Your browser doesn't support javascript.
loading
Mostrar: 20 | 50 | 100
Resultados 1 - 20 de 63
Filtrar
Mais filtros










Base de dados
Intervalo de ano de publicação
1.
Ann Oncol ; 21(1): 27-32, 2010 Jan.
Artigo em Inglês | MEDLINE | ID: mdl-19622593

RESUMO

OBJECTIVES: To develop a communication skills training (CST) module for health care professionals, particularly in the area of oncology, on how to conduct interviews using interpreters and to evaluate the module in terms of participant's self-efficacy and satisfaction. METHODS: Forty-seven multi-specialty health care providers from the New York Metropolitan Area attended a communication skills module at a Comprehensive Cancer Care Center about how to conduct clinical interviews utilizing interpreters. The development of this module was on the basis of current literature and followed the Comskil model previously utilized for other doctor-patient CSTs. Participants were given pre- and post-surveys to evaluate their own confidence as well as the helpfulness of the module. RESULTS: On the basis of a retrospective pre-post measure, participants reported an increase in their confidence about interviewing patients via translators. In addition, at least 80% of participants reported their satisfaction with the various components of the module by either agreeing or strongly agreeing with the different statements. CONCLUSIONS: We have developed a module that trains clinicians in effective collaboration with professional medical interpreters and shown its ability to increase the confidence of clinician's to work with limited English proficiency patients. Our approach intends to minimize not only the language barrier but also the cultural barriers that could potentially interfere with patients' care. PRACTICE IMPLICATIONS: This work has important practice implications in the oncology setting, where cultural sensitivity is paramount and empathic exchange with the patient optimizes their sense of being well supported by their health care team. We believe that this model is generalizable to many other medical settings where use needs to be made of a professional interpreter.


Assuntos
Barreiras de Comunicação , Educação Médica/métodos , Entrevistas como Assunto/métodos , Oncologia/educação , Tradução , Humanos , Relações Profissional-Paciente
2.
Euro Surveill ; 14(42)2009 Oct 22.
Artigo em Inglês | MEDLINE | ID: mdl-19883543

RESUMO

There are few structured data available to assess the risks associated with pandemic influenza A(H1N1)v infection according to ethnic groups. In countries of the Americas and the Pacific where these data are available, the attack rates are higher in indigenous populations, who also appear to be at approximately three to six-fold higher risk of developing severe disease and of dying. These observations may be associated with documented risk factors for severe disease and death associated with pandemic H1N1 influenza infection (especially the generally higher prevalence of diabetes, obesity, asthma, chronic obstructive pulmonary disease and pregnancy in indigenous populations). More speculative factors include those associated with the risk of infection (e.g. family size, crowding and poverty), differences in access to health services and, perhaps, genetic factors. Whatever the causes, this increased vulnerability of indigenous populations justify specific immediate actions in the control of the current pandemic including primary prevention (intensified hygiene promotion, chemoprophylaxis and vaccination) and secondary prevention (improved access to services and early treatment following symptoms onset) of severe pandemic H1N1 influenza infection.


Assuntos
Surtos de Doenças , Vírus da Influenza A Subtipo H1N1 , Influenza Humana/epidemiologia , Adolescente , Adulto , Brasil/epidemiologia , Humanos , Indígenas Norte-Americanos , Indígenas Sul-Americanos , Pessoa de Meia-Idade , Havaiano Nativo ou Outro Ilhéu do Pacífico , América do Norte/epidemiologia , Oceania/epidemiologia , Adulto Jovem
3.
Euro Surveill ; 14(26)2009 Jul 02.
Artigo em Inglês | MEDLINE | ID: mdl-19573511

RESUMO

Plague is circulating regularly in localised areas worldwide, causing sporadic cases outside Africa and remains endemic or causes limited outbreaks in some African countries. Furthermore, some notable outbreaks have been reported in Asia in the last 20 years. A limited outbreak with five cases has recently been notified by the health authorities of the Libyan Arab Jamahiriya.


Assuntos
Árabes/estatística & dados numéricos , Surtos de Doenças/estatística & dados numéricos , Peste/epidemiologia , Humanos , Incidência , Líbia/epidemiologia , Vigilância da População , Medição de Risco/métodos , Fatores de Risco
5.
J Anim Sci ; 85(11): 2972-81, 2007 Nov.
Artigo em Inglês | MEDLINE | ID: mdl-17565068

RESUMO

A study was conducted to investigate the biochemistry of digestion of field pea (Pisum sativum L.) albumins and globulins in the stomach and along the small intestine of weaned piglets with a particular emphasis on the respective roles of these compartments in pea protein digestion. Twenty-four piglets were weaned at 28 d of age. They were allocated to 2 diets (control and pea) and 3 slaughter times (3, 6, or 9 h after the last meal) in a 2 x3 factorial arrangement of treatments in a randomized complete block design. Pea flour provided 30% of total dietary protein in the pea diet. The diets were fed for 2 wk after weaning. After slaughter, gastrointestinal tract (GIT) compartments were weighed, digesta were collected, and pH was measured. Digesta from the stomach and cranial, middle, and caudal small intestine (SI) were extracted for soluble proteins and analyzed for specific pea proteins using SDS-PAGE, immunoblotting, and mass spectrometry. Tissue weight of the whole GIT (P = 0.015), cecum (P <0.001), and colon (P <0.001) was greater in the pea diet. Digesta pH in the stomach and caudal SI was lower (P = 0.02) in the pea diet than the control diet. In the stomach, vicilin, lectin, and pea albumin 2 were not digested, whereas legumin was only partly digested. Legumin and vicilin were totally digested in the SI in less than 3 h. A resistant peptide of 15 kDa located at the N-terminus of pea albumin 2 was transiently detected at 3 h. A protein band at 20 kDa was consistently identified as lectin. It was present in high intensity in intestinal digesta of pea-fed piglets at all times after the meal compared with those fed the control diet (P <0.001). Various proteins of, presumably, endogenous origin displayed differential digestion patterns between the control and the pea-fed piglets (P<0.05). In conclusion, differences in digestion between specific pea proteins were observed along the GIT of piglets. They could be partly explained by differences in protein digestion in the stomach.


Assuntos
Digestão , Mucosa Gástrica/metabolismo , Trato Gastrointestinal/metabolismo , Pisum sativum/metabolismo , Suínos/crescimento & desenvolvimento , Ração Animal , Fenômenos Fisiológicos da Nutrição Animal , Animais , Feminino , Trato Gastrointestinal/anatomia & histologia , Trato Gastrointestinal/crescimento & desenvolvimento , Concentração de Íons de Hidrogênio , Absorção Intestinal , Mucosa Intestinal/metabolismo , Intestino Grosso/anatomia & histologia , Intestino Grosso/crescimento & desenvolvimento , Intestino Grosso/metabolismo , Intestino Delgado/anatomia & histologia , Intestino Delgado/crescimento & desenvolvimento , Intestino Delgado/metabolismo , Masculino , Tamanho do Órgão , Lectinas de Plantas/metabolismo , Proteínas de Plantas/metabolismo , Distribuição Aleatória , Proteínas de Armazenamento de Sementes , Suínos/metabolismo , Desmame , Leguminas
6.
Colloids Surf B Biointerfaces ; 49(1): 40-8, 2006 Apr 15.
Artigo em Inglês | MEDLINE | ID: mdl-16581234

RESUMO

Two hydrolysis methods used to obtain rapeseed isolate derivates were compared: chemical hydrolysis performed under alkaline conditions and pepsic proteolysis performed under acidic conditions. The mean molecular weights obtained for the hydrolysates varied from 26 to 2.5 kDa, depending on the level of hydrolysis. Further characterisation showed that, at the same level of hydrolysis, the chemical hydrolysates differed by their charges and hydrophobicity from those derived from enzymatic digestion. Analysis of the foaming properties showed, for both cases, that a limited degree of hydrolysis, around 3%, was sufficient to optimise the foaming properties of the isolate despite the different physicochemical properties of the peptides generated. The study of foaming properties at basic, neutral and acidic pHs showed that the hydrolysate solutions yielded dense foams which drained slowly and which maintained a very stable volume under the three pH conditions tested.


Assuntos
Brassica rapa/química , Hidrolisados de Proteína/química , Fenômenos Químicos , Físico-Química , Concentração de Íons de Hidrogênio , Hidrólise , Interações Hidrofóbicas e Hidrofílicas , Peso Molecular , Peptídeos/química , Solubilidade , Soluções/química , Fatores de Tempo
7.
Artigo em Inglês | MEDLINE | ID: mdl-15722042

RESUMO

Rapeseed (Brassica napus L.) cruciferin (12S globulin), napin (2S albumin) and lipid transfer proteins (LTP) were purified at a multi-g scale. The procedure developed was simple, rather fast and resolutive; it permitted the recovery of these proteins with a good yield, such as 40% for cruciferin and 18% for napin. Nanofiltration eliminated the major phenolic compounds. The remaining protein fraction was fractionated by cation exchange chromatography (CEC) on a streamline SP-XL column in alkaline conditions. The unbound neutral cruciferin was polished by size exclusion chromatography. The alkaline napin isoforms and LTP, adsorbed on the beads, were eluted as a whole fraction and further separated by an other CEC step at acidic pH. Napins were polished by hydrophobic interaction chromatography (HIC). The fractions were characterized by reverse phase HPLC, electrophoresis, N-terminal sequencing and mass spectrometry. All the fractions contained less than 5% of impurities.


Assuntos
Brassica napus/química , Proteínas de Transporte/isolamento & purificação , Proteínas de Plantas/isolamento & purificação , Albuminas 2S de Plantas , Alérgenos , Sequência de Aminoácidos , Antígenos de Plantas , Cromatografia em Gel , Cromatografia por Troca Iônica/métodos , Eletroforese em Gel de Poliacrilamida , Isoformas de Proteínas/isolamento & purificação , Proteínas de Armazenamento de Sementes , Ultracentrifugação
8.
Biomacromolecules ; 5(4): 1596-601, 2004.
Artigo em Inglês | MEDLINE | ID: mdl-15244483

RESUMO

Wheat gluten films were prepared by thermo-pressing, and their mechanical properties were compared to those of cast films. The stress-strain relationship was established for films with various amounts of glycerol. Both relationships were quite different, revealing a different network organization. Thermo-pressed films presented higher stress values than cast films, but the effect of the glycerol amount was similar in both cases, an increase of the glycerol amount leading to a decrease of both films stress. The glycerol influence on the strain at break of thermo-pressed films was very limited, with strain values reaching a maximum around 200%. The role of disulfide bridges on themomoulded films mechanical properties was investigated, and it was shown that some rearrangements and a significative protein insolubilization occurred during the process. The effective flow porosity of the protein network for thermo-pressed films was estimated by water capillary rise measurements to about 7%. Scanning electron microscopy was used to obtain some information about the microstructure of both cast and thermo-pressed films.


Assuntos
Glutens/química , Glutens/ultraestrutura , Membranas Artificiais , Triticum/química , Dissulfetos/química , Tamanho da Partícula , Polímeros/química , Temperatura , Fatores de Tempo
9.
J Agric Food Chem ; 51(5): 1447-52, 2003 Feb 26.
Artigo em Inglês | MEDLINE | ID: mdl-12590496

RESUMO

The influence of a set of hydrophilic plasticizers varying in their chain length (ethyleneglycol and longer molecules) on the tensile strength and elongation at break of cast gluten films was studied. When considered on a molar basis (moles of plasticizer per mole of amino acid), the effect of the different plasticizers depended on their respective molecular weights for plasticizer/amino acid ratios in the range from 0.10 to 0.40. However, above a ratio of 0.40-0.50 mol/mol of amino acid, these differences were abolished and both stress and strain reached a plateau value, with all plasticizers studied. In fact, when a homologous series of molecules was considered, the ability for plasticizer to decrease stress and increase strain was closely related to the number of hydrogen bonds the molecule was able to share with the protein network. Ethyleneglycol's efficiency was, however, lower than expected from its hydrogen-bonding potential; a comparison with other diols demonstrated that this was due to the small size of this molecule. The particular effect of glycerol concentration on the films' mechanical properties suggested that other molecular features of the plasticizer, such as the number and position of hydroxide groups in the molecule, were involved in the plasticization mechanism.


Assuntos
Glutens/química , Plastificantes/química , Plastificantes/farmacologia , Triticum/química , Etilenoglicol/química , Etilenoglicol/farmacologia , Ligação de Hidrogênio , Peso Molecular , Relação Estrutura-Atividade , Resistência à Tração/efeitos dos fármacos
10.
Int J Pharm ; 242(1-2): 163-6, 2002 Aug 21.
Artigo em Inglês | MEDLINE | ID: mdl-12176239

RESUMO

Biopolymers represent an interesting alternative to synthetic polymers in order to be used as structured carriers for controlled release and encapsulation applications. In particular, the ability of these carriers to entrap both hydrophilic and hydrophobic drugs may be very promising for many applications. In addition, the absence of chemical compounds and organic solvents used to produce biopolymeric matrices could be very interesting for some industrial applications. Simple or complex coacervation methods involving proteins or protein and polysaccharide mixtures were used to create new matrices dedicated to controlled release applications. Controlled release experiments with model compounds were conducted in order to evaluate the performance of such matrices. An alternative and promising research field deals with particles obtained from hydrogel systems. Totally transparent solid matrices resulting from the dehydration of new protein gels were formed and swelling capacities of these matrices were studied.


Assuntos
Biopolímeros/química , Preparações de Ação Retardada , Portadores de Fármacos/química , Composição de Medicamentos/métodos , Coloides/química , Gliadina/administração & dosagem , Gliadina/química , Cinética , Lactoglobulinas/química , Tamanho da Partícula , Vitamina E/administração & dosagem , Vitamina E/química
11.
J Drug Target ; 10(8): 625-31, 2002 Dec.
Artigo em Inglês | MEDLINE | ID: mdl-12683667

RESUMO

Legumin is one of the main storage proteins in the pea seeds (Pisum sativum L.) and the molecules of this protein have the capacity of binding together to form nanoparticles after aggregation and chemical cross-linkage with glutaraldehyde. The aim of this work was to study the adaptive immune response of legumin nanoparticles in rats. Following intradermal immunisation with the native protein legumin and legumin nanoparticles of about 250 nm, the humoral and cell-mediated immune responses were analysed in rats. The humoral responses against legumin and legumin nanoparticles were examined by western blot and ELISA analysis. Both techniques clearly showed that sera from rats immunised with legumin strongly expressed antibodies against this protein. On the contrary, serum samples from rats inoculated with legumin nanoparticles did not contain detectable amounts of antibodies. These results may be explained by a reduction on the antigenic epitopes of the protein induced by the glutaraldehyde used during the cross-linking step. Concerning the cell-mediated response, neither legumin nor legumin nanoparticles stimulated an immunogenic response. This absence of response of spleen lymphocytes for legumin and legumin nanoparticles may be explained by a cytostatic effect of legumin which was corroborated by the evaluation of the middle phase of cell apoptose. In fact, both legumin and legumin nanoparticles are potent inductors of a cytostatic phenomenon and showed a significant increase of the chromatin condensation (p < 0.05) as compared with control.


Assuntos
Sistemas de Liberação de Medicamentos , Imunidade/efeitos dos fármacos , Proteínas de Plantas/administração & dosagem , Proteínas de Plantas/imunologia , Animais , Formação de Anticorpos/efeitos dos fármacos , Formação de Anticorpos/imunologia , Apoptose/efeitos dos fármacos , Western Blotting , Fenômenos Químicos , Físico-Química , Ensaio de Imunoadsorção Enzimática , Imunidade Celular/imunologia , Injeções Intradérmicas , Microesferas , Proteínas de Plantas/toxicidade , Ratos , Ratos Endogâmicos Lew , Leguminas
12.
J Agric Food Chem ; 49(2): 867-72, 2001 Feb.
Artigo em Inglês | MEDLINE | ID: mdl-11262042

RESUMO

The secondary structures of wheat gliadins (a major storage protein fraction from gluten) in film-forming solutions and their evolution during film formation were investigated by Fourier transform infrared spectroscopy. In the film-forming solution, wheat gliadins presented a mixture of different secondary structures, with an important contribution of beta-turns induced by proline residues. The presence of plasticizer did not have any influence on protein secondary structure in the film-forming solution. The evolution of protein conformation was followed during drying; the major feature of this evolution was a clear growing of the infrared band at 1622 cm(-1), characteristic of intermolecular hydrogen-bonded beta-sheets. This revealed the formation of protein aggregates during film drying. The influence of the drying temperature on film properties and gliadin secondary structures was also investigated. Higher drying temperatures induced an increase of both the tensile strength of the films and the amount of beta-sheets aggregates. Although the appearance of heat-induced disulfide bridge cross-links has already been described, there is clear evidence that hydrogen-bonded beta-sheets aggregates are also induced by thermal treatment. It was not possible, however, to determine whether there is a direct relationship between the occurrence of these aggregates and the increase of the tensile strength of the films.


Assuntos
Gliadina/química , Triticum , Plastificantes , Conformação Proteica , Estrutura Secundária de Proteína , Espectroscopia de Infravermelho com Transformada de Fourier/métodos
13.
Nahrung ; 44(5): 309-17, 2000 Oct.
Artigo em Inglês | MEDLINE | ID: mdl-11075371

RESUMO

The foaming properties of bovine beta-lactoglobulin (BLG), BNPS-skatole (2-(2'-nitrophenylsulfenyl)-3-methyl-3'-bromoindolenine) (BNPS), trypsin (T) and pepsin in 25, 30 and 40% ethanol (P25, P30, P40) hydrolysates were investigated in the 0.2 to 1 mg/ml range. Foaming capacity and foam stability were assessed in terms of drained liquid volume and foam volume. Foam texture was analyzed from video images obtained during foam decay. The foaming capacity of BNPS, P30 and P40 was similar to that of BLG and greater than that of T or P25. All hydrolysates except BNPS were less stable than BLG at all concentrations tested. This result was insured by texture analysis. Principal component analysis confirmed the distribution of the samples into three groups based on their increasing stability: (i): P25, (ii): P30 and P40, and (iii): BLG and BNPS. Tryptic hydrolysate had the poorest foaming properties. The results are considered in relation to the molecular characteristics of the peptides, particularly their size and hydrophobicity.


Assuntos
Lactoglobulinas/química , Peptídeo Hidrolases/química , Hidrolisados de Proteína/química , Animais , Bovinos , Cromatografia Líquida de Alta Pressão , Hidrólise , Fatores de Tempo
14.
J Agric Food Chem ; 48(11): 5444-9, 2000 Nov.
Artigo em Inglês | MEDLINE | ID: mdl-11087499

RESUMO

Films were prepared at neutral pH from deamidated gluten by casting with or without enzymatic treatment by transglutaminase in the presence of various concentrations of diamines added to the film-forming solution. Variation in the glycerol/deamidated gluten ratio from 0.2 to 0.5 had a major effect on the film mechanical properties, which is characteristic of a plasticizing effect. A ratio of 0.35, producing a tensile strength of 1.14 +/- 0.12 MPa and an elongation at break of 376 +/- 62%, was chosen for most of the enzymatic modifications. The action of transglutaminase with or without the addition of external diamines induced a simultaneous increase in tensile strength and elongation at break of the films but tended to decrease the contact angle between the film surface and a water droplet. The presence of diamines in the film solution affected the elongation at break more than the tensile strength of the films. These diamines, able to react at their two extremities, probably acted as spacers between gluten proteins. The decrease in solubility was related to the formation of high molecular weight polymers in the film. The film properties were unaffected by the type of diamine added as secondary substrate in the transglutaminase reaction.


Assuntos
Diaminas/química , Glutens/química , Amidas , Cadaverina/química , Reagentes de Ligações Cruzadas , Glutens/metabolismo , Glicerol/análise , Concentração de Íons de Hidrogênio , Putrescina/química , Solubilidade
15.
Nahrung ; 44(2): 89-95, 2000 Apr.
Artigo em Inglês | MEDLINE | ID: mdl-10795574

RESUMO

Bovine beta-Lactoglobulin (BLG) was cleaved by BNPS-skatole (2-(2'-nitrophenylsulfenyl)-3-methyl-3'-bromoindolenine), trypsin, or pepsin in 40% ethanol before emulsification with hexadecane in order to characterize the peptides active at the interfaces. The total digests and the different phases obtained after emulsification were analyzed by RP-HPLC to separate the peptides according to their gradual order on a hydrophilicity-to-hydrophobicity scale. In each case, hydrophobic peptides were recovered in the creamed phase and characterized by mass spectrometry and sequencing. After tryptic hydrolysis, short peptides were identified at the interfacial layer as fragments S21-L32, V41-L57, V41-K60, and W61-K70 linked to L149-I162 by a C66-C160 bond. It indicates that the hydrophilic/hydrophobic distribution of the amino acids in the sequence of the fragments is more relevant to adsorption than the length of the peptide. BNPS-skatole and peptic hydrolysis produced larger hydrophobic peptides which were also recovered in the creamed phase of the emulsion and characterized.


Assuntos
Lactoglobulinas/química , Peptídeos/análise , Hidrolisados de Proteína/análise , Sequência de Aminoácidos , Animais , Bovinos , Cromatografia Líquida de Alta Pressão , Emulsões , Hidrólise , Dados de Sequência Molecular , Pepsina A , Escatol/análogos & derivados , Tripsina
16.
J Agric Food Chem ; 48(4): 1064-9, 2000 Apr.
Artigo em Inglês | MEDLINE | ID: mdl-10775350

RESUMO

The conditions for protein film preparation from an alkaline dispersion of a pea protein isolate were investigated in the presence of polyols as plasticizers. Mechanical and barrier properties of resulting films were studied as a function of protein dispersion conditions, protein and plasticizer concentrations and ratios, chain length of the plasticizer, and pH and composition of the alkaline medium. Neither the mode of protein hydration nor the pea isolate origin had a significant effect on the mechanical properties of pea protein films. However, increasing the plasticizer chain length induced slightly higher surface hydrophobicity but poor mechanical properties. Addition of monoglycerides to film-forming solution allowed a significant improvement of the films during aging. Both tensile strength and surface hydrophobicity increased when ammonium hydroxide was used as protein dispersing agent instead of sodium hydroxide.


Assuntos
Conservação de Alimentos/métodos , Pisum sativum/química , Proteínas de Plantas/química , Proteínas de Plantas/isolamento & purificação , Plastificantes
17.
J Agric Food Chem ; 47(12): 5218-26, 1999 Dec.
Artigo em Inglês | MEDLINE | ID: mdl-10606599

RESUMO

Lysyl residues of rapeseed napin (2S) and cruciferin (12S) were acylated and sulfamidated by means of anhydrides and sulfonyl chlorides, respectively. The secondary and tertiary structures as well as the surface hydrophobicity of the modified proteins were studied using circular dichroism, intrinsic fluorescence, and binding of anilinonaphthalenesulfonic acid. The results showed clearly that grafting of hydrophobic chains induced different structural modifications and surface hydrophobicities on the monomeric (2S) and on the hexameric (12S) proteins. Thus, the original structure of the 2S modified protein seemed to be preserved. Therefore, the surface hydrophobicity increased proportionally with the number of groups grafted. Conversely, after modification, 12S was shown to be expanded. As a result, hydrophobic regions were exposed, leading to a much greater hydrophobization of the protein surface. Acylation and sulfamidation appeared, therefore, to be good methods to hydrophobize efficiently the surface of the two proteins and thus might probably induce new functional properties.


Assuntos
Brassica , Sondas Moleculares/síntese química , Proteínas de Plantas/química , Albuminas 2S de Plantas , Acilação , Alérgenos , Antígenos de Plantas , Dicroísmo Circular , Manipulação de Alimentos , Humanos , Proteínas de Armazenamento de Sementes , Relação Estrutura-Atividade , Propriedades de Superfície
18.
J Protein Chem ; 18(3): 325-36, 1999 Apr.
Artigo em Inglês | MEDLINE | ID: mdl-10395451

RESUMO

Bovine serum albumin was chosen as a model protein to study the effect of the functionalization of the epsilon-NH2 of lysine residues with different carbon chains on the physical properties of proteins. Thus, BSA has been acylated and sulfonylated by means of anhydrides and sulfonyl chlorides, respectively. The secondary structures of modified BSA, studied by far-UV CD, showed very slight changes except after sulfamidation. However, near-UV CD and intrinsic fluorescence spectra revealed important conformational perturbations for proteins bearing long carbon chains. Furthermore, the binding of an apolar probe (ANS) to BSA revealed an improvement of surface hydrophobicity after modification. Meanwhile, Scatchard plot results indicate that only 20% of the hexanoyl carbon chains lie at the surface of the proteins. Solvent conditions should influence the exposure of these chains and consequently the surface hydrophobicity of proteins.


Assuntos
Soroalbumina Bovina/química , Acilação , Dicroísmo Circular , Espectrometria de Massas , Modelos Químicos , Conformação Proteica , Engenharia de Proteínas , Espectrometria de Fluorescência , Propriedades de Superfície , Água/química
19.
Biochem J ; 340 ( Pt 1): 329-36, 1999 May 15.
Artigo em Inglês | MEDLINE | ID: mdl-10229689

RESUMO

The formation of a reversible adsorption complex between a dimer of N-acetyl-L-tyrosine [di-(N-acetyl-L-tyrosine), (NAT)2] and horseradish peroxidase (HRP) compound II (CII) was demonstrated using a kinetic approach. A specific KIIm value (0.58 mM) was deduced for this step from stopped-flow measurements. The dimerization of the dipeptide Gly-Tyr was analysed at the steady state and compared with (NAT)2 dimerization [(NAT)2-->(NAT)4]. A saturation of the enzyme was observed for both substrates within their range of solubility. In each case the rate of dimerization reflected the rate-limiting step of compound II reduction to the native HRP (E) (kappcat/Kappm approximately kII-->E). The kappcat values for (Gly-Tyr)2 and (NAT)4 formation were 254 s-1 and 3.6 s-1 respectively. The KappM value of Gly-Tyr was 24 mM. It was observed that the value (0.7 mM) for (NAT)2 was close both to its specific KIIm value for the second step of reduction (CII-->E) and to its thermodynamic dissociation constant (Kd=0.7 mM) with the resting form of the enzyme. As (NAT)2 was a tighter ligand but a poorer substrate than Gly-Tyr, a steady-state kinetic study was performed in the presence of both substrates. A kinetic model which includes an enzyme-substrate adsorption prior to each of the two steps of reduction was derived. This one agreed reasonably well with the experimental data.


Assuntos
Peroxidase do Rábano Silvestre/metabolismo , Tirosina/análogos & derivados , Adsorção , Catálise , Dimerização , Relação Dose-Resposta a Droga , Elétrons , Glicina/metabolismo , Cinética , Ligantes , Modelos Químicos , Oxirredução , Polímeros/metabolismo , Solubilidade , Termodinâmica , Titulometria , Tirosina/metabolismo
20.
Biotechnol Bioeng ; 63(4): 449-58, 1999 May 20.
Artigo em Inglês | MEDLINE | ID: mdl-10099625

RESUMO

"Enzyme-assisted" oxidative polymerization of wheat gliadins was performed in an attempt to obtain new protein-based networks. Two plant peroxidases (soybean and horseradish) were used to induce the dimerization of tyrosine residues. The results show that tyrosines are poorly modified by these enzymes in an aqueous medium (dityrosine corresponded to 2% of the total amount of tyrosine). Two approaches were tested to overcome problems relating to accessibility to the target tyrosines: First, the efficiency of protein crosslinking via tyrosine-tyrosine aromatic ring condensation was enhanced in water when the proteins were oxidized by a fungus peroxidase (manganese-dependent peroxidase from Phanerochaete chrysosporium), which acts according to an indirect catalysis mechanism (up to 12% of the total amount of tyrosine is recovered under a dimeric form). Second, when the gliadins were dispersed in a water/dioxane (3/1) mixed solvent system, the tyrosines were more accessible on the protein surface, and similar yields were obtained with both types of peroxidase. The two types of catalysis (contact and indirect) are considered from the standpoint of the accessibility of the target residues. Enzymatic oxidations were also performed on synthetic peptides mimicking the repeatitive domains of gliadins. The results show that exposure of tyrosine to the solvent may not be sufficient to induce dityrosine formation. The mechanical properties of some films obtained from peroxidase-treated gliadins were investigated to correlate protein crosslinking with a potential application. One effect of the enzymatic treatment was to increase the tensile strength of the films. Copyright 1999 John Wiley & Sons, Inc.

SELEÇÃO DE REFERÊNCIAS
DETALHE DA PESQUISA
...