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Screening of lipases for the synthesis of xylitol monoesters by chemoenzymatic esterification and the potential of microwave and ultrasound irradiations to enhance the reaction rate

RUFINO, Alessandra R.; BIAGGIO, Francisco C.; SANTOS, Julio C.; CASTRO, Heizir F. de
Fonte: ELSEVIER SCIENCE BV Publicador: ELSEVIER SCIENCE BV
Tipo: Artigo de Revista Científica
ENG
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Lipases from different sources, Pseudomonas fluorescens (AK lipase), Burkholderia cepacia (PS lipase), Penicillium camembertii (lipase G) and Porcine pancreas lipase (PPL), previously immobilized on epoxy SiO(2)-PVA, were screened for the synthesis of xylitol monoesters by esterification of the protected xylitol using oleic acid as acyl donor group. Among all immobilized derivatives, the highest esterification yield was achieved by P. camembertii lipase, showing to be attractive alternative to bulk chemical routes to satisfy increasing commercial demands. Further experiments were performed to determine the influence of fatty acids chain size on the reaction yield and the feasibility of using non-conventional heating systems (microwave and ultrasound irradiations) to enhance the reaction rate. (C) 2010 Elsevier B.V. All rights reserved.; Fundacao de Amparo Pesquisa do Estado de Sao Paulo (FAPESP); Conselho Nacional de Desenvolvimento Cientifico e Tecnologico (CNPq)

Screening of Food Grade Lipases to be Used in Esterification and Interesterification Reactions of Industrial Interest

PAULA, Ariela Veloso de; NUNES, Gisele Fatima Morais; SILVA, Josiane de Lourdes; CASTRO, Heizir Ferreira de; SANTOS, Julio Cesar dos
Fonte: HUMANA PRESS INC Publicador: HUMANA PRESS INC
Tipo: Artigo de Revista Científica
ENG
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Seven food grade commercially available lipases were immobilized by covalent binding on polysiloxane-polyvinyl alcohol (POS-PVA) hybrid composite and screened to mediate reactions of industrial interest. The synthesis of butyl butyrate and the interesterification of tripalmitin with triolein were chosen as model reactions. The highest esterification activity (240.63 mu M/g min) was achieved by Candida rugosa lipase, while the highest interesterification yield (31%, in 72 h) was achieved by lipase from Rhizopus oryzae, with the production of about 15 mM of the triglycerides C(50) and C(52). This lipase also showed a good performance in butyl butyrate synthesis, with an esterification activity of 171.14 mu M/g min. The results demonstrated the feasibility of using lipases from C. rugosa for esterification and R. oryzae lipase for both esterification and interesterification reactions.; Fundacao de Amparo a Pesquisa do Estado de Sao Paulo (FAPESP); Conselho Nacional de Desenvolvimento Cientifico e Tecnologico (CNPq)

Niobium to alcohol mol ratio control of the concurring esterification and etherification reactions promoted by NbCl5 and Al2O3 catalysts under microwave irradiation

BARBOSA, Sandro L.; HURTADO, Gabriela R.; KLEIN, Stanlei I.; LACERDA JUNIOR, Valdemar; DABDOUB, Miguel J.; GUIMARAES, Carlos F.
Fonte: ELSEVIER SCIENCE BV Publicador: ELSEVIER SCIENCE BV
Tipo: Artigo de Revista Científica
ENG
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Alcohols and acids can be switched to produce ethers or esters by varying the alcohol to catalyst mol ratio, in a new etherification and esterification method using NbCl5/Al2O3 catalyst under ""solvent free"" conditions and promoted by MW (microwave) irradiation. A ""two sites"" mechanism for the reaction is proposed, in an attempt to clarify the tendency of the catalyst to be dependent on the alcohol alone during the esterification process. (c) 2008 Elsevier B.V. All rights reserved.

Modelagem cinética da esterificação de sec-butanol com ácido acético e estudo de monitoramento em linha da reação com espectroscopia de infravermelho.; Kinetic modeling of esterification of sec-butanol with acetic acid and study of reaction on-line monitoring using near infrared spectroscopy.

Dias, Marcio Andrade
Fonte: Biblioteca Digitais de Teses e Dissertações da USP Publicador: Biblioteca Digitais de Teses e Dissertações da USP
Tipo: Dissertação de Mestrado Formato: application/pdf
Publicado em 26/03/2012 PT
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A esterificação do sec-butanol com ácido acético, submetida à catálise homogênea, apresenta poucos resultados experimentais de cinética reacional e equilíbrio químico disponíveis na literatura. A presente dissertação visa determinar os parâmetros cinéticos e de equilíbrio químico desta reação de esterificação, empregando modelo cinético de 2ª ordem baseado em atividades. Os experimentos cinéticos foram realizados em reator batelada com auxílio da metodologia Karl Fischer para análise do teor de água e determinação do perfil de frações molares ao longo da reação. A principal dificuldade na modelagem desta esterificação consistiu em representar satisfatoriamente as não-idealidades da mistura em fase líquida, em espacial nas reações cuja fração molar inicial de ácido acético foi superior a 50%. Netas condições admitiu-se a ocorrência de dissociação do ácido acético levando ao surgimento de interações iônicas. O modelo empregado para obtenção das atividades, com base em frações molares, foi o NRTL. Este modelo representou bem as interações moleculares em condição de baixa acidez, mas apresentou desvios em condições de acidez e teores de água mais elevados. O estudo também visou o desenvolvimento de modelos de calibração para um método analítico on-line visando determinar o perfil de frações molares ao longo da reação. O método empregado foi a espectroscopia de infravermelho próximo (NIR)...

Niobium to alcohol mol ratio control of the concurring esterification and etherification reactions promoted by NbCl5 and Al2O3 catalysts under microwave irradiation

Barbosa, Sandro L.; Hurtado, Gabriela R.; Klein, Stanlei I.; Junior, Valdemar L.; Dabdoub, Miguel J.; Guimaraes, Carlos F.
Fonte: Elsevier B.V. Publicador: Elsevier B.V.
Tipo: Artigo de Revista Científica
ENG
Relevância na Pesquisa
366.73055%
Alcohols and acids can be switched to produce ethers or esters by varying the alcohol to catalyst mol ratio, in a new etherification and esterification method using NbCl5/Al2O3 catalyst under "solvent free" conditions and promoted by MW (microwave) irradiation. A "two sites" mechanism for the reaction is proposed, in an attempt to clarify the tendency of the catalyst to be dependent on the alcohol alone during the esterification process. (c) 2008 Elsevier B.V. All rights reserved.

Esterification of free fatty acids to biodiesel over heteropolyacids immobilized on mesoporous silica

Tropecêlo, A; Casimiro, M; Fonseca, I; Ramos, A; Vital, J; Castanheiro, Jose
Fonte: Elsevier Publicador: Elsevier
Tipo: Artigo de Revista Científica
POR
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Tungstophosphoric acid (PW), molybdophosphoric acid (PMo) and tungstosilicic acid (SiW) immobilized on SBA-15 were used, as catalysts, in the esterification of palmitic acid with methanol, at 60 ◦C. Catalysts were characterized by N2 adsorption, FTIR, X-ray diffraction, ICP-AES and TEM. All catalysts exhibited high catalytic activity in palmitic acid esterification with methanol. It was observed that the catalytic activity decreases in the follow series: PW1-SBA-15 > SiW-SBA-15 > PMo- SBA-15. A series of PW immobilized on SBA-15 with different PW loadings from 2.7 wt% to 8.3 wt% were prepared. It was observed high catalytic activity with low amount of tungstophosphoric acid immobilized on SBA-15. In order to optimize the reaction conditions, the effect of different parameters, such as catalyst loading, carbon length of the alcohol and temperature, molar ratio of fatty acid to methanol in the presence of PW3-SBA-15 were studied. PW3-SBA-15 catalyst can be separated from reaction system for re-use. It was observed a small leaching of the PW from SBA-15 to liquid phase. PW3-SBA-15 catalyst was also used in the esterification of stearic and oleic acid with methanol. High catalytic activity was observed.

Esterification of fatty acids to biodiesel over polymers with sulfonic acid groups

Caetano, CS; Guerreiro, L; Fonseca, I; Ramos, A; Vital, J; Castanheiro, JE
Fonte: Elsevier Publicador: Elsevier
Tipo: Artigo de Revista Científica
POR
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The esterification of palmitic acid with methanol was studied using poly(vinyl alcohol) cross-linked with sulfosuccinic acid (SSA) and polystyrene cross-linked with divinylbenzene with sulfonic acid groups, as catalysts, at 60 ºC. It was observed that the PVAmatrixes with sulfonic acid groups were more active than the polystyrene ones. With the most active polymeric matrix (PVA_SSA40), an almost 90% equilibrium conversion was achieved after 2 h. Further, the optimisation of reaction parameters, such as, catalyst loading, molar ratio alcohol to fatty acid and type of alcohol was carried out with PVA_SSA40 catalyst. Catalytic stability of the PVA_SSA40 was evaluated by performing consecutive batch runs with the same catalyst sample. After the second batch, a stabilisation of the catalytic activity was observed. The PVA_SSA40 was also used as catalyst in the esterification of oleic and stearic acid with methanol,having been obtained an equilibrium conversion of almost 80%. In order to become the biodiesel totally biogenerated, the esterification of palmitic acid was carried out with ethanol, at 60 ºC and 80 ºC. It was observed that the reaction rate is slower when the reaction is carried out with methanol, at 60 ºC. In a posterior catalytic experiment at 60 ºC...

Esterification of free fatty acids with methanol using heteropolyacids immobilized on silica

Caetano, C; Fonseca, I; Ramos, A; Vital, J; Castanheiro, Jose
Fonte: Elsevier Publicador: Elsevier
Tipo: Artigo de Revista Científica
POR
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369.95945%
The esterification of palmitic acid with methanol was studied using tungstophosphoric acid (PW), molibdophosphoric acid (PMo) and tungstosilicic acid (SiW) immobilized by sol–gel technique on silica, at 60 º C. It was observed that the catalytic activity decreases in the series: PW-silica > SiW-silica > PMo-silica. A series of PW immobilized on silica with different PW loadings from 2.5 wt.% to 8.4 wt.% were prepared. It was observed that the PW-silica2 (with 4.2 wt.%) shows the highest catalytic activity on esterification of palmitic acid with methanol. Catalytic stability of the PW-silica2 was evaluated by performing consecutive batch runs with the same catalyst sample. After the second batch it was observed a stabilisation of the initial activity. In order to study the heteropolyacid lixiviation, a posterior catalytic experiment was carried out. The PW-silica2 was put in contact with methanol, without palmitic acid, during 72 h. After this period, the catalyst was separated from methanol by centrifugation, and the palmitic acid was added to the reaction mixture. It was observed that the reaction only occurs in the heterogeneous phase. The PW-silica2 was also used as catalyst in esterification of others fatty acids: oleic and stearic acid. It was also observed a good catalytic activity of PW-silica2 for the different substrates used in the esterifications.

Esterification of free fatty acids over chitosan with sulfonic acid groups

Caetano, CS; Caiado, M; Ramos, A; Fonseca, I; Vital, J; Castanheiro, J
Fonte: Elsevier Publicador: Elsevier
Tipo: Artigo de Revista Científica
ENG
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Chitosan, which is an abundant biopolymer, with sulfonic acid groups was used as an efficient, environmentally friendly heterogeneous catalyst for the esterification of free fatty acids with methanol into their more fatty acid methyl ester. Sulfonic acid catalysts supported on chitosan have been studied in the esterification of palmitic acid with methanol at 60 C. The sulfonic acid groups were introduced onto chitosan (CT) through cross-linking with sulfosuccinic acid (SSA). The catalytic activity increased as the amount of sulfonic acid groups present in chitosan was increased. However, with large amounts of sulfonic acid groups, the catalytic activity decreased. This behaviour can be explained by the factors that limit the diffusion. The catalytic stability of the CT4 (2.08 mmol sulfonic acid groups/g) sample was evaluated through consecutive batch runs performed with the same catalyst sample. After the second batch, the catalytic activity stabilised. The CT4 catalyst was also used as a catalyst in the esterification of oleic and stearic acids with methanol. A good catalytic activity of CT4 for the different substrates used in the esterifications was observed.

Produção de lipases de Aspergillus niger e Aspergillus fumigatus através de fermentação em estado sólido, avaliação da especificidade do substrato e seu uso em reações de esterificação e alcoólise: evaluation of substrate specificity and use in esterification and alcoholysis reactions

Reinehr,Christian Oliveira; Rizzardi,Juliana; Silva,Marceli Fernandes; Oliveira,Débora de; Treichel,Helen; Colla,Luciane Maria
Fonte: Sociedade Brasileira de Química Publicador: Sociedade Brasileira de Química
Tipo: Artigo de Revista Científica Formato: text/html
Publicado em 01/06/2014 PT
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Filamentous fungi were cultured under solid state fermentation of soybean residues to produce lipases. Enzymes produced by Aspergillus niger esterified oleic and butyric acids in the presence of ethanol, while enzymes produced by Aspergillus fumigatus demonstrated no esterification activity toward lauric acid. In case of A. niger, direct lyophilization of fermented bran led to higher esterification activity. The esterification of oleic acid by enzymes of A. fumigatus was neither influenced by pH adjustment nor by the extraction process. Conversions to ethyl esters were higher after pH adjustment with lyophilized liquid extract of A. niger.

Synthesis, characterization and use of Nb2O5 based catalysts in producing biofuels by transesterification, esterification and pyrolysis

Brandão,Rodrigo F.; Quirino,Rafael L.; Mello,Vinicius M.; Tavares,André P.; Peres,Antônio C.; Guinhos,Flávia; Rubim,Joel C.; Suarez,Paulo A. Z.
Fonte: Sociedade Brasileira de Química Publicador: Sociedade Brasileira de Química
Tipo: Artigo de Revista Científica Formato: text/html
Publicado em 01/01/2009 EN
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Nb2O5/HX (X = HSO4-, H2PO4-, NO3-) compounds were obtained from the treatment of niobium acid (Nb2O5·xH2O) with sulfuric, phosphoric, and nitric acids as well as Nb2O5 and Nb2O5·xH2O have been investigated as catalysts for the transesterification, esterification and pyrolysis of vegetable oils. The compounds were characterized by thermal analysis (DTA-TGA), spectroscopy (DRX, FT-IR and FT-Raman), surface area (BET) and the acidity (Ho) determined by n-butylamine titration using the Hammet´s indicator method. It was observed that after the acid treatment both the surface area and the acidity decreased as compared to the starting Nb2O5·xH2O. The only exception was a higher acidity verified when nitric acid was used. Among the catalyst investigated, the Nb2O5/H3PO4 presented the highest activity in the alcoholysis of soybean oil with different mono-alcohols (methanol, ethanol, 2-propanol, n-butanol). All tested solids seemed to stabilize the carboxylic acids formed during the pyrolysis, yielding higher acid numbers for the obtained products. Finally, the use of Nb2O5/H3PO4 and Nb2O5/H2SO4 as catalysts for the esterification showed better activity than Nb2O5·xH2O and Nb2O5.

Layered metal laurates as active catalysts in the methyl/ethyl esterification reactions of lauric acid

Lisboa,Fábio da Silva; Gardolinski,José Eduardo F. da; Cordeiro,Claudiney S.; Wypych,Fernando
Fonte: Sociedade Brasileira de Química Publicador: Sociedade Brasileira de Química
Tipo: Artigo de Revista Científica Formato: text/html
Publicado em 01/01/2012 EN
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In this work we report the synthesis, characterization and investigation of the catalytic activity of layered copper(II), manganese(II), lanthanum(III) and nickel(II) laurates in the methyl and ethyl esterification reactions of lauric acid. In the methyl esterification, conversions between 80 and 90% were observed for all catalysts, while for the ethyl esterification only manganese laurate showed reasonable catalytic activity, with conversions close to 75%. Reuse of copper and lanthanum laurates in three cycles of reaction was also investigated and both catalysts preserved the structure and retained catalytic activity close to that observed for the first reaction cycle.

Preparation of ordered sulfonated mesoporous polymer (OMP-TsOH) from p-toluenesulfonic acid and application in esterification reaction of fatty acids

Shokrolahi,Arash; Zali,Abbas; Pouretedal,Hamid Reza; Mousaviazar,Ali
Fonte: Sociedade Brasileira de Química Publicador: Sociedade Brasileira de Química
Tipo: Artigo de Revista Científica Formato: text/html
Publicado em 01/06/2012 EN
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366.73055%
Sulfonated ordered mesoporous polymer was simply prepared by co-mixing p-formaldehyde, p-toluenesulfonic acid (p-TsOH) and sulfuric acid. SBA-15 and/or MCM-48 mesoporous silicas were used as templates. High specific surface area and acid density of the novel solid acids were obtained in the range 900-1400 m² g-1 and of 4.9 mmol g-1, respectively. Catalysts prepared with SBA-15 template presented higher pore diameter, and the use of the MCM-48 template is due to higher specific surface area. The catalytic activities of the solid acids were studied in oleic acid esterification reaction. The initial rates of the solid acids with templates of SBA-15 and MCM-48 were 80-93 and 62-80 µmol min-1, respectively. Catalyst with higher pore diameter showed the higher initial rate of esterification reaction and higher conversion efficiency of oleic acid. Consequently, the pore diameter played a crucial role in catalytic activity.

Ethyl oleate production by means of pervaporation-assisted esterification using heterogeneous catalysis

Figueiredo,K. C. S.; Salim,V. M. M.; Borges,C. P.
Fonte: Brazilian Society of Chemical Engineering Publicador: Brazilian Society of Chemical Engineering
Tipo: Artigo de Revista Científica Formato: text/html
Publicado em 01/12/2010 EN
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Pervaporation-assisted esterification of oleic acid and ethanol was investigated by means of heterogeneous acid catalysis with the aim of increasing the ethyl oleate yield. The experimental strategy comprised kinetic tests with Amberlyst 15 Wet (Rohm & Haas), the characterization of hydrophilic Pervap 1000 membrane (Sulzer) and the evaluation of the membrane-assisted reactor. Kinetic tests were carried out to study the effect of temperature, catalyst loading and ethanol/organic acid molar ratio for the esterification of oleic acid and ethanol. The ester yield and initial reaction rate were used as response. The hydrophilic poly(vinyl alcohol) membrane was able to remove water from the reaction medium and, hence, the ester yield was increased. The potential of coupling esterification and pervaporation was demonstrated, with a two-fold increase in the reaction yield of ethyl oleate.

Esterification process to synthesize isopropyl chloroacetate catalyzed by lanthanum dodecyl sulfate

Xu,Jiasheng; Zhang,Jie; Yin,Xiangyu; Yang,Dongjiang; Zhang,He; Qian,Jianhua; Liu,Lianli; Liu,Xiaoyang
Fonte: Brazilian Society of Chemical Engineering Publicador: Brazilian Society of Chemical Engineering
Tipo: Artigo de Revista Científica Formato: text/html
Publicado em 01/06/2011 EN
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Isopropyl chloroacetate has been synthesized by esterification of chloroacetic acid and isopropanol, using lanthanum dodecyl sulfate (LDDS) as the catalyst. Various factors that affected the esterification have been investigated, such as reaction time, different water-carrying agent and the amount of catalyst. Under the condition of 1.2/1 molar ratio of isopropanol to chloroacetic acid, 1.0% catalyst (molar percent of chloroacetic acid), 2.5 h reaction time, 5 mL cyclohexane as water-carrying agent and reflux temperature, the esterification conversion of isopropyl chloroacetate reaches 98.3%. The catalytic activity of LDDS is almost equal to that of a BrØnsted acid. LDDS, as one kind of water-tolerant Lewis acid, is an excellent catalyst compared to the traditional Lewis acid.

Otimização da esterificação da materia saponificavel do destilado de desodorização do oleo de soja; Optimization of esterification of the unsaponifiable matter of deodorization distillate of soybean oil

Nara Lucia Facioli
Fonte: Biblioteca Digital da Unicamp Publicador: Biblioteca Digital da Unicamp
Tipo: Tese de Doutorado Formato: application/pdf
Publicado em 08/03/2001 PT
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A esterificação (produção de ésteres metílicos e etílicos) da matéria saponificável do destilado de desodorização do óleo de soja (DDOS) é uma etapa importante para utilização deste resíduo, como matéria-prima, na produção de extratos ou concentrados de tocoferóis (Vit. E) e esteróis. Nesta pesquisa, foram otimizados três processos de esterificação da matéria saponificável do DDOS: 1- esterificação enzimática, utilizando álcool etílico comercial (96%) e Lipozyme'M(uma lipase imobilizada sn-1,3-específica do Mucor miehe/) como catalisador; 2- esterificação química ácida direta, usando álcool etílico anidro e ácido sulfúrico concentrado como catalisador e 3- saponificação/acidulaçãolesterificação com NaOH, H2SO4e álcool etílico. Para otimizar as condições de processo e se obterem as melhores taxas de conversão dos ácidos graxos (AG) em ésteres etílicos, preservando os tocoferóis, foi empregada a Metodologia de Superfície de Resposta, obtida através de um planejamento fatorial de 28 ordem. As condições ótimas de reação encontradas para a esterificação enzimática dos ácidos graxos livres (AGL) do DDOS foram: temperatura de 44 a 56°C; enzima de 12,6 a 17,4% e etanollAGL de 1...

Desenvolvimento de catalisadores alternativos para obtenção de ésteres alquílicos por transesterificação ou esterificação; Development of alternative catalysts for obtaining alkyl esters by transesterification or esterification

Melo, Ariana Maria Fernando de
Fonte: Universidade Federal de Alagoas; Brasil; Programa de Pós-Graduação em Engenharia Química; UFAL Publicador: Universidade Federal de Alagoas; Brasil; Programa de Pós-Graduação em Engenharia Química; UFAL
Tipo: Dissertação
POR
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374.05465%
Former works of our group have demonstrated the potential of catalytic systems based on titanium and zirconium in esterification of fatty acidy derived from soybean oil, in the presence of methanol. From these results, it arise the interest of evaluate the behavior of these systems in the presence of ethanol in the transesterification of soybean oil and in the esterification of fatty acid derived from this oil. In this context, this study aimed to investigate the catalytic activity of catalysts, exhibiting general formula M(n-butoxide)x (maltolate)4-x where M is titanium or zirconium, on the ethylic esterification and transesterification of soybean oil and soybean fatty acids, for obtaining biodiesel. Six catalysts were synthesized, two based on titanium and ford based on zirconium, in which the amount of the ligand maltolate (3-hydroxi-2-methyl-4-pironate), and n-butoxide. The formation of the complexes was confirmed by infrared spectroscopy. The catalytic activity of these catalysts was evaluated in the ethylic esterification via acid-base titulation, and ethylic transesterification via gas chromatography. The complexes M(n-butoxide)x (maltolate)4-x proved to be active in esterification, with conversions up to 81%, and in the transesterification yields up to 19%. When ethanol is used...

Genetic variability of carotenoid concentration and degree of esterification among tritordeum (xTritordeum Ascherson et Graebner) and durum wheat accessions

Atienza, Sergio G.; Ballesteros, Juan; Martín Muñoz, Antonio Pedro; Hornero-Méndez, Dámaso
Fonte: American Chemical Society Publicador: American Chemical Society
Tipo: Artículo Formato: 118 bytes; text/plain
ENG
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8 pages, 3 figures, 2 tables.-- PMID: 17439153 [PubMed].-- Printed version published May 16, 2007.; The higher carotenoid content (commonly referred as “yellow pigment content”) of tritordeum seeds as compared to wheat and the potential of this species as a donor of useful traits to wheat led us to investigate the detailed carotenoid composition of 53 accessions of hexaploid tritordeums originating from different stages of the tritordeum breeding program developed at IAS-CSIC. In addition, seven durum wheat accessions were also studied for comparison. Lutein was the unique carotenoid detected, either free or esterified with fatty acids. On average, tritordeum had 5.2 times more carotenoids than durum wheat, which suggests a high potential of this species to become a functional food. In addition, the most outstanding result of this work is the high esterification degree of lutein found in tritordeums as compared to durum wheat. This difference may indicate the differential esterification ability between tritordeum and durum wheat species. The implications of this high level of lutein esterification on both carotenoid accumulation and stability are discussed.; S.G.A. acknowledges financial support from the “Ramón y Cajal” program from the Spanish Ministry of Education (MEC). This research was financed by project AGL2005-01381 from MEC and FEDER.; Peer reviewed

Esterification of vertebrate-type steroids in the Eastern oyster (Crassostrea virginica)

Janer, Gemma; Mesia-Vela, Sonia; Porte Visa, Cinta; Kauffman, Frederick C.
Fonte: Elsevier Publicador: Elsevier
Tipo: Artículo Formato: 22195 bytes; application/pdf
ENG
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8 pages, 5 figures, 2 tables.-- PMID: 15013691 [PubMed].; Characteristics of acyl-coenzyme A (acyl-CoA):steroid acyltransferase from the digestive gland of the oyster Crassostrea virginica were determined by using estradiol (E2) and dehydroepiandrosterone (DHEA) as substrates. The apparent Km and Vmax values for esterification of E2 with the six fatty acid acyl-CoAs tested (C20:4, C18:2, C18:1, C16:1, C18:0, and C16:0) were in the range of 9–17 μM E2 and 35–74 pmol/min/mg protein, respectively. Kinetic parameters for esterification of DHEA (Km: 45–120 μM; Vmax: 30–182 pmol/min/mg protein) showed a lower affinity of the enzyme for this steroid. Formation of endogenous fatty acid esters of steroids by microsomes of digestive gland and gonads incubated in the presence of ATP and CoA was assessed, and at least seven E2 fatty acid esters and five DHEA fatty acid esters were observed. Some peaks eluted at the same retention times as palmitoleoyl-, linoleoyl-, oleoyl/palmitoyl-, and stearoyl-E2; and palmitoleoyl-, oleoyl/palmitoyl-, and stearoyl-DHEA. The same endogenous esters, although in different proportions, were produced by gonadal microsomes. The kinetic parameters for both E2 (Km: 10 μM; Vmax: 38 pmol/min/mg protein) and DHEA (Km: 61 μM; Vmax: 60 pmol/min/mg protein) were similar to those obtained in the digestive gland. Kinetic parameters obtained are similar to those observed in mammals; thus...

Esterification of vertebrate-like steroids in the eastern oyster (Crassostrea virginica)

Janer, Gemma; Mesia-Vela, Sonia; Wintermyer, Margy L.; Cooper, Keith R.; Kauffman, Frederick C.; Porte Visa, Cinta
Fonte: Elsevier Publicador: Elsevier
Tipo: Artículo Formato: 22195 bytes; application/pdf
ENG
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4 pages, 1 table.-- PMID: 15178069 [PubMed].-- Printed version published in issue Aug-Dec 2004.-- Issue title: "Twelfth International Symposium on Pollutant Responses in Marine Organisms" (Tampa Bay, FL, United States, May 9-13, 2003).; The esterification of two model vertebrate steroid hormones –estradiol (E2) and dehidroepiandrosterone (DHEA)– was studied in the oyster Crassostrea virginica. The activity of acyl-CoA:steroid acyltransferase was characterized in microsomal fractions isolated from oyster digestive glands. The apparent Km and Vmax values changed with the fatty acid acyl-CoA used (C20:4, C18:2, C18:1, C16:1, C18:0 or C16:0), and were in the range of 9–17 μM, and 35–74 pmol/min/mg protein for E2, and in the range of 45–120 μM, and 30–182 pmol/min/mg protein for DHEA. Kinetic parameters were also assessed in gonadal tissue. The enzyme saturated at similar concentrations, although conjugation rates were lower than in digestive gland. Preliminary data shows that tributyltin (TBT) in the low μM range (1–50) strongly inhibits E2 and DHEA esterification, the esterification of E2 being more sensitive to inhibition than that of DHEA. Overall, results indicate that apolar conjugation occurs in oysters, in both digestive gland and gonads...