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Mitchell DM, Wang Y, Alben JO, Shapleigh JP. FT-IR analysis of membranes of Rhodobacter sphaeroides 2.4.3 grown under microaerobic and denitrifying conditions. BIOCHIMICA ET BIOPHYSICA ACTA 1998; 1409:99-105. [PMID: 9838065 DOI: 10.1016/s0005-2728(98)00154-6] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 10/17/2022]
Abstract
Fourier transform infrared spectroscopic analysis of CO binding proteins in Rhodobacter sphaeroides reveals the presence of a membrane-bound nitric oxide reductase (Nor). Nor has been clearly distinguished from the cytochrome oxidases by the temperature-dependence of relaxation following photodissociation of the CO complex at cryogenic temperatures. The center frequency and band shape, 1970 cm-1 and 20-30 cm-1 width at half-peak height, are similar to those reported for resonance Raman spectra of purified Paracoccus denitrificans Nor. Additional evidence is presented to indicate this enzyme is part of dissimilatory nitric oxide metabolism and that one of the genes in the nor operon required for production of an active Nor is not required for protein assembly or heme incorporation.
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Dilworth JP, Mitchell DM. Comparison of the views of junior doctors, consultants and managers on work and training. JOURNAL OF THE ROYAL COLLEGE OF PHYSICIANS OF LONDON 1998; 32:344-50. [PMID: 9762629 PMCID: PMC9663075] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Subscribe] [Scholar Register] [Indexed: 02/09/2023]
Abstract
OBJECTIVE To determine the views of junior hospital doctors on their working conditions, NHS reforms and training, and to compare their views with those of consultants and managers. SUBJECTS A questionnaire was distributed to 52 junior doctors, 19 consultants and 14 middle or senior grade managers in an acute NHS trust. CONCLUSIONS Junior doctors had strong feelings about several areas covered in the questionnaire; in particular, more structured training without the requirement to undertake a higher degree would be welcomed. Shift systems are unpopular and the reduction of 'non-medical' tasks with a reduction in work intensity is perceived to be more important than further reductions in hours available for work.
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Clarke JR, Mitchell DM, Coker RJ, Israel-Biet D. Is the lung important as a privileged site for the human immunodeficiency virus? Thorax 1998; 53:81-2. [PMID: 9624288 PMCID: PMC1758722 DOI: 10.1136/thx.53.2.81] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/03/2022]
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Ghaim JB, Tsatsos PH, Katsonouri A, Mitchell DM, Salcedo-Hernandez R, Gennis RB. Matrix-assisted laser desorption ionization mass spectrometry of membrane proteins: demonstration of a simple method to determine subunit molecular weights of hydrophobic subunits. BIOCHIMICA ET BIOPHYSICA ACTA 1997; 1330:113-20. [PMID: 9408163 DOI: 10.1016/s0005-2736(97)00127-2] [Citation(s) in RCA: 20] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 02/05/2023]
Abstract
Matrix-assisted laser desorption ionization (MALDI) mass spectrometry has been used to obtain accurate molecular weight information for each subunit of several hydrophobic integral membrane proteins: cytochrome bo3 (4 subunits) and cytochrome bd (2 subunits) from E. coli, and the bc1 complex (3 subunits) and the cytochrome c oxidase (3 subunits) from Rhodobacter sphaeroides. The results demonstrate that the MALDI method is a convenient, quick, sensitive and reliable means for obtaining the molecular masses of the subunits of purified multisubunit membrane proteins.
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Adelroth P, Ek MS, Mitchell DM, Gennis RB, Brzezinski P. Glutamate 286 in cytochrome aa3 from Rhodobacter sphaeroides is involved in proton uptake during the reaction of the fully-reduced enzyme with dioxygen. Biochemistry 1997; 36:13824-9. [PMID: 9374859 DOI: 10.1021/bi9629079] [Citation(s) in RCA: 123] [Impact Index Per Article: 4.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/05/2023]
Abstract
The reaction with dioxygen of solubilized fully-reduced wild-type and EQ(I-286) (exchange of glutamate 286 of subunit I for glutamine) mutant cytochrome c oxidase from Rhodobacter sphaeroides has been studied using the flow-flash technique in combination with optical absorption spectroscopy. Proton uptake was measured using a pH-indicator dye. In addition, internal electron-transfer reactions were studied in the absence of oxygen. Glutamate 286 is found in a proton pathway proposed to be used for pumped protons from the crystal structure of cytochrome c oxidase from Paracoccus denitrificans [Iwata et al. (1995) Nature 376, 660-669; E278 in P.d. numbering]. It is the residue closest to the oxygen-binding binuclear center that is clearly a part of the pathway. The results show that the wild-type enzyme becomes fully oxidized in a few milliseconds at pH 7.4 and displays a biphasic proton uptake from the medium. In the EQ(I-286) mutant enzyme, electron transfer after formation of the peroxy intermediate is impaired, CuA remains reduced, and no protons are taken up from the medium. Thus, the results suggest that E(I-286) is necessary for proton uptake after formation of the peroxy intermediate and transfer of the fourth electron to the binuclear center. The results also indicate that the proton uptake associated with formation of the ferryl intermediate controls the electron transfer from CuA to heme a.
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Adelroth P, Mitchell DM, Gennis RB, Brzezinski P. Factors determining electron-transfer rates in cytochrome c oxidase: studies of the FQ(I-391) mutant of the Rhodobacter sphaeroides enzyme. Biochemistry 1997; 36:11787-96. [PMID: 9305969 DOI: 10.1021/bi962824s] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/05/2023]
Abstract
The mechanisms of internal electron transfer and oxygen reduction were investigated in cytochrome c oxidase from Rhodobacter sphaeroides (cytochrome aa3) using site-directed mutagenesis in combination with time-resolved optical absorption spectroscopy. Electron-transfer reactions in the absence of O2 were studied after flash photolysis of CO from the partly-reduced enzyme and the reaction of the fully-reduced enzyme with O2 was studied using the so-called flow-flash technique. Results from studies of the wild-type and mutant enzyme in which phenylalanine-391 of subunit I was replaced by glutamine (FQ(I-391)) were compared. The turnover activity of the mutant enzyme was approximately 2% ( approximately 30 s-1) of that of the wild-type enzyme. After flash photolysis of CO from the partly-reduced mutant enzyme approximately 80% of CuA was reduced, which is a much larger fraction than in the wild-type enzyme, and the rate of this electron transfer was 3.2 x 10(3) s-1, which is significantly slower than in the wild-type enzyme. The redox potentials of hemes a and a3 in the mutant enzyme were found to be shifted by about +30 and -70 mV, respectively, as compared to the wild-type enzyme. During the reaction of the fully-reduced FQ(I-391) mutant enzyme with O2 a rapid kinetic phase with a rate constant of 1.2 x 10(5) s-1, presumably associated with O2 binding, was followed by formation of the P intermediate with electrons from heme a3 and CuB with a rate of approximately 4 x 10(3) s-1, and oxidation of the enzyme with a rate of approximately 30 s-1. The dramatically slower electron transfer between the hemes during O2 reduction in the mutant enzyme is not only due to the slower intrinsic electron transfer, but also due to the altered redox potentials. In addition, the results show that the reduced overall activity of the mutant enzyme is due to the slower electron transfer from heme a to the binuclear center during O2 reduction. The relation between the intrinsic heme a/heme a3 electron-transfer rate and equilibrium constant, and the electron-transfer rate from heme a to the binuclear center during O2 reduction is discussed.
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Fisher EA, Zhou M, Mitchell DM, Wu X, Omura S, Wang H, Goldberg AL, Ginsberg HN. The degradation of apolipoprotein B100 is mediated by the ubiquitin-proteasome pathway and involves heat shock protein 70. J Biol Chem 1997; 272:20427-34. [PMID: 9252351 DOI: 10.1074/jbc.272.33.20427] [Citation(s) in RCA: 241] [Impact Index Per Article: 8.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/05/2023] Open
Abstract
Apolipoprotein B (apoB) is the major protein component of atherogenic lipoproteins of hepatic origin. In HepG2 cells, the standard cell culture model of human hepatic lipoprotein metabolism, there is a limited availability of core lipids in the endoplasmic reticulum for association with nascent apoB. Under these conditions, apoB is partially translocated, interacts with cytosolic Hsp70, and undergoes rapid degradation. We show that increasing the expression of Hsp70 in HepG2 cells promotes apoB degradation. In addition, apoB is polyubiquitinated and its degradation both normally and after Hsp70 induction is blocked by inhibitors of the proteasome. The apoB that accumulates after proteasome inhibition is endoplasmic reticulum-associated and can be assembled into lipoproteins and secreted if new lipid synthesis is stimulated. Thus, apoB is the first example of a wild-type mammalian protein whose secretion is regulated by degradation in the cytosol via the ubiquitin-proteasome pathway. Furthermore, targeting of this secretory protein to the proteasome is regulated by the molecular chaperone Hsp70 and the availability of apoB's lipid-ligands.
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Mitchell DM. Human immunodeficiency virus and lung cancer. Br J Surg 1997; 84:1043-4. [PMID: 9278638 DOI: 10.1002/bjs.1800840803] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/05/2023]
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Mitchell DM. Aspects of HIV infection: current infection control policies for HIV. Monaldi Arch Chest Dis 1997; 52:371-5. [PMID: 9401369] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/05/2023] Open
Abstract
A coherent infection control policy within healthcare facilities designed for patients with human immunodeficiency virus (HIV) infection requires the application of a risk management strategy. The central feature is the adoption of universal precautions whereby it is assumed that all patients could potentially be infected by HIV. The major tenets of this are the adoption of good clinical hygiene and the adoption of agreed infection control policies with a consistent approach throughout the institution. This involves a teaching and training programme, and clearly defined policies to protect individuals from HIV infection itself and infection with other pathogens, in particular tuberculosis. Special attention is required for bronchoscopy and lung function, as well as a coherent and proactive policy regarding chemoprophylaxis for HIV infection following accidental injury such as needlestick.
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Clarke JR, Sohi DK, Maniar JK, Udwadia Z, Mitchell DM. Dual infection with HIV-1 and HIV-2. Thorax 1997; 52:587-8. [PMID: 9227736] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [MESH Headings] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/04/2023]
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37
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Drake WM, Elkin SL, al-Kutoubi A, Mitchell DM, Shaw RJ. Pulmonary artery occlusion by tuberculous mediastinal lymphadenopathy. Thorax 1997; 52:301-2. [PMID: 9093356 PMCID: PMC1758518 DOI: 10.1136/thx.52.3.301] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/04/2023]
Abstract
Two cases of tuberculous mediastinal lymphadenopathy are presented in which the clinical features mimicked those of pulmonary embolism, causing striking abnormalities on radionuclide scintigraphy. It is concluded that tuberculous mediastinal lymphadenopathy should be included in the differential diagnosis of reduced lung perfusion due to proximal pulmonary artery occlusion.
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Zhang X, Rosenstein BS, Wang Y, Lebwohl M, Mitchell DM, Wei H. Induction of 8-oxo-7,8-dihydro-2'-deoxyguanosine by ultraviolet radiation in calf thymus DNA and HeLa cells. Photochem Photobiol 1997; 65:119-24. [PMID: 9066291 DOI: 10.1111/j.1751-1097.1997.tb01886.x] [Citation(s) in RCA: 98] [Impact Index Per Article: 3.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/03/2023]
Abstract
The levels of 8-oxo-7,8-dihydro-2'-deoxyguanosine (8-oxodGuo) in purified calf thymus DNA and HeLa cells were measured following exposure to either UVC, UVB or UVA wavelengths. This DNA damage was quantitated using HPLC coupled with an electrochemical detector. The 8-oxodGuo was induced in purified DNA in a linear dose-dependent fashion by each portion of the UV spectrum at yields of 100, 0.46 and 0.16 8-oxodGuo per 10(5) 2'-deoxyguanosine (dGuo) per kJ/m2 for UVC, UVB and UVA, respectively. However, the amount of 8-oxodGuo in HeLa cells irradiated with these UV sources decreased to approximately 2.0, 0.013 and 0.0034 8-oxodGuo per 10(5) dGuo per kJ/m2, respectively. In contrast, the levels of cyclobutyl pyrimidine dimers were similar in both irradiated DNA and cells. Therefore, 8-oxodGuo is induced in cells exposed to wavelengths throughout the UV spectrum although it appears that protective precesses exist within cells that reduce the UV-induced formation of this oxidative DNA damage. Cell survival was also measured and the number of dimers or 8-oxodGuo per genome per lethal event determined. These calculations are consistent with the conclusion that dimers play a major role in cell lethality for UVC- or UVB-irradiated cells but only a minor role in cells exposed to UVA wavelengths. In addition, it was found that the relative yield of 8-oxodGuo to dimers increased nearly 1000-fold in both UVA-irradiated cells and DNA compared with cells subjected to either UVC or UVB. These results are supportive of the hypothesis that 8-oxodGuo, and possible other forms of oxidative damage, play an important role in the induction of biological effects caused by wavelengths in the UVA portion of the solar spectrum.
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Mitchell DM, Müller JD, Gennis RB, Nienhaus GU. FTIR study of conformational substates in the CO adduct of cytochrome c oxidase from Rhodobacter sphaeroides. Biochemistry 1996; 35:16782-8. [PMID: 8988016 DOI: 10.1021/bi961722z] [Citation(s) in RCA: 15] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/03/2023]
Abstract
Fourier transform infrared (FTIR) spectroscopy of cytochrome c oxidase from Rhodobacter sphaeroides reveals multiple CO stretch bands that are associated with different conformational substates of the enzyme. Here we report the temperature dependence of the infrared bands for the CO bound to the Fea3 heme iron and to CuB. We have also studied the kinetics of ligand return from Fea3 to CuB using temperature derivative spectroscopy (TDS). Two classes of substates (alpha/beta) can be distinguished from their different properties with regard to the width of the IR band, the temperature dependence of the peak position, and the peak of the enthalpy distribution. The pronounced temperature dependence of the stretch frequencies in the beta conformation and the lack thereof in the alpha conformation implies very different dynamic behavior in the active site and reflects structural differences between the two conformations, most likely a shift of the position of CuB in response to a change in its stereochemical environment. Similar conformational changes will be necessary during the catalytic cycle of the enzyme when dioxygen is bound in the active site.
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Mitchell DM, Fetter JR, Mills DA, Adelroth P, Pressler MA, Kim Y, Aasa R, Brzezinski P, Malmström BG, Alben JO, Båbcock GT, Ferguson-Miller S, Gennis RB. Site-directed mutagenesis of residues lining a putative proton transfer pathway in cytochrome c oxidase from Rhodobacter sphaeroides. Biochemistry 1996; 35:13089-93. [PMID: 8855945 DOI: 10.1021/bi961416l] [Citation(s) in RCA: 31] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/02/2023]
Abstract
Several putative proton transfer pathways have been identified in the recent crystal structures of the cytochrome oxidases from Paracoccus denitrificans [Iwata et al. (1995) Nature 376, 660-669] and bovine [Tsukihara (1996) Science 272, 1138-1144]. A series of residues along one face of the amphiphilic transmembrane helix IV lie in one of these proton transfer pathways. The possible role of these residues in proton transfer was examined by site-directed mutagenesis. The three conserved residues of helix IV that have been implicated in the putative proton transfer pathway (Ser-201, Asn-207, and Thr-211) were individually changed to alanine. The mutants were purified, analyzed for steady-state turnover rate and proton pumping efficiency, and structurally probed with resonance Raman spectroscopy and FTIR difference spectroscopy. The mutation of Ser-201 to alanine decreased the enzyme turnover rate by half, and was therefore further characterized using EPR spectroscopy and rapid kinetic methods. The results demonstrate that none of these hydrophilic residues are essential for proton pumping or oxygen reduction activities, and suggest a model of redundant or flexible proton transfer pathways. Whereas previously reported mutants at the start of this putative channel (e.g., Asp-132-Asn) dramatically influence both enzyme turnover and coupling to proton pumping, the current work shows that this is not the case for all residues observed in this channel.
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Boffa MJ, Smith A, Chalmers RJ, Mitchell DM, Rowan B, Warnes TW, Shomaf M, Haboubi NY. Serum type III procollagen aminopeptide for assessing liver damage in methotrexate-treated psoriatic patients. Br J Dermatol 1996; 135:538-44. [PMID: 8915142] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/03/2023]
Abstract
This study was designed to establish whether measurement of a serological marker of fibrosis might reduce the need for liver biopsy in psoriatic patients receiving methotrexate (MTX). Levels of type III procollagen aminopeptide (PIIINP-O and PIIINP-B) and laminin P1 (LamP1-B) were measured in 147 serum samples taken at the time of liver biopsy in 87 patients receiving long-term MTX treatment for severe psoriasis. Biopsies were classified as: (1) normal, (2) steatosis, (3) inflammation, (4) fibrosis, or (5) cirrhosis. Groups 3-5 were considered to show clinically relevant abnormality. Compared with controls, PIIINP-O was significantly raised in the group of MTX-treated psoriatics (P < 0.001). Within this group, levels were significantly higher in patients with inflammation, fibrosis or cirrhosis compared with those with normal histology or steatosis alone (P < 0.0001). In contrast, PIIINP-B and LamP1-B did not distinguish between controls and MTX-treated patients or between histological groups. Forty-two patients had two or more biopsies with simultaneous PIIINP-O measurement. PIIINP-O levels at the time of the first biopsy were normal in six of the seven patients whose histology was initially normal and subsequently became abnormal. A single measurement of PIIINP-O thus did not predict which patients might develop abnormal histology following further MTX. In a group of 17 patients, PIIINP-O was measured 3-monthly for up to 6 years during MTX treatment. PIIINP-O was elevated at some time during follow-up in all three patients who developed abnormal histology but was consistently normal in eight of the 11 patients whose histology remained or became normal. Our findings indicate that PIIINP-O is of value in detecting liver damage and, particularly if measured serially, may reduce the need for liver biopsy in MTX-treated patients. Although the test does not detect all patients with fibrosis, it would appear that the risk of missing significant liver damage in patients with persistently normal PIIINP-O is low.
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Kon OM, Redhead JB, Gillen D, Fothergill J, Henry JA, Mitchell DM. "Crack lung" caused by an impure preparation. Thorax 1996; 51:959-60. [PMID: 8984712 PMCID: PMC472624 DOI: 10.1136/thx.51.9.959] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/03/2023]
Abstract
Pulmonary complications of crack cocaine have been reported mainly from American centres. Crack usage is now on the increase in the UK. Three cases of "crack lung" are reported in patients who acquired the drug from the same source. The pulmonary syndrome they developed was due to an impure form of crack.
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Hosler JP, Shapleigh JP, Mitchell DM, Kim Y, Pressler MA, Georgiou C, Babcock GT, Alben JO, Ferguson-Miller S, Gennis RB. Polar residues in helix VIII of subunit I of cytochrome c oxidase influence the activity and the structure of the active site. Biochemistry 1996; 35:10776-83. [PMID: 8718868 DOI: 10.1021/bi9606511] [Citation(s) in RCA: 74] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/01/2023]
Abstract
The aa3-type cytochrome c oxidase from Rhodobacter sphaeroides is closely related to eukaryotic cytochrome c oxidases. Analysis of site-directed mutants identified the ligands of heme a, heme a3, and CuB [Hosler et al. (1993) J. Bioenerg. Biomembr. 25, 121-133], which have been confirmed by high-resolution structures of homologous oxidases [Iwata et al. (1995) Nature 376, 660; Tsukihara et al. (1995) Science 269, 1069; (1996) 272, 1136]. Since the protons used to form water originate from the inner side of the membrane, and the heme a3-CuB center is located near the outer surface, the protein must convey these substrate protons to the oxygen reduction site. Transmembrane helix VIII in subunit I is close to this site and contains several conserved polar residues that could function in a rate-determining proton relay system. To test this role, apolar residues were substituted for T352, T359, and K362 in helix VIII and the mutants were characterized in terms of activity and structure. Mutation of T352, near CuB, strongly decreases enzyme activity and disrupts the spectral properties of the heme a3-CuB center. Mutation of T359, below heme a3, substantially reduces oxidase activity with only minor effects on metal center structure. Two mutations of K362, approximately 15 A below the axial ligand of heme a3, are inactive, make heme a3 difficult to reduce, and cause changes in the resonance Raman signal specific for the iron-histidine bond to heme a3. The results are consistent with a key role for T352, T359, and K362 in oxidase activity and with the involvement of T359 and K362 in proton transfer through a relay system now plausibly identified in the crystal structure. However, the characteristics of the K362 mutants raise some questions about the assignment of this as the substrate proton channel.
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Mitchell DM, Shapleigh JP, Archer AM, Alben JO, Gennis RB. A pH-dependent polarity change at the binuclear center of reduced cytochrome c oxidase detected by FTIR difference spectroscopy of the CO adduct. Biochemistry 1996; 35:9446-50. [PMID: 8755723 DOI: 10.1021/bi960392f] [Citation(s) in RCA: 27] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/02/2023]
Abstract
A pH-dependent polarity change at the heme-copper binuclear center of the aa3-type cytochrome c oxidase from Rhodobacter sphaeroides has been identified by low-temperature FTIR difference spectroscopy. "Light"-minus-"dark" FTIR difference spectra of the fully reduced CO-enzyme adduct were recorded at a range of pH, and the dominance of different populations of bound CO, alpha and beta, was found to vary with pH. An apparent pKa of about 7.3 for the transition was obtained. The alpha and beta forms are differentiated by different polarities at the heme-copper binuclear center of the enzyme, sensed by the stretching frequencies of CO bound either to the heme alpha 3 Fe or to CuB. Several site-directed mutants in the vicinity of the heme-copper center are shown to favor either the alpha or the beta forms of the enyzme, suggesting that what is being monitored is an equilibrium between two conformations of the reduced form of the oxidase. Recent resonance Raman evidence has been presented demonstrating that the alpha and beta forms of the R. sphaeroides oxidase exist at room temperature; therefore, the pH-dependent change in the polarity in the vicinity of the heme-copper center may be functionally significant.
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Mitchell DM, Clarke JR. The lung in HIV infection: can pulmonary function testing help? Monaldi Arch Chest Dis 1996; 51:214-22. [PMID: 8766197] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/02/2023] Open
Abstract
Simple lung function tests have been used to evaluate respiratory symptoms in human immunodeficiency virus (HIV) infected individuals. Abnormalities of simple lung function tests, in particular decreases in the transfer factor of the lung for carbon monoxide (TL,CO) have been described in patients with acquired immune deficiency syndrome (AIDS) who have respiratory disease. Early studies showed marked reductions in TL,CO in patients with pneumocystis pneumonia but other forms of pulmonary infection or neoplasm also resulted in reductions in TL,CO values. Lung function studies in larger numbers of patients have shown reductions in all lung function measurements, particularly in TL,CO. in all categories of HIV disease. The most marked reductions in TL,CO are seen in patients with pneumocystis pneumonia but reductions also occur in pulmonary bacterial infection, tuberculosis and pulmonary Kaposi's sarcoma. TL,CO values improved following recovery from pneumocystis pneumonia but rarely returned to normal. Zidovudine therapy does not contribute to the abnormalities of lung function but smokers generally have worse lung function tests in all categories of HIV disease. The diagnostic usefulness of simple lung function tests is limited. A reduced TL,CO is a highly sensitive index for the presence of pneumonitis (pneumocystis or otherwise) in HIV-infected individuals but lacks the necessary specificity to be a satisfactory diagnostic tool. Simple lung function tests have limitations but have a value as a simple screening test to determine the presence of underlying organic disease in HIV seropositive patients with respiratory symptoms. The presence of a normal TL,CO value makes the presence of pneumonitis unlikely.
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Jones CM, Lake RA, Wijeyekoon JB, Mitchell DM, du Bois RM, O'Hehir RE. Oligoclonal V gene usage by T lymphocytes in bronchoalveolar lavage fluid from sarcoidosis patients. Am J Respir Cell Mol Biol 1996; 14:470-7. [PMID: 8624252 DOI: 10.1165/ajrcmb.14.5.8624252] [Citation(s) in RCA: 17] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/31/2023] Open
Abstract
The T-cell antigen receptor (TCR) repertoire was examined in lymphocytes isolated from the lungs and blood of 12 sarcoidosis patients and nine control patients. This analysis, by polymerase chain reaction (PCR), examined the variable (V)-domain genes of both the alpha and beta chains of the TCR. This is the first study to examine the usage of all known V alpha gene segments in sarcoidosis. A similar degree of diversity was observed in the TCR repertoire in the lungs and blood of the sarcoidosis patients. However, 11 of the 12 sarcoidosis patients showed an increased use of particular TCR V alpha and V beta genes in lung T cells as compared with blood. The pattern of TCR V gene bias in the lung T cells was specific for each patient. The clonality of selected V genes was examined by determining the third complementarity-determining region (CDR3) length polymorphism of particular PCR products. The majority of lung T cells with biased TCR V gene segments were oligoclonal. Altogether, these results suggest oligoclonal expansion of lung T cells in response to a local antigenic stimulus, with additional nonspecific T-cell accumulation. The variability in the V gene segments used by the expanded T-cell subsets in different sarcoidosis patients may reflect different epitopes or antigens being recognized in the lung, as well as variations in major histocompatibility complex (MHC) haplotype between the patients.
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Mitchell DM, Adelroth P, Hosler JP, Fetter JR, Brzezinski P, Pressler MA, Aasa R, Malmström BG, Alben JO, Babcock GT, Gennis RB, Ferguson-Miller S. A ligand-exchange mechanism of proton pumping involving tyrosine-422 of subunit I of cytochrome oxidase is ruled out. Biochemistry 1996; 35:824-8. [PMID: 8547262 DOI: 10.1021/bi951897t] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/31/2023]
Abstract
The molecular mechanism by which proton pumping is coupled to electron transfer in cytochrome c oxidase has not yet been determined. However, several models of this process have been proposed which are based on changes occurring in the vicinity of the redox centers of the enzyme. Recently, a model was described in which a well-conserved tyrosine residue in subunit I (Y422) was proposed to undergo ligand exchange with the histidine ligand (H419) of the high-spin heme a3 during the catalytic cycle, allowing both residues to serve as part of a proton transporting system. Site-directed mutants of Y422 have been constructed in the aa3-type cytochrome c oxidase of Rhodobacter sphaeroides to test this hypothesis (Y422A, Y422F). The results demonstrate that Y422 is not an essential residue in the electron transfer and proton pumping mechanisms of cytochrome c oxidase. However, the results support the predicted proximity of Y422 to heme a3, as now confirmed by crystal structure. In addition, it is shown that the pH-dependent reversed electron transfer between heme a and heme a3 is normal in the Y422F mutant. Hence, these data also demonstrate that Y422 is not the residue previously postulated to interact electrostatically with heme a3, nor is it responsible for the unique EPR characteristics of heme a in this bacterial oxidase.
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Taylor IK, Coker RJ, Clarke J, Moss FM, Nieman R, Evans DJ, Veale D, Shaw RJ, Robinson DS, Mitchell DM. Pulmonary complications of HIV disease: 10 year retrospective evaluation of yields from bronchoalveolar lavage, 1983-93. Thorax 1995; 50:1240-5. [PMID: 8553294 PMCID: PMC1021344 DOI: 10.1136/thx.50.12.1240] [Citation(s) in RCA: 23] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/31/2023]
Abstract
BACKGROUND Pulmonary disease is a major contributor to morbidity and mortality in patients with HIV infection and AIDS. The aim of this study was to describe bronchoscopic findings and the spectrum of pulmonary pathogens in HIV seropositive patients undergoing investigation of respiratory disease over a 10 year period in a major UK referral centre. METHODS Recruitment was procedure based with data being captured when bronchoscopy was clinically indicated. Data were evaluated from 580 HIV seropositive patients (559 men, age 13-65 years) over a 10 year period from June 1983 to March 1993. RESULTS A total of 947 bronchoscopies was performed. The most frequent pulmonary pathogen isolated from bronchoalveolar lavage (BAL) fluid in 44% of all bronchoscopies was Pneumocystis carinii. Of all patients studied, 324 (55%) had at least one cytologically confirmed episode of P carinii pneumonia; this was AIDS defining in 219 (38%) of patients who underwent bronchoscopy. Between 1987 and 1993 the overall diagnostic yield from BAL fluid was 76%; 25% of all bronchoscopies yielded positive microbiological results, the most frequent isolates being Staphylococcus aureus, Streptococcus pneumoniae, Pseudomonas spp, and Haemophilus influenzae. Mycobacteria were identified in 8% of patients; M tuberculosis was the most common being identified in 3% of lavage samples and in 4% of patients. No drug-resistant M tuberculosis was found. Viral isolates (mainly cytomegalovirus) were identified in up to 31% of BAL fluid samples. Endobronchial Kaposi's sarcoma was seen in 15% of patients at bronchoscopy. CONCLUSIONS Of the 1956 newly diagnosed HIV seropositive patients receiving clinical care at St Mary's Hospital over this period, approximately 30% underwent bronchoscopy. Diagnostic rates for P carinii pneumonia, endobronchial Kaposi's sarcoma, and bacterial and mycobacterial infection have remained largely constant since 1989. Bronchoalveolar lavage produces high diagnostic yields generally, and P carinii pneumonia remains a common cause of pulmonary disease in these patients.
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Mitchell DM, Aasa R, Adelroth P, Brzezinski P, Gennis RB, Malmström BG. EPR studies of wild-type and several mutants of cytochrome c oxidase from Rhodobacter sphaeroides: Glu286 is not a bridging ligand in the cytochrome a3-CuB center. FEBS Lett 1995; 374:371-4. [PMID: 7589573 DOI: 10.1016/0014-5793(95)01149-9] [Citation(s) in RCA: 21] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/26/2023]
Abstract
Wild-type and several mutants of cytochrome c oxidase from Rhodobacter sphaeroides were characterized by EPR spectroscopy. A pH-induced g12 signal, seen previously in mammalian cytochrome oxidase and assigned to the presence of a bridging carboxyl ligand in the bimetallic cytochrome a3-CuB site, is found also in the bacterial enzyme. Mutation of glutamate-286 to glutamine inactivates the enzyme but does not affect this signal, demonstrating that the carboxyl group of this residue is not the bridging ligand. Three mutants, M106Q, located one helix turn below a histidine ligand to cytochrome a, and T352A as well as F391Q, located close to the bimetallic center, are shown to affect dramatically the low-spin heme signal of cytochrome a. These mutants are essentially inactive, suggesting that these three mutations result in alterations to cytochrome a that render the oxidase non-functional.
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Boffa MJ, Chalmers RJ, Haboubi NY, Shomaf M, Mitchell DM. Sequential liver biopsies during long-term methotrexate treatment for psoriasis: a reappraisal. Br J Dermatol 1995; 133:774-8. [PMID: 8555032 DOI: 10.1111/j.1365-2133.1995.tb02754.x] [Citation(s) in RCA: 77] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/31/2023]
Abstract
One hundred and eighty-two liver biopsies were performed over a 10-year period on patients receiving long-term, low-dose, once weekly oral methotrexate (MTX) for severe psoriasis. Forty-nine patients had two or more biopsies during continued treatment and formed the study population for our analysis. The first and last biopsies were compared to determine progression of any histological abnormalities. Liver biopsies were assessed without knowledge of the MTX dose and allocated to one of five groups according to the severity of the histological abnormalities. These were defined as: (1) normal; (2) steatosis alone; (3) inflammation without fibrosis; (4) fibrosis; and (5) cirrhosis. The mean cumulative dose of MTX at the time of the first biopsy was 2743 mg (range 315-10,024), given over 275 weeks (range 26-738). In the interval between the first and last biopsies, patients received, on average, a further 2362 mg (range 390-7155) over 225 weeks (range 60-460). There was improvement in the histological assessment in 12 patients, no change in 28 patients, and deterioration in nine patients. None developed cirrhosis. Liver biopsy findings prompted discontinuation of MTX in four of the 49 patients on long-term treatment. This has to be weighed against the cost and morbidity of the 124 biopsies performed in these patients. Our results suggest that, with careful follow-up, the risk of development or progression of liver disease in patients receiving long-term, low-dose, once weekly oral MTX for psoriasis is modest, and that the requirement for performing routine liver biopsies in these patients needs to be reconsidered.
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