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1.
Med J Malaysia ; 73(1): 16-24, 2018 02.
Artigo em Inglês | MEDLINE | ID: mdl-29531198

RESUMO

BACKGROUND: The Diabetes Mellitus in the Offspring Questionnaire (DMOQ) assesses the perceptions of Type 2 diabetes mellitus (T2DM) patients on the risk of their offspring developing T2DM and the possibility of intervention to reduce this risk. It has 34 items framed within seven domains. This study aimed to adapt, translate and validate the DMOQ from English into the Malay language. METHODS: This was a cross-sectional validation study among 159 T2DM patients attending a public primary care clinic in Selangor. The DMOQ English version underwent adaptation, translation, face validation and field testing to produce the Malay version. Psychometric analysis was performed using Exploratory Factor Analysis, internal consistency and testretest reliability. RESULTS: The DMOQ domains were conceptually equivalent between English and Malay language. A total of 13 items and two domains were removed during the validation process (three items during the content validation, three items due to poor factor loadings, five items as they loaded onto two domains which were not interpretable, one item as it did not fit conceptually into the factor it loaded onto and one openended question as it did not fit into the retained domains). Therefore, the final DMOQ Malay version consisted of 21- items within five domains. The Cronbach alpha was 0.714 and the intraclass-correlation coefficient was 0.868. CONCLUSION: The DMOQ Malay version is a valid and reliable tool which is consistent over time. It can be used to examine the perception of T2DM patients towards the risk of their offspring developing diabetes and possibility of intervention in Malay-speaking patients.


Assuntos
Diabetes Mellitus Tipo 2/psicologia , Pais/psicologia , Filho de Pais com Deficiência/estatística & dados numéricos , Estudos Transversais , Diabetes Mellitus Tipo 2/epidemiologia , Análise Fatorial , Feminino , Humanos , Malásia , Masculino , Pessoa de Meia-Idade , Psicometria , Reprodutibilidade dos Testes , Fatores de Risco , Inquéritos e Questionários , Tradução
2.
Eur J Vasc Endovasc Surg ; 51(5): 707-17, 2016 05.
Artigo em Inglês | MEDLINE | ID: mdl-27067191

RESUMO

BACKGROUND: Peripheral arterial bypass is an effective procedure for the management of patients with critical limb ischaemia. However, it is commonly associated with high rates of graft occlusion and subsequent limb loss. This is particularly apparent when the distal anastomosis is to the below-knee arterial segment. A number of studies have suggested that an arteriovenous fistula (AVF) sited at the distal anastomosis may reduce afterload, improve graft patency, and boost subsequent limb salvage. The aim of this study was to assess the effects of adjuvant AVF on the outcomes of peripheral arterial bypass. METHODS: The following databases were searched up to May 2015: Medline through Pubmed; the Cochrane Library; EMBASE; and reference lists of articles. STUDY ELIGIBILITY: All randomised controlled and observational studies that assessed the role of AVF as an adjunct to peripheral arterial bypass were included. Studies were required to include at least one pre-defined outcome. Data were extracted and assessed by two reviewers with any disagreements adjudicated on by the senior author. Pooled risk ratios were calculated using a random effects model. Additional subgroup analyses were performed. RESULTS: Two randomised controlled trials and seven retrospective cohort studies comprising 966 participants were included. Pooled standardized data showed no difference in primary graft patency (pooled RR = 1.25, 95% CI 0.73-2.16), secondary patency (pooled RR = 1.16, 95% CI 0.82-1.66), or limb salvage at 12-months (pooled RR = 1.13, 95% CI 0.80-1.60) for the peripheral bypass with AVF group compared with peripheral bypass alone. Subgroup analysis indicated a reduction in reintervention rates associated with AVF when performed in conjunction with a synthetic graft (pooled RR = 0.55, 95% CI 0.30-0.98). CONCLUSION: Although adjuvant AVF is not associated with additional operative complication there is little evidence to support its use. The evidence assessing its merits is weakened by small, retrospective studies with heterogeneous cohorts.


Assuntos
Derivação Arteriovenosa Cirúrgica/métodos , Doenças Vasculares Periféricas/cirurgia , Enxerto Vascular/métodos , Humanos , Resultado do Tratamento
3.
BMJ ; 342: d715, 2011 Feb 15.
Artigo em Inglês | MEDLINE | ID: mdl-21324992

RESUMO

OBJECTIVE: To test the effectiveness of peer support for patients with type 2 diabetes. DESIGN: Cluster randomised controlled. SETTING: 20 general practices in the east of the Republic of Ireland. PARTICIPANTS: 395 patients (192 in intervention group, 203 in control group) and 29 peer supporters with type 2 diabetes. INTERVENTION: All practices introduced a standardised diabetes care system. The peer support intervention ran over a two year period and contained four elements: the recruitment and training of peer supporters, nine group meetings led by peer supporters in participant's own general practice, and a retention plan for the peer supporters. MAIN OUTCOME MEASURES: HbA(1c); cholesterol concentration; systolic blood pressure; and wellbeing score. RESULTS: There was no difference between intervention and control patients at baseline. All practices and 85% (337) of patients were followed up. At two year follow-up, there were no significant differences in HbA(1c) (mean difference -0.08%, 95% confidence interval -0.35% to 0.18%), systolic blood pressure (-3.9 mm Hg, -8.9 to 1.1 mm Hg), total cholesterol concentration (-0.03 mmol/L, -0.28 to 0.22 mmol/L), or wellbeing scores (-0.7, -2.3 to 0.8). While there was a trend towards decreases in the proportion of patients with poorly controlled risk factors at follow-up, particularly for systolic blood pressure (52% (87/166) >130 mm Hg in intervention v 61% (103/169) >130 mm Hg in control), these changes were not significant. The process evaluation indicated that the intervention was generally delivered as intended, though 18% (35) of patients in the intervention group never attended any group meetings. CONCLUSIONS: A group based peer support intervention is feasible in general practice settings, but the intervention was not effective when targeted at all patients with type 2 diabetes. While there was a trend towards improvements of clinical outcomes, the results do not support the widespread adoption of peer support. Trial registration Current Controlled Trials ISRCTN42541690.


Assuntos
Grupo Associado , Apoio Social , Idoso , Pressão Sanguínea/fisiologia , Colesterol/metabolismo , Análise por Conglomerados , Diabetes Mellitus Tipo 2/sangue , Diabetes Mellitus Tipo 2/fisiopatologia , Diabetes Mellitus Tipo 2/terapia , Feminino , Hemoglobinas Glicadas/metabolismo , Humanos , Masculino , Pessoa de Meia-Idade , Fatores de Risco , Grupos de Autoajuda/organização & administração , Terapêutica
4.
Ir J Med Sci ; 180(2): 475-8, 2011 Jun.
Artigo em Inglês | MEDLINE | ID: mdl-21290198

RESUMO

INTRODUCTION: There have been reports of thalidomide-affected people suffering a deterioration in their disability over time [1, 2]. This study assessed changes in disabilities among thalidomide-affected people in the Irish population. METHODS: A questionnaire, assessing musculo-skeletal health, quality-of-life, general health and illness intrusiveness was sent to 26 people affected by thalidomide in the Republic of Ireland. RESULTS: Seventeen (65%) responded. Six (35%) respondents were not working as a result of their disability. Eleven (65%) reported a worsening of their disability over time, with nine of them reporting the deterioration as moderate to severe. The impact of this decline was measured by respondents in terms of ability to perform daily tasks, emotional health and finances (due to extra costs related to clothing, transport, housing alterations and heating). CONCLUSION: There is a need to continually review the physical, psychological and social needs of thalidomide survivors in order to ensure optimum care is made available.


Assuntos
Pessoas com Deficiência/psicologia , Nível de Saúde , Doenças Musculoesqueléticas/congênito , Efeitos Tardios da Exposição Pré-Natal , Qualidade de Vida/psicologia , Talidomida/efeitos adversos , Atividades Cotidianas , Adulto , Braço/anormalidades , Feminino , Humanos , Perna (Membro)/anormalidades , Masculino , Pessoa de Meia-Idade , Limitação da Mobilidade , Doenças Musculoesqueléticas/psicologia , Dor , Gravidez
5.
Ir J Med Sci ; 176(3): 221-4, 2007 Sep.
Artigo em Inglês | MEDLINE | ID: mdl-17659430

RESUMO

BACKGROUND: The numbers of removals of patients from General Practitioner lists in Ireland is increasing and is a cause for some concern. AIMS: To examine the views of both general practitioners and patients toward removals of patients from general practitioner lists. METHODS: Questionnaire survey to general practitioners in North Inner City Dublin who had removed patients from their list over a 1-year period (n = 45) and to the patients they had removed (n = 86). Follow up semi structured interviews were carried out with five general practitioners and ten patients. RESULTS: For doctors, the decision to remove a problematic patient from their list is generally a positive experience, providing relief and being associated with certainty in both the decision and the process. For the patient, being removed from a GP's list is a negative experience, stressful and confusing. CONCLUSIONS: There is a need for the development of a clear responsive, transparent and supportive system for removing patients from a GP list.


Assuntos
Atitude do Pessoal de Saúde , Medicina de Família e Comunidade/estatística & dados numéricos , Satisfação do Paciente/estatística & dados numéricos , Pacientes/psicologia , Relações Médico-Paciente , Recusa em Tratar/estatística & dados numéricos , Adulto , Feminino , Humanos , Irlanda , Masculino
6.
Ir Med J ; 99(8): 236-8, 2006 Sep.
Artigo em Inglês | MEDLINE | ID: mdl-17120606

RESUMO

Diabetes management in Irish Primary Care is in the early stages of development. This study used a Delphi technique with a panel of experts working in diabetes in primary care in order to reach a consensus on its future development. There was strong agreement on the need for multidisciplinary professional advocacy to improve services for people with diabetes. The panel indicated a preference for the development of shared models of care and emphasised the importance of research, audit and professional education. The results of this study can be used by health planners to develop services in a way that reflects the experience and opinion of those working as experts in the field of primary care diabetes.


Assuntos
Diabetes Mellitus/terapia , Atenção Primária à Saúde , Consenso , Técnica Delphi , Humanos , Irlanda
7.
Ir J Med Sci ; 175(4): 42-7, 2006.
Artigo em Inglês | MEDLINE | ID: mdl-17312828

RESUMO

BACKGROUND: For people with type 2 diabetes to enjoy improved longevity and quality of life, care needs to be organised in a systematic way. AIM: To test if processes and intermediate outcomes for patients with type 2 diabetes changed with the move to structured care in general practice shared with secondary care. METHODS: An audit of process and intermediate outcomes for patients with type 2 diabetes before and after the change to structured care in 10 Dublin general practices shared with secondary care four years on. RESULTS: Structured diabetes care in general practice has led to more dedicated clinics improved processes of care and increased access to multidisciplinary expertise. Improvement in blood pressure control, the use of aspirin and the use of lipid lowering agents indicate a significant decrease in absolute risk of vascular events for this population. CONCLUSIONS: Structured care in general practice improves intermediate outcomes for people with type 2 diabetes. Further improvements need to be made to reach international targets.


Assuntos
Diabetes Mellitus Tipo 2/epidemiologia , Diabetes Mellitus Tipo 2/terapia , Medicina de Família e Comunidade , Atenção Primária à Saúde , Idoso , Feminino , Hemoglobinas Glicadas , Humanos , Irlanda , Masculino , Auditoria Médica , Avaliação de Processos e Resultados em Cuidados de Saúde , Abandono do Hábito de Fumar
8.
Diabet Med ; 21(11): 1221-8, 2004 Nov.
Artigo em Inglês | MEDLINE | ID: mdl-15498089

RESUMO

AIMS: To evaluate whether diabetes care in a district population can be sustained over time and intensive management of multiple risk factors can be achieved against a background of rising prevalence of known diabetes and shift of responsibility towards primary care. METHODS: Assessment of process and outcome measures achieved by a comprehensive diabetes service. Routine data were collected from patients registered with diabetes in a district population by repeated cross-sectional survey in 1991 (n = 2284 patients) and 2001 (n = 5809 patients). RESULTS: Between 1991 and 2001 the recording of body mass index (76.8 vs. 71.3%, P = 0.01) and HbA(1c) measurement (92.2 vs. 86.4%, P < 0.001) decreased, whereas recording of smoking status (72.4 vs. 82%, P < 0.001), cholesterol level (54.7 vs. 82.5%, P < 0.001) and eye screening result (86.1 vs. 91.3%, P < 0.001) improved. Surviving patients with Type 2 diabetes had significant improvements in systolic blood pressure, diastolic blood pressure and cholesterol, significant deterioration in HbA(1c) and creatinine, and no change in body mass index. Changes in blood pressure and HbA(1c) over time were similar to those reported in the UKPDS. CONCLUSIONS: The delivery of processes and outcomes of care to a district population can be sustained at a high level over a 10-year period within a comprehensive diabetes service. We would suggest that a multifaceted complex intervention is required to achieve these results.


Assuntos
Atenção à Saúde/normas , Diabetes Mellitus/terapia , Atenção Primária à Saúde/normas , Qualidade da Assistência à Saúde , Adulto , Idoso , Pressão Sanguínea , Colesterol/sangue , Estudos Transversais , Diabetes Mellitus/sangue , Diabetes Mellitus/epidemiologia , Diabetes Mellitus Tipo 2/sangue , Diabetes Mellitus Tipo 2/epidemiologia , Diabetes Mellitus Tipo 2/terapia , Inglaterra/epidemiologia , Feminino , Hemoglobinas Glicadas/metabolismo , Pesquisa sobre Serviços de Saúde , Humanos , Masculino , Pessoa de Meia-Idade , Avaliação de Processos e Resultados em Cuidados de Saúde , Prevalência
9.
Diabet Med ; 21(6): 640-3, 2004 Jun.
Artigo em Inglês | MEDLINE | ID: mdl-15154955

RESUMO

AIMS: Alongside a rising prevalence of known diabetes, patterns of care for diabetes have been changing in the United Kingdom. The aim of this study is to describe the changes in the prevalence of known diabetes and shift in site of care of patients in a single health district over a 10-year period. METHODS: Repeat cross-sectional study over 10 years of patients with diabetes resident in North Tyneside district. RESULTS: The crude prevalence of known diabetes in North Tyneside rose from 1.1 to 3.0% between 1991 and 2001. The proportion of patients receiving their diabetes care wholly in primary care rose significantly from 608/2236 (27%) in 1991 to 3995/5809 (69%) in 2001 (chi(2) = 968, 1 d.f., P < 0.001). The number of patients attending secondary care also rose by 14% over this period of time from 1508 to 1712 patients. CONCLUSIONS: Most of the extra workload of the rising prevalence of diabetes has been met in primary care. However, hospital care has not seen a drop in workload. This has important implications for health care planning, as an increase in resources will be required within both primary and secondary care to meet the needs of the diabetic population.


Assuntos
Diabetes Mellitus/epidemiologia , Atenção Primária à Saúde , Estudos Transversais , Inglaterra/epidemiologia , Hospitais , Humanos , Aceitação pelo Paciente de Cuidados de Saúde , Prevalência
10.
Diabet Med ; 20(2): 155-8, 2003 Feb.
Artigo em Inglês | MEDLINE | ID: mdl-12581268

RESUMO

AIMS: Screening for Type 2 diabetes does not meet all the criteria for screening, yet is increasingly proposed. The views of health care professionals towards screening for Type 2 diabetes are not known. We set out to explore the attitudes and beliefs held by general practitioners (GPs) and practice nurses towards screening for Type 2 diabetes. METHODS: Semistructured interviews with 10 GPs and nine practice nurses in eight general practices in North-east England. Data collection and analysis proceeded in an iterative manner in accordance with grounded theory. RESULTS: Practitioners who perceive themselves to be most aware of the evidence base surrounding screening for Type 2 diabetes are least likely to support its introduction. Those who support screening for Type 2 diabetes hold a 'common sense' viewpoint that earlier detection must be better and believe that patients demand and respect early diagnosis. Practitioners acknowledge a lack of knowledge and skills to promote lifestyle changes. This deficiency is combined with workload issues, contributing towards a medicalized view of diabetes screening. CONCLUSIONS: The belief that screening for Type 2 diabetes is worthwhile is based not on evidence for the effectiveness of screening, but rather on a complex interaction of factors including perceptions of patient desires and an interplay of previous experience and evidence from other sources. Increased resources would be most likely to promote screening in primary care.


Assuntos
Atitude do Pessoal de Saúde , Diabetes Mellitus Tipo 2/diagnóstico , Programas de Rastreamento , Profissionais de Enfermagem/psicologia , Médicos de Família/psicologia , Diabetes Mellitus Tipo 2/psicologia , Inglaterra , Humanos
11.
Br J Gen Pract ; 51(466): 381-3, 2001 May.
Artigo em Inglês | MEDLINE | ID: mdl-11360703

RESUMO

There exists wide variation in practice regarding the use of chaperones for physical examination of the patient in primary care. Guidelines agree that a chaperone should be offered or used whenever a patient is undergoing an intimate examination. This paper aims to gauge patient views on the use of chaperones in primary care. Focus groups were used to identify themes surrounding the use of chaperones in primary care. Questionnaires were then mailed to 404 women and 400 men aged 16 years to 65 years identified from the lists of three research practices in the Northern and Yorkshire Region. The most important factor for the patient in an intimate examination is the attitude of the doctor; the patient views the offer of a chaperone as a sign of respect by the doctor. The development of shared decision-making within a consultation involving an intimate examination should be seen as more important than a rigid approach towards using a chaperone.


Assuntos
Atitude , Satisfação do Paciente , Exame Físico/psicologia , Adolescente , Adulto , Idoso , Feminino , Grupos Focais , Humanos , Masculino , Pessoa de Meia-Idade , Serviço de Acompanhamento de Pacientes , Exame Físico/métodos , Relações Médico-Paciente , Inquéritos e Questionários
12.
Biochem J ; 352 Pt 1: 117-24, 2000 Nov 15.
Artigo em Inglês | MEDLINE | ID: mdl-11062064

RESUMO

The cytochrome b(5) tail is a 43-residue membrane-embedded domain that is responsible for anchoring the catalytic domain of cytochrome b(5) to the endoplasmic reticulum membrane. Different models for the structure of the membrane domain of cytochrome b(5) have been proposed, including a helical hairpin and a single transmembrane helix. In the present study, CD spectroscopy was used to investigate the conformation of the tail in different environments, and as a function of temperature, with the goal of understanding the nature of the membrane-bound conformation. Whereas residue property profiling indicates that bending of a helix in the middle of the peptide might be possible, the experimental results in small unilamellar vesicles and lysophosphatidylcholine micelles are more consistent with a single transmembrane helix. Furthermore, although there is evidence for some refolding of the polypeptide with temperature, this is not consistent with a hairpin-to-transmembrane transition. Rather, it appears to represent an increase in helical content in fluid lipid environments, perhaps involving residues at the ends of the transmembrane segment.


Assuntos
Membrana Celular/metabolismo , Citocromos b5/química , Sequência de Aminoácidos , Animais , Domínio Catalítico , Bovinos , Membrana Celular/química , Dicroísmo Circular , Eletroforese em Gel de Poliacrilamida , Modelos Biológicos , Dados de Sequência Molecular , Fosfolipídeos/metabolismo , Conformação Proteica , Estrutura Secundária de Proteína , Estrutura Terciária de Proteína , Homologia de Sequência de Aminoácidos , Temperatura
13.
Br J Gen Pract ; 50(456): 573-6, 2000 Jul.
Artigo em Inglês | MEDLINE | ID: mdl-10954942

RESUMO

There is, as yet, no strong culture of research in primary care and much of the existing research is conceived and undertaken by people outside primary care. The poor implementation of research findings may, in part, be owing to the fact that those delivering the service are not involved in asking or answering questions that are relevant to their practice. This paper reports how three practices constructed a research agenda based on the unanswered questions of their primary care teams. The research questions prioritised by the teams tended towards patient behaviour and service organisation rather than clinical issues. This contrasts with national research priorities. The process has contributed towards the development of a culture of enquiry among team members. Other primary care teams may benefit from a similar approach. National research priority setting in primary care should take more account of the unanswered questions of primary care teams.


Assuntos
Atenção Primária à Saúde , Pesquisa/organização & administração , Medicina de Família e Comunidade/organização & administração , Implementação de Plano de Saúde , Humanos , Medicina Estatal , Reino Unido
14.
FEBS Lett ; 476(3): 287-95, 2000 Jul 07.
Artigo em Inglês | MEDLINE | ID: mdl-10913630

RESUMO

The nuclear magnetic resonance solution structure of alpha-conotoxin SI has been determined at pH 4.2. The 36 lowest energy structures show that alpha-conotoxin SI exists in a single major solution conformation and is stabilized by six hydrogen bonds. Comparisons are made between the SI solution structure and the solution and crystal structures of alpha-conotoxin GI. Surprisingly, a high degree of similarity between the backbone conformations of the GI crystal and the SI solution structures is seen in the region of lowest sequence homology, namely residues Gly-8 to Ser-12. This similarity is more surprising when considering that in SI a proline replaces the Arg-9 found in GI. The correspondence in conformation in this region provides the definitive evidence that it is the loss of the arginine basic charge at residue 9 which determines the differences in toxicity between GI and SI, rather than any changes in conformation induced by the cyclic proline residue.


Assuntos
Conotoxinas/química , Sequência de Aminoácidos , Animais , Dicroísmo Circular , Conotoxinas/genética , Conotoxinas/toxicidade , Concentração de Íons de Hidrogênio , Espectroscopia de Ressonância Magnética , Modelos Moleculares , Dados de Sequência Molecular , Antagonistas Nicotínicos/química , Antagonistas Nicotínicos/toxicidade , Conformação Proteica , Soluções , Termodinâmica
15.
J Chromatogr B Biomed Sci Appl ; 737(1-2): 119-30, 2000 Jan 14.
Artigo em Inglês | MEDLINE | ID: mdl-10681048

RESUMO

The purification of a eukaryotic membrane protein has been achieved using a prokaryotic expression system. Bovine cytochrome b5 is an integral membrane protein (Mr approximately 16500). It comprises of a globular haem containing catalytic domain positioned at the N-terminus of the protein and a hydrophobic membrane binding segment at the C-terminus. The membrane binding domain (MBD) is resistant to purification using conventional strategies that have proved successful in isolating the soluble haem containing fragment. We report here a versatile purification method for the isolation of the MBD involving a gene fusion system. The fusion protein incorporates thioredoxin at the amino terminus and six histidines as the metal affinity binding site followed by cytochrome b5 in a pET expression system. This supports high level expression of cytochrome b5 in E. coli C43(DE3) cells. The fusion protein is effectively solubilised from lysed cells with Triton X-100. A step gradient elution with imidazole under non-denaturing conditions on a His-Bind nickel chelate affinity column, saturated with proteins as a crude cell extract, purified the protein in a single step. Proteolytic digestion of pure fusion protein, with trypsin, yielded the MBD. This fragment was further purified by RP-HPLC to a final yield of approximately 10 mg/l.


Assuntos
Cromatografia Líquida de Alta Pressão/métodos , Citocromos b5/isolamento & purificação , Sequência de Bases , Membrana Celular/metabolismo , Citocromos b5/genética , Citocromos b5/metabolismo , Primers do DNA , Eletroforese em Gel de Poliacrilamida , Escherichia coli , Hidrólise , Níquel , Ligação Proteica , Proteínas Recombinantes de Fusão/genética , Proteínas Recombinantes de Fusão/isolamento & purificação , Proteínas Recombinantes de Fusão/metabolismo , Tripsina/metabolismo
16.
Biochemistry ; 38(43): 14352-62, 1999 Oct 26.
Artigo em Inglês | MEDLINE | ID: mdl-10572010

RESUMO

The guanidine hydrochloride- (GuHCl-) induced unfolding and refolding of a recombinant domain of bovine microsomal cytochrome b(5) containing the first 104 amino acid residues has been characterized by both transient and equilibrium spectrophotometric methods. The soluble domain is reversibly unfolded and the equilibrium reaction may be monitored by changes in absorbance and fluorescence that accompany denaturation of the native protein. Both probes reveal a single cooperative transition with a midpoint at 3 M GuHCl and lead to a value for the protein stability (DeltaG(uw)) of 26.5 kJ mol(-1). This stability is much higher than that reported for the corresponding form of the apoprotein (approximately 7 kJ mol(-1)). Transient changes in fluorescence and absorbance during protein unfolding exhibit biphasic profiles. A fast phase occupying approximately 30% of the total amplitude is observed at high denaturant concentrations and becomes the dominant process within the transition region. The rates associated with each process show a linear dependency on GuHCl concentration, and at zero denaturant concentration the unfolding rates (k(uw)) are 4.5 x 10(-5) s(-1) and 5.2 x 10(-6) s(-1) at 25 degrees C. The pattern of unfolding is not correlated with covalent heterogeneity, since a wide range of variants and site-directed mutants exhibit identical profiles, nor is the unfolding correlated with cis-trans Pro isomerization in the native state. In comparison with the apo form of cytochrome b(5), the kinetics of refolding and unfolding are more complex and exhibit very different transition states. The data support a model for unfolding in which heme-protein interactions give rise to two discernible rates of unfolding. From an analysis of the activation parameters associated with each process it is established that two structurally similar transition states differing by less than 5 kJ mol(-1) exist in the unfolding reaction. Protein refolding exhibits monophasic kinetics but with distinct curvature apparent in plots of ln k(obs) versus denaturant concentration. The data are interpreted in terms of alternative routes for protein folding in which a "fast track" leads to the rapid ordering of structure around Trp26 for refolding while a slower route requires additional reorganization around the hydrophobic core.


Assuntos
Citocromos b5/química , Dobramento de Proteína , Animais , Bovinos , Guanidina , Holoenzimas/química , Cinética , Conformação Proteica , Desnaturação Proteica , Proteínas Recombinantes/química , Espectrometria de Fluorescência , Temperatura , Termodinâmica , Triptofano/química
17.
Biochemistry ; 38(29): 9533-40, 1999 Jul 20.
Artigo em Inglês | MEDLINE | ID: mdl-10413531

RESUMO

The refolding and unfolding kinetics of a soluble domain of apocytochrome b5 extending from residue 1 to 104 have been characterized using stopped flow and equilibrium-based fluorescence methods. The isolated apoprotein unfolds reversibly in the presence of GuHCl. From cooperative unfolding curves, the conformational stability (Delta G(uw)), in the absence of denaturant, is estimated to be 11.6 +/- 1.5 kJ mol-1 at 10 degrees C. The stability of apocytochrome b5 is lower than that of the corresponding form of the holoprotein (Delta G approximately 25 kJ mol-1) and exhibits a transition midpoint at 1.6 M GuHCl. Kinetic studies support the concept of a two-state model with both unfolding and refolding rates showing an exponential dependence on denaturant concentration with no evidence of the formation of transient intermediates in either limb of the chevron plot. Apocytochrome b5 is therefore an example of a protein in which both kinetics and equilibria associated with folding are described by a two-state model. The values of mku and mkf obtained from kinetic analysis are an indication of a transition state (mku/meq of 0.29) that resembles the native form by retaining similar solvent accessibility and many of the noncovalent interactions found in the apoprotein. The changes in heat capacity support a transition state that resembles the apoprotein with a value for Delta Cpf of -3.6 kJ mol-1 K-1 estimated for the refolding reaction. From these measurements, a model of refolding that involves the rapid nucleation of hydrophobic residues around Trp26 is suggested as a major event in the formation of the native apoprotein.


Assuntos
Apoproteínas/química , Apoproteínas/metabolismo , Grupo dos Citocromos b/química , Grupo dos Citocromos b/metabolismo , Dobramento de Proteína , Animais , Bovinos , Citocromos b , Estabilidade Enzimática , Guanidina , Cinética , Desnaturação Proteica , Espectrometria de Fluorescência , Temperatura , Termodinâmica
20.
FEBS Lett ; 412(3): 610-4, 1997 Aug 04.
Artigo em Inglês | MEDLINE | ID: mdl-9276476

RESUMO

A comparison of the primary sequences of the heme binding domains of bovine and rat microsomal cytochrome reveal differences at only six residues. These residues must therefore provide the origin for the observed variation in the ratio of the heme orientational isomers, the equilibrium constant of which ranges from approximately 9 in the bovine protein to 1.6 for rat cytochrome b5. Residues 7, 20, 21, and 30 are distant from the exposed heme edge whilst Leu27 and Phe78 are located close to different parts of the porphyrin macrocycle. 1H NMR spectra of the heme and heme ligand resonances of a recombinant tobacco cytochrome b5 extending from Gly1 to Lys89 suggest, in combination with NMR data acquired for other forms of cytochrome b5 and an inspection of their sequence homology, that the identity of residue 78 influences the relative ratios of heme isomers. The Gly1-Lys89 domain of tobacco cytochrome b5 has two equally abundant heme orientational isomers but retains the leucine side chain at position 27 whilst phenylalanine 78 is replaced by tyrosine. A more direct role for residue 78 in modulating the heme ratio is shown by site directed mutagenesis of bovine microsomal cytochrome b5 where the mutation Phe78 > Tyr shifts the equilibrium constant for the heme orientational isomers from 9 to 3.5. Whilst the ratio is clearly shifted towards that exhibited by the rat protein the incomplete transition suggested the involvement of other residues. The mutation of Leu27 > Val was shown to result in a slightly smaller change in ratios of each isomer (from 9 to 4.0). Together these results point to the importance of these residues in modulating the ratio of heme isomers.


Assuntos
Citocromos b5/química , Citocromos b5/genética , Heme/química , Heme/genética , Mutagênese Sítio-Dirigida , Sequência de Aminoácidos , Animais , Bovinos , Cristalografia por Raios X , Espectroscopia de Ressonância Magnética , Microssomos/enzimologia , Dados de Sequência Molecular , Fenilalanina , Plantas Tóxicas , Ratos , Nicotiana , Tirosina
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