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BACKGROUND: Faecal immunochemical test (FIT) usage for symptomatic patients is increasing, but variations in use caused by sociodemographic factors are unknown. A clinical pathway for colorectal cancer (CRC) was introduced in primary care for symptomatic patients in November 2017. The pathway was commissioned to provide GPs with direct access to FITs. AIM: To identify whether sociodemographic factors affect FIT return in symptomatic patients. DESIGN AND SETTING: A retrospective study was undertaken in Nottingham, UK, following the introduction of FIT as triage tool in primary care. It was mandated for all colorectal referrals (except rectal bleeding or mass) to secondary care. FIT was used, alongside full blood count and ferritin, to stratify CRC risk. METHOD: All referrals from November 2017 to December 2021 were retrospectively reviewed. Sociodemographic factors affecting FIT return were analysed by multivariate logistic regression. RESULTS: A total of 35 289 (90.7%) patients returned their index FIT, while 3631 (9.3%) did not. On multivariate analysis, males were less likely to return an FIT (odds ratio [OR] 1.11, 95% confidence interval [CI] = 1.03 to 1.19). Patients aged ≥65 years were more likely to return an FIT (OR 0.78 for non-return, 95% CI = 0.72 to 0.83). Unreturned FIT more than doubled in the most compared with the least deprived quintile (OR 2.20, 95% CI = 1.99 to 2.43). Patients from Asian (OR 1.82, 95% CI = 1.58 to 2.10), Black (OR 1.21, 95% CI = 0.98 to 1.49), and mixed or other ethnic groups (OR 1.29, 95% CI = 1.05 to 1.59) were more likely to not return an FIT compared with patients from a White ethnic group. A total of 599 (1.5%) CRCs were detected; 561 in those who returned a first FIT request. CONCLUSION: FIT return in those suspected of having CRC varied by sex, age, ethnic group, and socioeconomic deprivation. Strategies to mitigate effects on FIT return and CRC detection should be considered as FIT usage expands.
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Neoplasias Colorrectales , Masculino , Humanos , Estudios Retrospectivos , Neoplasias Colorrectales/diagnóstico , Inmunoquímica , Detección Precoz del Cáncer , Sangre Oculta , Atención Primaria de Salud , Heces/química , Sensibilidad y Especificidad , Hemoglobinas/análisis , ColonoscopíaRESUMEN
BACKGROUND: The use of artificial intelligence (AI) in decision-making around knee replacement surgery is increasing, and this technology holds promise to improve the prediction of patient outcomes. Ambiguity surrounds the definition of AI, and there are mixed views on its application in clinical settings. OBJECTIVE: In this study, we aimed to explore the understanding and attitudes of patients who underwent knee replacement surgery regarding AI in the context of risk prediction for shared clinical decision-making. METHODS: This qualitative study involved patients who underwent knee replacement surgery at a tertiary referral center for joint replacement surgery. The participants were selected based on their age and sex. Semistructured interviews explored the participants' understanding of AI and their opinions on its use in shared clinical decision-making. Data collection and reflexive thematic analyses were conducted concurrently. Recruitment continued until thematic saturation was achieved. RESULTS: Thematic saturation was achieved with 19 interviews and confirmed with 1 additional interview, resulting in 20 participants being interviewed (female participants: n=11, 55%; male participants: n=9, 45%; median age: 66 years). A total of 11 (55%) participants had a substantial postoperative complication. Three themes captured the participants' understanding of AI and their perceptions of its use in shared clinical decision-making. The theme Expectations captured the participants' views of themselves as individuals with the right to self-determination as they sought therapeutic solutions tailored to their circumstances, needs, and desires, including whether to use AI at all. The theme Empowerment highlighted the potential of AI to enable patients to develop realistic expectations and equip them with personalized risk information to discuss in shared decision-making conversations with the surgeon. The theme Partnership captured the importance of symbiosis between AI and clinicians because AI has varied levels of interpretability and understanding of human emotions and empathy. CONCLUSIONS: Patients who underwent knee replacement surgery in this study had varied levels of familiarity with AI and diverse conceptualizations of its definitions and capabilities. Educating patients about AI through nontechnical explanations and illustrative scenarios could help inform their decision to use it for risk prediction in the shared decision-making process with their surgeon. These findings could be used in the process of developing a questionnaire to ascertain the views of patients undergoing knee replacement surgery on the acceptability of AI in shared clinical decision-making. Future work could investigate the accuracy of this patient group's understanding of AI, beyond their familiarity with it, and how this influences their acceptance of its use. Surgeons may play a key role in finding a place for AI in the clinical setting as the uptake of this technology in health care continues to grow.
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Artroplastia de Reemplazo de Rodilla , Procedimientos Ortopédicos , Humanos , Femenino , Masculino , Anciano , Inteligencia Artificial , Toma de Decisiones Clínicas , ComunicaciónRESUMEN
BACKGROUND: Thirty-day readmission is an increasingly important problem for total knee arthroplasty (TKA) patients. The aim of this study was to develop a risk prediction model using machine learning and clinical insight for 30-day readmission in primary TKA patients. METHOD: Data used to train and internally validate a multivariable predictive model were obtained from a single tertiary referral centre for TKA located in Victoria, Australia. Hospital administrative data and clinical registry data were utilised, and predictors were selected through systematic review and subsequent consultation with clinicians caring for TKA patients. Logistic regression and random forest models were compared to one another. Calibration was evaluated by visual inspection of calibration curves and calculation of the integrated calibration index (ICI). Discriminative performance was evaluated using the area under the receiver operating characteristic curve (AUC-ROC). RESULTS: The models developed in this study demonstrated adequate calibration for use in the clinical setting, despite having poor discriminative performance. The best-calibrated readmission prediction model was a logistic regression model trained on administrative data using risk factors identified from systematic review and meta-analysis, which are available at the initial consultation (ICI = 0.012, AUC-ROC = 0.589). Models developed to predict complications associated with readmission also had reasonable calibration (ICI = 0.012, AUC-ROC = 0.658). CONCLUSION: Discriminative performance of the prediction models was poor, although machine learning provided a slight improvement. The models were reasonably well calibrated, meaning they provide accurate patient-specific probabilities of these outcomes. This information can be used in shared clinical decision-making for discharge planning and post-discharge follow up.
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A skeleton discovered in Grand Forks, North Dakota was purported to belong to Clelland "Clell" Miller, a James-Younger gang member, who was killed during the Northfield Bank robbery on September 7, 1876. A 3-D image from a computer tomography (CT) scan of the skull was obtained, and a craniofacial superimposition was conducted to determine if the skull could belong to Miller. The superimposition method used in this case was to overlay the CT image of the skull onto Miller's postmortem photograph. In addition to the craniofacial superimposition, the images were juxtaposed to compare similarities or differences in facial morphology between the skull and photograph. Superimposition methods can be used to exclude identifications; however, they should not be used as a conclusive method for identification. In this case, there were sufficient similarities between the skull and Miller's photograph; therefore, the skull could not be eliminated as possibly being that of Miller.
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Identificación Biométrica/métodos , Cara/anatomía & histología , Imagenología Tridimensional , Fotograbar , Cráneo/diagnóstico por imagen , Antropología Forense/métodos , Historia del Siglo XIX , Humanos , Procesamiento de Imagen Asistido por Computador , Masculino , Programas Informáticos , Tomografía Computarizada por Rayos XRESUMEN
BACKGROUND: Patients with secondary hyperparathyroidism and on dialysis are more likely to die of cardiovascular disease than the general population; and we have reported that near-total parathyroidectomy (NTPTX) reduces that mortality rate. Patients on dialysis experience an average of a 15% increase in coronary calcification yearly, contributing to cardiovascular death. Cardiac computed tomography (CT) enables objective measuring of coronary calcium. The purpose of our study was to determine the impact of NTPTX on coronary artery calcium score (CACS). METHODS: CACS measurement was performed in patients with stage 5 chronic kidney disease before and after NTPTX from 2001 to 2008. Demographics, morbidities, CACS, outcomes, intact parathyroid hormone (PTH) measurements in follow-up (mean, 5.1 years) were maintained in an institutional review board-approved prospective database. Of 31 patients, 19 (61%) returned for a follow-up coronary CT. RESULTS: Preoperative mean PTH level and CACS were 1,794 ± 943 pg/mL and 979 ± 079, respectively; postoperatively, PTH and CACS were 321 ± 244 pg/mL (P < .001) and 1,285 ± 1,577 (P = .044), respectively. CACS was stable or reduced (<10% per year) in 6 of 19 patients (32%), and 42% of patients (n = 8) had nearly undetectable (<1% per year) change in CACS after NTPTX. In patients with stable CACS, mean postoperative PTH was 251 versus 516 pg/mL in patients with increasing CACS (P = .02). In patients with recurrent hyperparathyroidism (PTH > 400) compared with patients with stable postoperative PTH, CACS increased by 804 ± 1082 versus 16 ± 84 (P = .02). CONCLUSION: Successful NTPTX with stable postoperative PTH levels is associated with stabilization of CACS in patients with severe secondary hyperparathyroidism undergoing hemodialysis, which could contribute to the improved survival seen after NTPTX.
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Calcio/metabolismo , Vasos Coronarios/metabolismo , Paratiroidectomía/métodos , Diálisis Renal/efectos adversos , Adulto , Anciano , Enfermedades Cardiovasculares/etiología , Enfermedades Cardiovasculares/metabolismo , Enfermedades Cardiovasculares/prevención & control , Vasos Coronarios/diagnóstico por imagen , Femenino , Humanos , Hiperparatiroidismo Secundario/etiología , Hiperparatiroidismo Secundario/metabolismo , Hiperparatiroidismo Secundario/prevención & control , Fallo Renal Crónico/complicaciones , Fallo Renal Crónico/metabolismo , Fallo Renal Crónico/terapia , Masculino , Persona de Mediana Edad , Hormona Paratiroidea/sangre , Estudios Prospectivos , Recurrencia , Factores de Riesgo , Tomografía Computarizada por Rayos XRESUMEN
The reaction of 2,2'-bipyridine (bpy) with monomeric chromium(II) precursors was used to prepare the S = 1 complexes Cr(tBu-acac)2(bpy) (1) and (η(5)-Cp)(η(1)-Cp)Cr(bpy) (3), as well as the S = 2 compound Cr[N(SiMe3)2]2(bpy) (4). The crystallographically determined bond lengths indicate that the bpy ligands in 1 and 3 are best regarded as radical anions, while 4 shows no structural evidence for electron transfer from Cr(II) to the neutral bpy ligand.
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Compuestos de Cromo/química , Compuestos Organometálicos/química , Piridinas/química , Cristalografía por Rayos X , Radicales Libres/síntesis química , Radicales Libres/química , Ligandos , Modelos Moleculares , Estructura Molecular , Compuestos Organometálicos/síntesis químicaRESUMEN
Duct tape is sometimes recovered as physical evidence in crimes. The purpose of this study was to determine the quality of latent prints on the adhesive and non-adhesive surfaces of duct tape samples that were separated using three methods. Three hundred donor fingerprint impressions were deposited on duct tape. Sections of duct tape were affixed to sections of cardboard and a fingerprint placed on the non-adhesive surface of the tape. A second layer of duct tape was prepared and a fingerprint placed on the adhesive side of the tape and then the tape was affixed to the piece of tape on the cardboard. After a 24-h period, the samples were separated using gradual force, liquid nitrogen applied with a cryogun and an adhesive neutralizer to separate the layers of tape. The recovered fingerprints were processed with a fingerprint powder suspension method. The recovered fingerprint images were evaluated and rated as +1, +2, or +3. The liquid nitrogen spray separation method yielded the highest number of +3 prints.
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Adhesivos , Dermatoglifia , Congelación , Nitrógeno , Polvos , Suspensiones , Femenino , Heptanos , Humanos , Aumento de la Imagen , Microscopía , Persona de Mediana Edad , SolventesRESUMEN
Conducting polymer (polyaniline) sheets are shown to be active substrates to promote the growth of nanostructured silver thin films with highly tunable morphologies. Using the spontaneous electroless deposition of silver, we show that a range of nanostructured metallic features can be controllably and reproducibly formed over large surface areas. The structural morphology of the resulting metal-polymer nanocomposite is demonstrated to be sensitive to experimental parameters such as ion concentration, temperature, and polymer processing and can range from densely packed oblate nanosheets to bulk crystalline metals. The deposition mechanisms are explained using a diffusion-limited aggregation (DLA) model to describe the semi-fractal-like growth of the metal nanostructures. We find these composite films to exhibit strong surface-enhanced Raman (SERS) activity, and the nanostructured features are optimized with respect to SERS activity using a self-assembled monolayer of mercapto-benzoic acid as a model Raman reporter. SERS enhancements are estimated to be on the order of 10(7). Through micro-Raman SERS mapping, these materials are shown to exhibit uniform SERS responses over macroscopic areas. These metal-polymer nanocomposites benefit from the underlying polymer's processability to yield SERS-active materials of almost limitless shape and size and show significant promise for future SERS-based sensing and detection schemes.
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Saw marks on bone have been routinely reported in dismemberment cases. When saw blade teeth contact bone and the bone is not completely sawed into two parts, bone fragments are removed forming a channel or kerf. Therefore, kerf width can approximate the thickness of the saw blade. The purpose of this study is to evaluate 100 saw kerf widths in bone produced by ten saw types to determine if a saw can be eliminated based on the kerf width. Five measurements were taken from each of the 100 saw kerfs to establish an average thickness for each kerf mark. Ten cuts were made on 10 sections of bovine bone, five with human-powered saws and five with mechanical-powered saws. The cuts were examined with a stereoscopic microscope utilizing digital camera measuring software. Two statistical cumulative logistic regression models were used to analyze the saw kerf data collected. In order to estimate the prediction error, repeated stratified cross-validation was applied in analyzing the kerf mark data. Based on the two statistical models used, 70-90% of the saws could be eliminated based on kerf width.
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Huesos/lesiones , Desmembramiento de Cadáver , Patologia Forense/métodos , Animales , Bovinos , Interpretación Estadística de Datos , Diagnóstico por Imagen , Modelos AnimalesRESUMEN
We report an investigation of complexes of the type M(2)(dmp)(4) (M = Mo, Cr; dmp = 2,6-dimethoxyphenyl) using resonance Raman (RR) spectroscopy, Cr isotopic substitution, and density functional theory (DFT) calculations. Assignment of the Mo-Mo stretching vibration in the Mo(2) species is straightforward, as evidenced by a single resonance-enhanced band at 424 cm(-1), consistent with an essentially unmixed metal-metal stretch, and overtones of this vibration. On the other hand, the Cr(2) congener has no obvious metal-metal stretching mode near 650-700 cm(-1), where empirical predictions based on the Cr-Cr distance as well as DFT calculations suggest that this vibration should appear if unmixed. Instead, three bands are observed at 345, 363, and 387 cm(-1) that (a) have relative RR intensities that are sensitive to the Raman excitation frequency, (b) exhibit overtones and combinations in the RR spectra, and (c) shift in frequency upon isotopic substitution ((50)Cr and (54)Cr). DFT calculations are used to model the vibrational data for the Mo(2) and Cr(2) systems. Both the DFT results and empirical predictions are in good agreement with experimental observations in the Mo(2) complex, but both, while mutually consistent, differ radically from experiment in the Cr(2) complex. Our experimental and theoretical results, especially the Cr isotope shifts, clearly demonstrate that the potential energy of the Cr-Cr stretching coordinate is distributed among several normal modes having both Cr-Cr and Cr-ligand character. The general significance of these results in interpreting spectroscopic observations in terms of the nature of metal-metal multiple bonding is discussed.
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Cromo/química , Molibdeno/química , Compuestos Organometálicos/química , Teoría Cuántica , Absorción , Electrones , Isótopos , Modelos Moleculares , Conformación Molecular , Espectrometría RamanRESUMEN
We report the use of photoinduced electron transfer to drive reductive cleavage of an ester to produce bilayer-forming molecules; specifically, visible photolysis in a mixture of a decanoic acid ester precursor, hydrogen donor molecules, and a ruthenium-based photocatalyst that employs a linked nucleobase (8-oxo-guanine) as an electron donor generates decanoic acid. The overall transformation of the ester precursor to yield vesicles represents the use of an external energy source to convert nonstructure forming molecules into amphiphiles that spontaneously assemble into vesicles. The core of our chemical reaction system uses an 8-oxo-G-Ru photocatalyst, a derivative of [tris(2,2'-bipyridine)-Ru(II)](2+).
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Suspicious circumstances surrounding the death of wealthy socialite Mary Lily "Lil'" Kenan Flagler Bingham in 1917 prompted a secret autopsy conducted by renowned physicians at the request of her relatives. Mrs Bingham, who was formerly married to railroad magnate, Henry Flagler, was among America's richest people at the time of her death. Mary Lil's untimely death occurred approximately six months after her marriage to Judge Robert "Bob" Worth Bingham, a college boyfriend whom she married three years after Flagler's death. In order to establish Mary Lil's medical condition prior to her death, a book about Mary Lil's life written by Pulitzer Prize author, David Chandler and articles from the New York Times; The Louisville Courier Journal, a Kentucky newspaper; and Mary Lil's hometown newspaper, The Morning Star, in Wilmington, North Carolina were examined. Although a team of medical experts performed a secret autopsy following her death and released their findings to her family, the examination and tests results remain undisclosed to the public.
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Personajes , Patologia Forense/métodos , Analgésicos Opioides/envenenamiento , Intoxicación por Arsénico/diagnóstico , Libros , Dolor en el Pecho/etiología , Certificado de Defunción , Diagnóstico Diferencial , Exhumación , Femenino , Toxicología Forense , Historia del Siglo XX , Humanos , Morfina/envenenamiento , Infarto del Miocardio/diagnóstico , Periódicos como Asunto , Intoxicación/diagnóstico , Investigación , Estados UnidosRESUMEN
A classification system and identification key for .177 caliber air gun pellets was developed based on a five-class characteristic criterion. Sixty-eight pellet types from 15 companies were examined and compared. A classification system was developed based on the pellets' head shapes, skirt types, lengths, weights, and other markings or observations. In some cases, when a pellet is recovered from a crime scene, product brand identification may aid the investigation. Even though all product brands cannot be identified, various brands of pellets can be eliminated based on a pellet's class characteristics. The pellet producers in this study were located in the following countries: China, Czech Republic, England, Korea, Spain, and the United States. An identification key can be used for possible pellet identification or elimination.
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In using infrared or infrared-enhanced photography to examine gunshot residue (GSR) on dark-colored clothing, the GSR particles are microscopically examined directly on the fabric followed by the modified Griess test (MGT) for nitrites. In conducting the MGT, the GSR is transferred to treated photographic paper for visualization. A positive reaction yields an orange color on specially treated photographic paper. The examiner also evaluates the size of the powder pattern based on the distribution of nitrite reaction sites or density. A false-positive reaction can occur using the MGT due to contaminants or dyes that produce an orange cloud reaction as well. A method for enhancing visualization of the pattern produced by burned and partially unburned powder is by treatment of the fabric with a solution of sodium hypochlorite. In order to evaluate the results of sodium hypochlorite treatment for GSR visualization, the MGT was used as a reference pattern. Enhancing GSR patterns on dark or multicolored clothing was performed by treating the fabric with an application of 5.25% solution of sodium hypochlorite. Bleaching the dyes in the fabric enhances visualization of the GSR pattern by eliminating the background color. Some dyes are not affected by sodium hypochlorite; therefore, bleaching may not enhance the GSR patterns in some fabrics. Sodium hypochlorite provides the investigator with a method for enhancing GSR patterns directly on the fabric. However, this study is not intended to act as a substitute for the MGT or Sodium Rhodizonate test.
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Microperoxidase-11 has been immobilized on siliceous materials MCM-41 and SBA-15 and on amino-functionalized SBA-15. Resonance Raman spectroscopy has provided solid evidence that the exogenous species occupy the pores of the mesoporous silica materials. Photoreduction of the microperoxidase-11 Fe(III) center has been observed to occur in the immobilized samples and results in a long-lived stable reduced heme. Reoxidation of the heme occurs upon addition of oxygen, and the redox cycle can be repeated numerous times. The source of the electron resulting in reduction of the heme is proposed to originate from the silica matrix, and functionalization of silica surface is suggested to facilitate electron transfer to the heme.
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Hemo/química , Péptidos/química , Peroxidasas/química , Anaerobiosis , Cristalografía por Rayos X , Composición de Medicamentos , Electrones , Hierro/química , Nanotecnología , Oxidación-Reducción , Fotoquímica , Fotones , Porfirinas/química , Espectrofotometría Ultravioleta , Espectrometría RamanRESUMEN
FTIR difference spectroscopy is used to reveal changes in the internal structure and amino acid protonation states of bovine cytochrome c oxidase (CcO) that occur upon photolysis of the CO adduct of the two-electron reduced (mixed valence, MV) and four-electron reduced (fully reduced, FR) forms of the enzyme. FTIR difference spectra were obtained in D(2)O (pH 6-9.3) between the MV-CO adduct (heme a(3) and Cu(B) reduced; heme a and Cu(A) oxidized) and a photostationary state in which the MV-CO enzyme is photodissociated under constant illumination. In the photostationary state, part of the enzyme population has heme a(3) oxidized and heme a reduced. In MV-CO, the frequency of the stretch mode of CO bound to ferrous heme a(3) decreases from 1965.3 cm(-1) at pH* =7 to 1963.7 cm(-1) at pH* 9.3. In the CO adduct of the fully reduced enzyme (FR-CO), the CO stretching frequency is observed at 1963.46+/-0.05 cm(-1), independent of pH. This indicates that in MV-CO there is a group proximal to heme a that deprotonates with a pK(a) of about 8.3, but that remains protonated over the entire pH* range 6-9.3 in FR-CO. The pK(a) of this group is therefore strongly coupled to the redox state of heme a. Following photodissociation of CO from heme a(3) in MV oxidases, the extent of electron transfer from heme a(3) to heme a shows a pH-dependent phase between pH 7 and 9, and a pH-independent phase at all pH's. The FTIR difference spectrum resulting from photolysis of MV-CO exhibits vibrational features of the protein backbone and side chains associated with (1) the loss of CO by the a(3) heme in the absence of electron transfer, (2) the pH-independent phase of the electron transfer, and (3) the pH-dependent phase of the electron transfer. Many infrared features change intensity or frequency during both electron transfer phases and thus appear as positive or negative features in the difference spectra. In particular, a negative band at 1735 cm(-1) and a positive band at 1412 cm(-1) are consistent with the deprotonation of the acidic residue E242. Positive features at 1552 and 1661 cm(-1) are due to amide backbone modes. Other positive and negative features between 1600 and 1700 cm(-1) are consistent with redox-induced shifts in heme formyl vibrations, and the redox-linked protonation of an arginine residue, accompanying electron transfer from heme a(3) to heme a. An arginine could be the residue responsible for the pH-dependent shift in the carbonyl frequency of MV-CO. Specific possibilities as to the functional significance of these observations are discussed.
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Complejo IV de Transporte de Electrones/química , Complejo IV de Transporte de Electrones/metabolismo , Animales , Bovinos , Transporte de Electrón , Hemo/química , Técnicas In Vitro , Oxidación-Reducción , Fuerza Protón-Motriz , Espectroscopía Infrarroja por Transformada de FourierRESUMEN
Infrared spectroscopy, isotopic labeling ([(15)N(delta,epsilon)]histidine and ring-deuterated tyrosine), synthetic model studies, and normal mode calculations are employed to search for the spectroscopic signatures of the unique, covalently linked (His N(epsilon)-C(epsilon) Tyr) biring structure in the heme-copper oxidases. The specific enzyme examined is the cytochrome bo(3) quinol oxidase of E. coli. Infrared features of histidine and tyrosine are identified in the frequency regions of imidazole and phenol ring stretching modes (1350-1650 cm(-1)) and C-H and N-H stretching modes as well as overtones and combinations (>3000 cm(-1)). Two of these, at ca. 1480 and 1550 cm(-1), and their combination tones between 3010 and 3040 cm(-1), are definitively identified with the biring structure involving H284 and Y288 in the E. coli enzyme. Studies of a synthetic analogue of the H-Y structure, 4-methylimidazole covalently linked to p-cresol, show that a feature near 1540 cm(-1) is unique to the biring structure and is absent from the infrared spectrum of 4-methylimidazole or p-cresol alone. This feature is readily detectable by infrared difference techniques, and offers a direct spectroscopic probe for potential radical production involving the H-Y structure in the O(2) reduction cycle of the oxidases.
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Hemoproteínas/química , Histidina/química , Oxidorreductasas/química , Tirosina/química , Sitios de Unión , Monóxido de Carbono/química , Grupo Citocromo b , Citocromos/química , Dimerización , Proteínas de Escherichia coli/síntesis química , Proteínas de Escherichia coli/química , Radicales Libres/química , Hemoproteínas/síntesis química , Modelos Químicos , Modelos Moleculares , Oxidorreductasas/síntesis química , Espectrofotometría Infrarroja/métodosRESUMEN
We have used cryogenic difference FTIR and time-resolved step-scan Fourier transform infrared (TR-FTIR) spectroscopies to explore the redox-linked proton-pumping mechanism of heme-copper respiratory oxidases. These techniques are used to probe the structure and dynamics of the heme a(3)-Cu(B) binuclear center and the coupled protein structures in response to the photodissociation of CO from heme Fe and its subsequent binding to and dissociation from Cu(B). Previous cryogenic (80 K) FTIR CO photodissociation difference results were obtained for cytochrome bo(3), the ubiquinol oxidase of Escherichia coli [Puustinen, A., et al. (1997) Biochemistry 36, 13195-13200]. These data revealed a connectivity between Cu(B) and glutamic acid E286, a residue which has been implicated in proton pumping. In the current work, the same phenomenon is observed using the CO adduct of bovine cytochrome aa(3) under cryogenic conditions, showing a perturbation of the equivalent residue (E242) to that in bo(3). Furthermore, using time-resolved (5 micros resolution) step-scan FTIR spectroscopy at room temperature, we observe the same spectroscopic perturbation in both cytochromes aa(3) and bo(3). In addition, we observe evidence for perturbation of a second carboxylic acid side chain, at higher frequency in both enzymes at room temperature. The high-frequency feature does not appear in the cryogenic difference spectra, indicating that the perturbation is an activated process. We postulate that the high-frequency IR feature is due to the perturbation of E62 (E89 in bo(3)), a residue near the opening of the proton K-channel and required for enzyme function. The implications of these results with respect to the proton-pumping mechanism are discussed. Finally, a fast loss of over 60% of the Cu(B)-CO signal in bo(3) is observed and ascribed to one or more additional conformations of the enzyme. This fast conformer is proposed to account for the uninhibited reaction with O(2) in flow-flash experiments.