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Robert E. Blankenship - One of the best experts on this subject based on the ideXlab platform.
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Microscopic and spectroscopic studies of untreated and Hexanol-treated chlorosomes from Chloroflexus aurantiacus
Biochimica et Biophysica Acta, 1995Co-Authors: B. L. Ramakrishna, Paula I. Van Noort, Robert E. BlankenshipAbstract:Abstract When isolated chlorosomes from Chloroflexus aurantiacus are treated with 1-Hexanol, the BChl cQy absorption band shifts from 740 to 670 nm, while the baseplate BChl a remains at 795 nm. The relative amount of BChl c in the 740 and 670 nm forms depends on the Hexanol concentration. Atomic force microscopy was used to study the ultrastructure of native, Hexanol-treated, and protein-free chlorosomes. Chlorosomes appeared to be larger and more rounded upon Hexanol treatment and did not return to the original shape or size after 2-fold dilution. Therefore, the Hexanol treatment is not completely reversible in terms of chlorosome structure. Untreated, Hexanol-treated and and Hexanol-treated and then diluted samples were investigated using steady-state and time-resolved fluorescence spectroscopy. For the sample treated with 68 mM Hexanol, a 24 ps energy transfer from BChl c to a was observed in the picosecond fluorescence measurements. After 2-fold dilution, most of the kinetic properties of the untreated chlorosomes, characterized by a major energy transfer component of 15 ps from BChl c 740 to BChl a 795, were regained. Energy transfer from either BChI c 740 or BChl c 670 to baseplate BChl a is fast and relatively efficient in untreated chlorosomes. In Hexanol-treated chlorosomes, the excited state lifetime is not very different from that in untreated samples, but the energy transfer efficiency is quite low. This may result from concentration quenching of the monomeric pigments in the Hexanol-treated Chorosomes.
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and spectroscopic studies of untreated and Hexanol-treated chlorosomes from Chloroflexus aurantiacus
1995Co-Authors: Paula I. Van Noort, Robert E. BlankenshipAbstract:When isolated chlorosomes from Chlorojlexus auruntiacus are treated with I-Hexanol, the BChl c Q, absorption band shifts from 740 to 670 nm, while the baseplate BChl a remains at 795 nm. The relative amount of BChl c in the 740 and 670 nm forms depends on the Hexanol concentration. Atomic force microscopy was used to study the ultrastructure of native, Hexanol-treated, and protein-free chlorosomes. Chlorosomes appeared to be larger and more rounded upon Hexanol treatment and did not return to the original shape or size after 2-fold dilution. Therefore, the Hexanol treatment is not completely reversible in terms of chlorosome structure. Untreated, Hexanol-treated and and Hexanol-treated and then diluted samples were investigated using steady-state and time-resolved fluorescence spectroscopy. For the sample treated with 68 mM Hexanol, a 24 ps energy transfer from BChl c to a was observed in the picosecond fluorescence measurements. After 2-fold dilution, most of the kinetic properties of the untreated chlorosomes, characterized by a major energy transfer component of 15 ps from BChl c 740 to BChl a 795, were regained. Energy transfer from either BChl c 740 or BChl c 670 to baseplate BChl a is fast and relatively efficient in untreated chlorosomes. In Hexanol-treated chlorosomes, the excited state lifetime is not very different from that in untreated samples, but the energy transfer efficiency is quite low. This may result from concentration quenching of the monomeric pigments in the Hexanol-treated chlorosomes.
James C. Liao - One of the best experts on this subject based on the ideXlab platform.
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Extending carbon chain length of 1-butanol pathway for 1-Hexanol synthesis from glucose by engineered Escherichia coli.
Journal of the American Chemical Society, 2011Co-Authors: Yasumasa Dekishima, Claire R. Shen, James C. LiaoAbstract:An Escherichia coli strain was engineered to synthesize 1-Hexanol from glucose by extending the coenzyme A (CoA)-dependent 1-butanol synthesis reaction sequence catalyzed by exogenous enzymes. The C4-acyl-CoA intermediates were first synthesized via acetyl-CoA acetyltransferase (AtoB), 3-hydroxybutyryl-CoA dehydrogenase (Hbd), crotonase (Crt), and trans-enoyl-CoA reductase (Ter) from various organisms. The butyryl-CoA synthesized was further extended to hexanoyl-CoA via β-ketothiolase (BktB), Hbd, Crt, and Ter. Finally, hexanoyl-CoA was reduced to yield 1-Hexanol by aldehyde/alcohol dehydrogenase (AdhE2). Enzyme activities for the C6 intermediates were confirmed by assays using HPLC and GC. 1-Hexanol was secreted to the fermentation medium under anaerobic conditions. Furthermore, co-expressing formate dehydrogenase (Fdh) from Candida boidinii increased the 1-Hexanol titer. This demonstration of 1-Hexanol production by extending the 1-butanol pathway provides the possibility to produce other medium chain l...
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extending carbon chain length of 1 butanol pathway for 1 Hexanol synthesis from glucose by engineered escherichia coli
Journal of the American Chemical Society, 2011Co-Authors: Yasumasa Dekishima, Claire R. Shen, Ethan I Lan, Kwang Myung Cho, James C. LiaoAbstract:An Escherichia coli strain was engineered to synthesize 1-Hexanol from glucose by extending the coenzyme A (CoA)-dependent 1-butanol synthesis reaction sequence catalyzed by exogenous enzymes. The C4-acyl-CoA intermediates were first synthesized via acetyl-CoA acetyltransferase (AtoB), 3-hydroxybutyryl-CoA dehydrogenase (Hbd), crotonase (Crt), and trans-enoyl-CoA reductase (Ter) from various organisms. The butyryl-CoA synthesized was further extended to hexanoyl-CoA via β-ketothiolase (BktB), Hbd, Crt, and Ter. Finally, hexanoyl-CoA was reduced to yield 1-Hexanol by aldehyde/alcohol dehydrogenase (AdhE2). Enzyme activities for the C6 intermediates were confirmed by assays using HPLC and GC. 1-Hexanol was secreted to the fermentation medium under anaerobic conditions. Furthermore, co-expressing formate dehydrogenase (Fdh) from Candida boidinii increased the 1-Hexanol titer. This demonstration of 1-Hexanol production by extending the 1-butanol pathway provides the possibility to produce other medium chain length alcohols using the same strategy.
Randolph M Beaudry - One of the best experts on this subject based on the ideXlab platform.
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Relationships between free and esterified fatty acids and LOX-derived volatiles during ripening in apple
Postharvest Biology and Technology, 2016Co-Authors: Carolina Contreras, Henrik Tjellström, Randolph M BeaudryAbstract:Ripening in intact apple fruit is accompanied by an increase in the autonomous emissions of Hexanol and esters derived from Hexanol (hexyl esters). It is thought that these compounds are, to some extent, dependent upon hexanal synthesis by the action of lipoxygenase (LOX) on fatty lipids. To better understand the relationship between fatty acid substrates and their volatile products, we determined the content of oleic (18:1), linoleic (18:2), and linolenic (18:3) acids in free and polar (esterified) lipid fractions of the skin and subtending cortex of ‘Jonagold’ fruit throughout ripening. In the free fatty acid fraction, 18:1 and 18:2 content increased several-fold during ripening, but the 18:3 content remained low and unchanged. In the polar lipid fraction, ripening resulted in a modest increase in the 18:1 and 18:2 content and an extensive decline in the 18:3 content. The rise in 18:2 content of the free fatty acid fraction mirrored emissions of Hexanol and hexyl esters in intact fruit and the decline in the 18:3 content of polar lipids reflected the drop in cis-3-hexenal emissions found for disrupted fruit tissue. For intact fruit, our results suggest that hexanal and its metabolites, Hexanol and hexyl esters, may be derived from the action of LOX on 18:2 free fatty acid. For disrupted fruit tissue, the data suggest cis-3-hexenal and trans-2-hexenal are largely generated from the action of LOX on 18:3 in the polar lipid fraction. The mechanism whereby free 18:1 and 18:2 could accumulate without a concomitant increase in free 18:3 is not clear. To our knowledge, there is currently no synthetic or catabolic pathway characterized that might account for this finding.
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Lipoxygenase-associated apple volatiles and their relationship with aroma perception during ripening
Postharvest Biology and Technology, 2013Co-Authors: Carolina Contreras, Randolph M BeaudryAbstract:Abstract Several important odor-active volatiles are produced via processes initiated by cellular disruption brought about by cutting or mastication. Of these, six-carbon (C6) volatiles, including the aldehydes, cis -3-hexenal, its isomer trans -2-hexenal, and hexanal, as well as their corresponding alcohols, are produced from action of the lipoxygenase (LOX) pathway on substrates released by tissue disruption. We investigated the production of these and other odor-active volatiles from ‘Jonagold’ apple fruit for whole and disrupted tissues as a function of maturity/ripeness. The impact of ripening was determined by comparing ‘normally-ripening’ fruit with ‘non-ripening’ (1-methylcyclopropene-treated) fruit. The study was conducted over 8 weeks and evaluations were twice-weekly for two successive seasons. C6 aldehyde synthesis by crushed fruit was, at first, extremely high for non- and normally-ripening fruit such that the concentration of the aldehydes was several hundred times higher than their human odor thresholds in the containers used to present samples to the sensory panelists. cis -3-Hexenal, which remained constant throughout the experiment for non-ripening fruit, declined markedly for normally-ripening fruit, coincident with the onset of ripening. Conversely, trans -2-hexenal and hexanal increased in normally-ripening fruit as ripening progressed. Hexanol and hexyl acetate and other esters were produced in a ripening-dependent manner for disrupted as well as intact fruit tissues. The exception was cis -3-hexenyl acetate, which had same declining pattern as its aldehyde precursor, cis -3-hexenal. PCA determined that all volatiles except cis -3-hexenal, cis -3-hexenol and cis -3-hexenyl acetate, were highly associated with ripening. Also, cis -3-hexenal and cis -3-hexenyl acetate correlated negatively with all other variables (volatiles, ethylene, CO 2 and sensory tests). Sensory tests revealed that panelists were able to distinguish between non-ripening and normally-ripening fruit approximately 2 weeks before the onset of autocatalytic ethylene, the respiratory climacteric, and ripening-dependent ester production of normally-ripening fruit. The data indicate a shift in LOX pathway activity occurs during ripening, but it is not clear if it is due to changing enzyme activities or changing substrate levels. The shift in pathway activity may be related to perceived changes in aroma for macerated fruit prior to autocatalytic ethylene production.
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effect of hexanal vapor on spore viability of penicillium expansum lesion development on whole apples and fruit volatile biosynthesis
Journal of Food Science, 2006Co-Authors: Jun Song, Randolph M Beaudry, P D HildebrandAbstract:The effects of hexanal vapor on spore viability of Penicillium expansum, lesion development on whole apple fruit, and flavor volatile biosynthesis were investigated. Spore viability was reduced by 94% after exposure to a hexanal concentration of 40 μmol/L for 24 h, compared with 50% at 18 μmol/L and 20% at 9 μmol/L. Decay on whole apple fruit inoculated with 5 × 104 spores/mL of P. expansum was reduced with exposure to hexanal vapor for 48 h. Although almost all of the fruit treated with 8 to 12 jmiol/L developed decay lesions, lesion size was reduced compared with the controls. At concentrations of 15 to 19 μmol/L, and 25 to 29 μmol/L, the incidence of fruit with lesions was 44% and 24%, respectively, compared with 100% and 98% in the inoculated control apples and lesion size was further reduced. Apples treated at 4°C with only 5 to 7 jimol/L hexanal vapor also showed a marked reduction in lesion incidence. Hexanal was rapidly converted to high levels of the aroma volatiles Hexanol, hexylacetate, hexylbutanoate, and hexylhexanoate, but these decreased to levels similar to the control after 4 to 7 d of being held in air. There was no detectable hexanal after holding fruit in air for 5 h.
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Hydroperoxide Lyase Activity Necessary for Normal Aroma Volatile Biosynthesis of Tomato Fruit, Impacting Sensory Perception and Preference
HortScience, 2005Co-Authors: Mauricio Canoles, Marisol Soto, Randolph M BeaudryAbstract:The aldehydes cis-3-hexenal, hexanal, and trans-2-hexenal; the alcohols 1-Hexanol, and cis-3-hexenol; and the ketone 1-penten-3-one are produced as a consequence of lipid degradation following tissue disruption and are among the most important volatile compounds in tomato (Lycopersicon esculentum Mill.) aroma. The biosynthesis of cis-3-hexenal and other volatiles noted involves the action of a sequence of enzymes including lipase, lipoxygenase (LOX), hydroperoxide lyase (HPL), isomerase, and alcohol dehydrogenase (ADH) on glycerolipids containing the fatty acids, linoleic acid (18:2) and linolenic acid (18:3), via the LOX pathway. In the current work, the formation and sensory perception of volatile compounds was studied in tomato plant lines where HPL activity was genetically altered. LeHPL co-suppression dramatically reduced the production of lipid-derived C6-volatiles in leaves, but in fruits, only unsaturated C6-volatile production was affected, suggesting LeHPL-independent formation of hexanal occurs in fruits, but not in leaves. Increased production of 5-carbon volatiles is proposed as an alternative way to metabolize 13-hydroperoxy linolenic acid in plants with reduced LeHPL activity. Changes in the volatile profile of leaves and fruits of tomato lines in which LeHPL activity is reduced markedly are readily detected by nontrained sensory panels. The studies demonstrate that a marked reduction in the activity of one of the most critical steps in the LOX pathway can markedly impact sensory perception. Efforts to improve total volatile formation may require the modification of LOX pathway at several steps simultaneously, including precursor formation, and LOX and HPL activities.
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HEXANAL VAPOR ACTS AS RESIDUELESS ANTIFUNGAL AGENT THAT ENHANCES AROMA BIOSYNTHESIS IN APPLE FRUIT
Acta Horticulturae, 1998Co-Authors: Jun Song, Weimin Deng, R. Leepipattwit, Randolph M BeaudryAbstract:Hexanal vapor inhibited hyphal growth of Penicillium expansum Link, and Botrytis cinerea Pers, on PDA media and on apple slices. After 48 hours exposure to 100 μl.liter -1 (ppm) hexanal, the hyphal growth of both fungi was approximately 50% that of untreated controls. At a concentration of 250 μl.liter -1 (ppm), neither fungus grew during the treatment period; however, some growth of both fungi occurred 120 hours after treatment. At concentrations of hexanal vapor of 450 μl.liter -1 (ppm) or more, the growth of both fungi ceased and the organisms were apparently killed, neither showing regrowth when moved to air. When fungi were allowed to germinate and grow for 48 hours in hexanal-free air, a subsequent 48-hour exposure to 250 μl.liter -1 (ppm) hexanal slowed colony growth relative to controls for several days and a 48-hour exposure to 450 μl.liter -1 (ppm) stopped growth completely. Concentrations of hexanal that inhibited fungal growth on PDA also retarded decay lesion development on 'Golden Delicious' and on 'Jonagold' apple slices. Hexanal treatment stimulated aroma volatile production in 'Jonagold' and 'Golden Delicious' apple slices with Hexanol and hexylacetate production strongly enhanced after 20-30 hrs of treatment. A small amount of butylhexanoate and hexylhexanoate production was also noted.
Werner Kunz - One of the best experts on this subject based on the ideXlab platform.
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Bio-oxidation of n-Hexanol by alcohol oxidase and catalase in biphasic and micellar systems without solvent.
Biotechnology and Bioengineering, 2003Co-Authors: Maha Karra-chaabouni, Sylviane Pulvin, Daniel Thomas, Didier Touraud, Werner KunzAbstract:Alcohol oxidase from Pichia pastoris together with catalase from bovine liver was used to oxidize n-Hexanol to hexanal. For this purpose, an aqueous buffer solution was mixed with large amounts of Hexanol by simple agitation, yielding a biphasic system, or by adding the nonionic surfactant Brij 35. Initial velocities and reaction yields after 24 h were measured as a function of various parameters such as the amounts of enzymes, Hexanol, or surfactant. High enzymatic activity was determined for Hexanol concentrations of between 20 mass% and 80 mass% without using any additional organic solvent. The homogenization of the biphasic systems with the help of Brij 35 did not yield a significant improvement of the bioconversion, which would justify the use of surfactants.
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Biooxidation of n-Hexanol by alcohol oxidase and catalase in biphasic and micellar systems without solvent.
Biotechnology and Bioengineering, 2002Co-Authors: Maha Karra-chaabouni, Sylviane Pulvin, Daniel Thomas, Abdelghani Meziani, Didier Touraud, Werner KunzAbstract:Alcohol oxidase from Pichia pastoris together with catalase from bovine liver was used to oxidize n-Hexanol to hexanal. For this purpose, an aqueous buffer solution was mixed with large amounts of Hexanol by simple agitation, yielding a biphasic system, or by adding the nonionic surfactant Brij 35. Initial velocities and reaction yields after 24 h were measured as a function of various parameters such as the amounts of enzymes, Hexanol, or surfactant. High enzymatic activity was determined for Hexanol concentrations of between 20 mass% and 80 mass% without using any additional organic solvent. The homogenization of the biphasic systems with the help of Brij 35 did not yield a significant improvement of the bioconversion, which would justify the use of surfactants.
Ignacio Moreno-villoslada - One of the best experts on this subject based on the ideXlab platform.
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Aggregation Number in Water/n-Hexanol Molecular Clusters Formed in Cyclohexane at Different Water/n-Hexanol/Cyclohexane Compositions Calculated by Titration 1H NMR
Journal of Physical Chemistry B, 2017Co-Authors: Mario E. Flores, Toshimichi Shibue, Natsuhiko Sugimura, Hiroyuki Nishide, Ignacio Moreno-villosladaAbstract:Upon titration of n-Hexanol/cyclohexane mixtures of different molar compositions with water, water/n-Hexanol clusters are formed in cyclohexane. Here, we develop a new method to estimate the water and n-Hexanol aggregation numbers in the clusters that combines integration analysis in one-dimensional 1H NMR spectra, diffusion coefficients calculated by diffusion-ordered NMR spectroscopy, and further application of the Stokes–Einstein equation to calculate the hydrodynamic volume of the clusters. Aggregation numbers of 5–15 molecules of n-Hexanol per cluster in the absence of water were observed in the whole range of n-Hexanol/cyclohexane molar fractions studied. After saturation with water, aggregation numbers of 6–13 n-Hexanol and 0.5–5 water molecules per cluster were found. O–H and O–O atom distances related to hydrogen bonds between donor/acceptor molecules were theoretically calculated using density functional theory. The results show that at low n-Hexanol molar fractions, where a robust hydrogen-bond...
