LH function, by which carotenoid triplet states are generated directly from carotenoid singlet states. This pathway, operative on a femtosecond and picosecond timescale, involves an intermediate state, which we identify as a new, hitherto uncharacterized carotenoid singlet excited state. In LH complex-bound carotenoids, this state is the precursor on the reaction pathway to the triplet state, whereas in extracted carotenoids in solution, this state returns to the singlet ground state without forming any triplets. We discuss the possible identity of this excited state and argue that fission of the singlet state into a pair of triplet states on individual carotenoid molecules constitutes the mechanism by which the triplets are generated. This is, to our knowledge, the first ever direct observation of a singlet-to-triplet conversion process on an ultrafast timescale in a photosynthetic antenna.

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Carotenoids in the photosynthetic membranes of plants typically contain two β-rings (e.g., β-carotene and zeaxanthin) or one ɛ- and one β-ring (e.g., lutein). Carotenoids with two ɛ-rings are uncommon. We reported earlier that the Arabidopsis thaliana lycopene ɛ-cyclase (LCYe) adds one ɛ-ring to the symmetrical linear substrate lycopene, whereas the structurally related lycopene β-cyclase (LCYb) adds two β-rings. Here we describe a cDNA encoding LCYe in romaine lettuce (Lactuca sativa var. romaine), one of the few plant species known to accumulate substantial quantities of a carotenoid with two ɛ-rings: lactucaxanthin. The product of the lettuce cDNA, similar in sequence to the Arabidopsis LCYe (77% amino acid identity), efficiently converted lycopene into the bicyclic ɛ-carotene in a heterologous Escherichia coli system. Regions of the lettuce and Arabidopsis ɛ-cyclases involved in the determination of ring number were mapped by analysis of chimeric ɛ-cyclases constructed by using an inverse PCR approach. A single amino acid was found to act as a molecular switch: lettuce LCYe mutant H457L added only one ɛ-ring to lycopene, whereas the complementary Arabidopsis LCYe mutant, L448H, added two ɛ-rings. An R residue in this position also yields a bi-ɛ-cyclase for both the lettuce and Arabidopsis enzymes. Construction and analysis of chimera of related enzymes with differing catalytic activities provide an informative approach that may be of particular utility for studying membrane-associated enzymes that cannot easily be crystallized or modeled to existing crystal structures.

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The production of pigments by halophilic archaea has been analysed during the last half a century. The main reasons that sustains this research are: (i) many haloarchaeal species possess high carotenoids production availability; (ii) downstream processes related to carotenoid isolation from haloarchaea is relatively quick, easy and cheap; (iii) carotenoids production by haloarchaea can be improved by genetic modification or even by modifying several cultivation aspects such as nutrition, growth pH, temperature, etc.; (iv) carotenoids are needed to support plant and animal life and human well-being; and (v) carotenoids are compounds highly demanded by pharmaceutical, cosmetic and food markets. Several studies about carotenoid production by haloarchaea have been reported so far, most of them focused on pigments isolation or carotenoids production under different culture conditions. However, the understanding of carotenoid metabolism, regulation, and roles of carotenoid derivatives in this group of extreme microorganisms remains mostly unrevealed. The uses of those haloarchaeal pigments have also been poorly explored. This work summarises what has been described so far about carotenoids production by haloarchaea and their potential uses in biotechnology and biomedicine. In particular, new scientific evidence of improved carotenoid production by one of the better known haloarchaeon (Haloferax mediterranei) is also discussed.

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Literature cited: p. 23-33.

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Few Micronesian foods have been analyzed for nutrient content. Information is needed on locally grown, culturally acceptable foods that could be promoted to alleviate, vitamin A deficiency in the Federated States of Micronesia. Using an ethnographic approach that included key informant interviews and observation, Micronesian cultivars with potential for high-carotenoid content according to their coloration were identified. These cultivars of banana, giant swamp taro, breadfruit and other foods were analyzed for alpha- and beta-carotene using high-performance liquid chromatography (HPLC) and for nine minerals using inductively coupled plasma (ICP). A wide range of provitamin A carotenoid levels was found in banana, taro, and breadfruit cultivars, some containing very high levels (beta-carotene content from 515 to 6360 mug/100 g in banana, 260 to 1651 mug/100 g in taro, and 295 to 868 mug/100 g in breadfruit, edible portion). Other cultivars contained moderate levels, but as they can be eaten in large quantities, they may contribute significantly to vitamin A status. The taro samples contained very high levels of zinc (mean 5.9 mg/100 g) and significant levels of other minerals (mean content of calcium was 120 mg/100 g). These staples with cultural acceptability and high availability potentially could play a role in vitamin A, micronutrient, and chronic disease programs in the Pacific. (C) 2003 Elsevier Science Ltd. All rights reserved.

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Commonly recommended plant sources of provitamin A, such as dark green leafy vegetables, are not acceptable in many population groups. The objective of this study was to identify other indigenous foods that may be effectively promoted to alleviate vitamin A deficiency (VAD) and to gather information relevant to identification, production, acquisition, and consumption of foods relevant to a food-based VAD prevention strategy in the Federated States of Micronesia. An ethnographic study on edible pandanus cultivars, involving key informant interviews and observation was carried out. Analyses revealed a great range in carotenoid content. Several orange-coloured pandanus cultivars, all highly acceptable, contained high levels of carotenoid, almost meeting daily requirements in usual consumption patterns, whereas light yellow-coloured cultivars contained low levels. Availability has decreased substantially in recent years due to increased consumption of imported foods and general neglect of indigenous foods. High-carotenoid pandanus should be promoted for general enjoyment and health benefits.

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Vitamin A deficiency (VAD) and chronic diseases are serious problems in the Federated States of Micronesia and other Pacific island countries. Nutrition education programs to address these in Micronesia have had limited success, partly due to lack of information on nutrient content in local foods. The study objective was to identify local plant foods rich in provitamin A and other carotenoids that have high levels of cultural acceptability. Food cultivars likely to be carotenoid-rich (suggested by coloration) were identified using an ethnographic approach including key informant interviews. Raw and cooked samples (mostly cultivars previously not analyzed) of 12 banana, 13 giant swamp taro, 10 breadfruit cultivars and four other local foods were analyzed by high-performance liquid chromatography. Many banana and taro cultivars were found with significant levels of beta- and alpha-carotene; the beta-carotene levels ranged from 30 to 2780 mug/100 g (banana) and. 50 to 2040 mug/100 g (taro). The results highlight the potential significance of cultivar differences in human nutrition, important for evaluation of the diet, establishment of locally relevant dietary guidelines, and research on the relationship between diet, health, and disease. These highly acceptable food cultivars could play an important role in VAD and chronic disease prevention programs in the Pacific. (C) 2003 Elsevier Science Ltd. All rights reserved.

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Recently very potent extracorporeal cholesterol-lowering treatment options have become available for patients with hypercholesterolemia. LDL immunoapheresis treatment selectively removes LDL and lipoprotein(a) from the circulation. Since LDL is the major carrier of lipophilic antioxidants in plasma, the purpose of the present study was to assess the effects of a single LDL apheresis treatment on plasma concentrations of tocopherols (alpha- and gamma-tocopherol) and carotenoids (alpha- and beta-carotene, zeaxanthin, cryptoxanthin, canthaxanthin, lycopene, and retinol). Plasma antioxidant concentrations were determined by HPLC in 7 patients with familial hypercholesterolemia before and after LDL immunoapheresis treatment. Plasma concentrations of both alpha- and gamma-tocopherol and the different carotenoids were significantly reduced by LDL apheresis. However, when standardized for cholesterol to adjust for cholesterol removal, alpha- and gamma-tocopherol, retinol, and the more polar carotenoids lutein and zeaxanthin increased in response to apheresis treatment, while the more unpolar carotenoids such as beta-carotene and lycopene did not change. These data demonstrate that a single LDL immunoapheresis treatment affects tocopherols and individual carotenoids differently. This may be explained by differences in chemical structure and preferential association with different lipoproteins. These results further imply that tocopherols, lutein, zeaxanthin, and retinol, are associated in part with lipoproteins and other carriers such as retinol-binding protein that are not removed during apheresis treatment. (C) 2004 Wiley-Liss, Inc.

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Background: Epidemiologic evidence suggests that serum carotenoids are potent antioxidants and may play a protective role in the development of chronic diseases including cancers, cardiovascular disease, and inflammatory diseases. The role of these antioxidants in the pathogenesis of diabetes mellitus remains unclear. Objective: This study examined data from a cross-sectional survey to investigate the association between serum carotenoids and type 2 diabetes. Design: Study participants were adults aged >= 25 y (n = 1597) from 6 randomly selected cities and towns in Queensland, Australia. Study examinations conducted between October and December 2000 included fasting plasma glucose, an oral-glucose-tolerance test, and measurement of the serum concentrations of 5 carotenoid compounds. Results: Mean 2-h postload plasma glucose and fasting insulin concentrations decreased significantly with increasing quintiles of the 5 serum carotenoids-alpha-carotene, beta-carotene, beta-cryptoxanthin, lutein/zeaxanthin, and lycopene. Geometric mean concentrations for all serum carotenoids decreased (all decreases were significant except that of lycopene) with declining glucose tolerance status. beta-Carotene had the greatest decrease, to geometric means of 0.59, 0.50, and 0.42 mu mol/L in persons with normal glucose tolerance, impaired glucose metabolism, and type 2 diabetes, respectively (P < 0.01 for linear trend), after control for potential confounders. Conclusions: Serum carotenoids are inversely associated with type 2 diabetes and impaired glucose metabolism. Randomized trials of diets high in carotenoid-rich vegetables and fruit are needed to confirm these results and those from other observational studies. Such evidence would have very important implications for the prevention of diabetes.

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Objective: To evaluate responses to self-administered brief questions regarding consumption of vegetables and fruit by comparison with blood levels of serum carotenoids and red-cell folate. Design: A cross-sectional study in which participants reported their usual intake of fruit and vegetables in servings per day, and serum levels of five carotenoids (alpha-carotene, beta-carotene, beta-cryptoxanthin, lutein/zeaxanthin and lycopene) and red-cell folate were measured. Serum carotenoid levels were determined by high-performance liquid chromatography, and red-cell folate by an automated immunoassay system. Settings and subjects: Between October and December 2000, a sample of 1598 adults aged 25 years and over, from six randomly selected urban centres in Queensland, Australia, were examined as part of a national study conducted to determine the prevalence of diabetes and associated cardiovascular risk factors. Results: Statistically significant (P < 0.01) associations with vegetable and fruit intake ( categorised into groups: = 4 servings per day) were observed for alpha-carotene, beta-carotene, beta-cryptoxanthin, lutein/zeaxanthin and red-cell folate. The mean level of these carotenoids and of red-cell folate increased with increasing frequency of reported servings of vegetables and fruit, both before and after adjusting for potential confounding factors. A significant association with lycopene was observed only for vegetable intake before adjusting for confounders. Conclusions: These data indicate that brief questions may be a simple and valuable tool for monitoring vegetable and fruit intake in this population.