Biomedical subjects
Publications and source records attributed to A Chapman.
In an audit of a protocol for the follow-up of patients treated for hypertension, it was found that satisfactory compliance to standards was met for the majority. Satisfactory results are dependent on having one person responsible for follow-up and record systems.
Since 1970, the types of glomerulopathy encountered in patients with cirrhosis of the liver have been accurately determined. In alcoholic cirrhosis IgA glomerulonephritis is frequent, usually non-proliferative and latent, sometimes membranoproliferative. Defective elimination of circulating immune complexes made up of bacterial or food antigens and IgA antibodies is thought to play a part in the pathogenesis of this type of glomerulonephritis. Extramembranous or membranoproliferative glomerulonephritis, occasionally containing the viral antigen, may complicate post-hepatitis cirrhosis, in which case an antiviral treatment might be effective against the renal disease.
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A ferredoxin has been isolated from the thermophilic methanogen Methanococcus thermolithotrophicus. The native protein was a monomer exhibiting a molecular weight of 7,262, calculated from the amino acid composition. Its absorption spectrum had two maxima at 390 and 283 nm, with an absorbance ratio A390/A283 of 0.79. The absorption at 390 nm (E = 29 mM-1 cm-1) and the content of iron of the protein are in agreement with the presence of two 4Fe-4S clusters in M. thermolithotrophicus ferredoxin. Its amino acid composition showed the presence of eight cysteine residues, which is the required number of cysteines for the binding of two 4Fe-4S clusters. The protein was characterized by the lack of histidine, arginine, and leucine and a high content of valine. It was unusually stable to high temperatures but not to oxygen. The ESR spectrum of the protein in the oxidized state showed a minor signal at g = 2.01, corresponding to an oxidized 3Fe-4S cluster. The protein, which was difficult to reduce with dithionite or reduced mediators, exhibited in its reduced state a spectrum typical of two interacting reduced 4Fe-4S clusters. M. thermolithotrophicus ferredoxin functioned as an electron acceptor for the CO dehydrogenase complex with an extract free of ferredoxin. No reaction was detected with F420 or hydrogenase.
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The nickel centre of hydrogenase from Desulfovibrio gigas was studied by electron spin echo envelope modulation (ESEEM) spectroscopy in the oxidized, unready (Ni-A) and H2-reduced active (Ni-C) states, both in H2O and 2H2O solutions. Fourier transforms of the 3-pulse ESEEM, taken at 8.7 GHz, for Ni-A and Ni-C in H2O contained similar peaks with narrow linewidths at frequencies of 0.4, 1.2 and 1.6 MHz, and a broader peak centered at 4.5 MHz. At 11.6 GHz, the low frequency components showed small field-dependent shifts, while the high frequency component was shifted to 5.1 MHz. These results are consistent with the presence of 14N, possibly from imidazole, coupled to the nickel centre. In 2H2O, Ni-A was shown to be inaccessible for exchange with solvent deuterons. In contrast, Ni-C was accessible to solvent exchange, with a deuterium population being in close proximity to the metal ion. Thus, the nickel environment of the active protein is different from that in the oxidized or unready state. On illumination of Ni-C, although EPR changes are seen, 14N coupling remains, and for the 2H2O sample, deuterium coupling is also retained.
(1) The reaction of the resting form of oxidised cytochrome c oxidase from ox heart with dithionite has been studied in the presence and absence of cyanide. In both cases, cytochrome a reduction in 0.1 M phosphate (pH 7) occurs at a rate of 8.2.10(4) M-1.s-1. In the absence of cyanide, ferrocytochrome a3 appears at a rate (kobs) of 0.016 s-1. Ferricytochrome a3 maintains its 418 nm Soret maximum until reduced. The rate of a3 reduction is independent of dithionite concentration over a range 0.9 mM-131 mM. In the presence or cyanide, visible and EPR spectral changes indicate the formation of a ferric a3/cyanide complex occurs at the same rate as a3 reduction in the absence of cyanide. A g = 3.6 signal appears at the same time as the decay of a g = 6 signal. No EPR signals which could be attributed to copper in any significant amounts could be detected after dithionite addition, either in the presence or absence of cyanide. (2) Addition of dithionite to cytochrome oxidase at various times following induction of turnover with ascorbate/TMPD, results in a biphasic reduction of cytochrome a3 with an increasing proportion of the fast phase of reduction occurring after longer turnover times. At the same time, the predominant steady state species of ferri-cytochrome a3 shifts from high to low spin and the steady-state level of reduction of cytochrome a drops indicating a shift in population of the enzyme molecules to a species with fast turnover. In the final activated form, oxygen is not required for fast internal electron transfer to cytochrome a3. In addition, oxygen does not induce further electron uptake in samples of resting cytochrome oxidase reduced under anaerobic conditions in the presence of cyanide. Both findings are contrary to predictions of certain O-loop types of mechanism for proton translocation. (3) A measurement of electron entry into the resting form of cytochrome oxidase in the presence of cyanide, using TMPD or cytochrome c under anaerobic conditions, shows that three electrons per oxidase enter below a redox potential of around +200 mV. An initial fast entry of two electrons is followed by a slow (kobs approximately 0.02 s) entry of a third electron.(ABSTRACT TRUNCATED AT 400 WORDS)
Electron spin-echo envelope modulation (ESEEM) spectroscopy was applied to the study of reduced Centre 1 of Escherichia coli fumarate reductase (succinate:(acceptor) oxidoreductase, EC 1.3.99.1). The ESEEM spectrum derived from stimulated (3-pulse) echo envelopes obtained at 8.8 GHz contained lines at 0.9, 2.1, 3.0 and 4.2 MHz in the g = 1.94 region. When studied at 11.4 GHz, these low-frequency components scale with magnetic field in a manner indicating interaction between the unpaired electron spin of the Fe-S cluster and a weakly coupled 14N nucleus. Spectral simulations of these ESEEM data yield nuclear quadrupole interaction parameters indicative of peptide nitrogen. For oxidized protein, the magnetic-field dependence of the linear electric-field effect (LEFE) for Centre 3 was measured, and the results confirm the presence of a [3Fe-4S] cluster in the protein.
Several reports have suggested that skin tags may be a marker for the presence of colonic polyps in symptomatic patients referred for colonoscopy. In a prospective study of 100 asymptomatic patients, we found no association between skin tags and colonic polyps. A review of the literature and results of a metaanalysis show a significant association between skin tags and colonic polyps in 777 symptomatic patients, but no association in 268 asymptomatic patients. To explain this discrepancy, several possible biases are analyzed. As skin tags constitute a marker for colonic polyps only in symptomatic patients for whom a colonoscopy is already indicated, their detection is of no diagnostic value in asymptomatic patients.
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Primary manifestations of HIV infection may present as a mononucleosis-like syndrome. Cases have also been reported where it presents with symptoms of encephalitis, meningitis or acute polyneuropathy. When no cause is found for such clinical symptoms, they should suggest the possibility of primary HIV infection even in a patient who is not at risk. HIV antibody will appear in the following weeks and serum studies should be done within the three months that follow. The patient should then be warned that he is contagious. Short term prognostic is usually good. But long term progosis remains uncertain.
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