Fast-scan cyclic voltammetry of protein films on pyrolytic graphite edge electrodes: characteristics of electron exchange

The rapid electron-exchange characteristics of metalloproteins adsorbed at a pyrolytic graphite "edge" electrode have been studied by analog dc cyclic voltammetry at scan rates up to 3000 V s-1. The voltammetry of four proteins, azurin (a "blue" copper protein) and three 7Fe ferredoxins, reveals oxidation and reduction peaks that display only modest increases in width and peak separation as the scan rate is raised. This is indicative of a substantially homogeneous population of noninteracting centers which undergo rapid electron exchange with the electrode. Both the Butler--Volmer and Marcus models have been tested. The electrochemical kinetics, as reflected by k0 (the rate at zero overpotential), are too fast to allow the determination of reorganization energies by this method. Nonetheless, the rapid and energetically coherent nature of the electron transfer enables the cyclic oxidation and reduction of protein redox centers to be examined on a time scale sufficiently short to recognize coupled processes occurring in the millisecond time domain, which are characteristic of the protein under investigation. Two of the ferredoxins display increasingly asymmetric voltammetry as the scan rate is increased, which is attributed to the coupling of electron transfer to conformational (or orientational) changes. For azurin, the use of higher electrolyte concentrations enables studies to be made at scan rates up to 3000 V s-1, from which a standard electron-transfer rate constant in the region of 5000 s-1 is obtained. At these high scan rates, azurin still shows very symmetrical voltammograms but with peak shapes displaying a more gradual decrease in current, at increasing overpotential, than is predicted using realistic values of the reorganization energy. The ability to measure even faster rate constants and access coupled reactions occurring in shorter time domains is likely to be limited by complex processes occurring on the graphite surface.     

Ductal carcinoma in situ: introduction of the concept of ductal intraepithelial neoplasia

The current definition, diagnostic criteria, grading, and approach to assessment of extent of ductal carcinoma in situ (DCIS) are presented. The problem areas, particularly the difficulties in separating low-grade DCIS from atypical intraductal hyperplasia (AIDH), accurate assessment of size and/or extent of DCIS, and their impact on patient management are critically reviewed. On the basis of the route of progression of DCIS, recently confirmed by three-dimensional reconstructed models, an optimal and simple approach to uniform excision, orientation, and processing of biopsy samples is presented. Emphasis is placed on the role of intraductal proliferative lesions (IDH, AIDH, and DCIS) as risk factors of variable magnitude in subsequent development of invasive breast carcinoma. It is proposed that these proliferations should be classified as "mammary intraepithelial neoplasia, ductal type" or as "ductal intraepithelial neoplasia" (DIN); the rational for the application of this classification system is provided. This approach obviates the current separation of AIDH and low-grade DCIS into two very drastically different categories of cancer and non-cancer without interfering with appropriate management of the various lesions. The DIN classification is presented in a simple translational table, along with the current terminology for various lesions.     

The morphology and pathology of Besnoitia sp. in reindeer (Rangifer tarandus tarandus)

In this prospective study the authors analysed the prognostic value of monitoring patency of the feedings vessels of the fibular graft, implanted into the femoral head to treat aseptic necrosis. In 26 patients (29 hips) we applied a three phase 99Tc-MDP Bone Scanning in the seventh postoperative day. One week later; 18 patients had a digital subtraction angiography of the lateral femoral circumflex artery and its branches. The patients were followed for average time of 22 months. The average Harris Hip Score of the affected hips improved clinically from 69.5 to 93.5. The vessels were patent prior to the wound closure. Phase I of the bone scan served as "radionuclide angiogram" and demonstrated patent vessels in all about three hips. The digital arteriograms demonstrated patent anastomotic sites in 15 out of 18 hips. Only in four of the fifteen arteriograms the vessels were visualized throughout the length of the graft. Two of the three hips with negative arteriograms have also had negative bone scans, both in patients with haemoglobinopathies. None of the patients required further surgery because of failure of the procedure. This study demonstrated that the phase I of the bone scan at the end of the first week postoperatively is very sensitive means for monitoring the viability of the graft. Digital arteriograms although more specific, were less sensitive. Early postoperative monitoring of the graft viability maintained high predictive value for the outcome of the treatment in the medium-term.     

Prevention of murine collagen-induced arthritis in the knee and ipsilateral paw by local expression of human interleukin-1 receptor antagonist protein in the knee

OBJECTIVE: To determine the efficacy of local human interleukin-1 receptor antagonist (HuIL-1Ra) gene therapy in murine collagen-induced arthritis (CIA). METHODS: DBA/1 mice were immunized against bovine type II collagen. Before the onset of arthritis, NIH/3T3 fibroblasts transfected with pMFG-IRAP were transplanted into the knee cavity. Normal NIH/3T3 cells served as controls. Paws were evaluated macroscopically for redness, swelling, and deformities during the course of arthritis. Swelling of the knee joints was measured by external gamma counting of 99mtechnetium accumulation in the joint. Paws and knee joints were dissected and processed for histologic studies to evaluate inflammation and cartilage destruction. RESULTS: The NIH/3T3 fibroblasts survived in the joint cavity of DBA mice for at least 7 days. The transduced cells expressed immunoreactive and bioactive HuIL-1Ra in the knee joint, and produced sufficient amounts to block the effect of 1 ng of recombinant murine IL-1alpha on chondrocyte proteoglycan synthesis. The onset of CIA was almost completely prevented in knee joints containing HuIL-1Ra-producing cells, whereas joints containing normal cells showed severe inflammation and destruction of cartilage. Moreover, onset of CIA in the draining joints (ipsilateral paws) of the HuIL-1Ra gene-bearing knees was also prevented. CONCLUSION: Local production of HuIL-1Ra in the knee was able to ameliorate the effects of IL-1 on cartilage and could prevent the onset of CIA not only in that knee, but also in the "draining" paw. This indicates the feasibility of gene transfer as a therapeutic approach to modulating arthritis.     

Time-resolved resonance Raman study on the binding of carbon monoxide to recombinant human myoglobin and its distal histidine mutants

Time-resolved resonance Raman (RR) spectra of the recombined species of photodissociated CO with recombinant human myoglobin (Mb) and several E7 mutants, in which distal His was replaced by Gly (H64G), Gln (H64Q), Ala (H64A), Ile (H64I), Val (H64V), and Leu (H64L) through site-directed mutagenesis, were observed in the time range -20 ns to 1 ms following photolysis. The Fe-CO stretching (VFe-CO) RR band was observed successfully with pulse excitation when the laser power was greatly reduced. H64H, H64G, and H64Q gave the VFe-CO band at 505-510 cm-1 in their stationary states. In their recovery processes 1-100 microseconds after photodissociation, a broad transient band was observed at slightly lower frequencies than those of their equilibrium structures for H64G and H64Q, but a transient VFe-CO band corresponding to the so-called "open" form was not identified around 490 cm-1 for any of the three species. A second group, H64A, H64I, H64V, and H64L, gave the main VFe-CO band at 490-495 cm-1 with a shoulder around 510 cm-1 (except for H64L) in the stationary state and exhibited a much faster recovery than the first group. These latter four species gave a broad transient band around 492-500 cm-1 in the time range of 100-1000 ns, while the approximately 510 cm-1 shoulder appeared much later. The equilibrium relative intensity of the two bands was attained at 500 microseconds, suggesting that the interconversion between the two forms is slower than 100 microseconds.(ABSTRACT TRUNCATED AT 250 WORDS)     

Leucine/isoleucine/valine-binding protein contracts upon binding of ligand

Small-angle x-ray scattering and computer modeling have been used to study the effects of ligand binding to the leucine/isoleucine/valine-binding protein, an initial component of the high-affinity active transport system for branched-chain aliphatic amino acids in Escherichia coli. Measurements were made with no ligand present and with either L-leucine or L-valine present. Upon binding of either leucine or valine, there is a decrease in the radius of gyration, from 23.2 +/- 0.2 to 22.2 +/- 0.2 A, and in the maximum particle dimension, from 82 +/- 3 to 73 +/- 3 A. The x-ray structure of the unbound form has been determined and gives a radius of gyration and a maximum dimension consistent with the values found for the solution structure in this study (Sack, J. S., Saper, M. A., and Quiocho, F. A. (1989) J. Mol. Biol. 206, 171-191). The reduction in the radius of gyration and maximum dimension upon ligand binding can be accounted for by a substrate-induced cleft closure in a combined "hinge-twist" motion. Modeling of the substrate-bound state was done by comparison of this protein with another periplasmic binding protein (L-arabinose-binding protein), which possesses a similar two-lobe structure and for which the x-ray structure is known in its ligand-bound form.     

Estimating in situ exposure in the presence of acoustic nonlinearity

Evidence is presented for excess attenuation of pulsed ultrasound due to finite amplitude effects in water. Measurements on a modern scanner are used to demonstrate that linear derating can underestimate many exposure quantities, including all safety indices apart from the cranial thermal index. More appropriate methods for estimating in situ exposure are reviewed. A preferred procedure that requires exposure measurements to be made in water under "small signal" conditions is selected. A spectral index is defined that is proposed as an indicator of finite amplitude effects, where spectral index = 0.1 defines the threshold between nonlinear and quasi-linear conditions.     

水煤气净化系统氨积累处理方法

对水煤气净化系统氨积累成因进行分析,由于流体流动边界层的存在,氨与部分冷凝水在换热器管程内壁反应形成盐溶液并在管程内冷却结晶,从而造成铵盐结晶.从能量利用和水的平衡进行分析,提出改进措施,为合成氨装置技改提供参考.     

Glass formation and magnetic properties of Fe-based metallic glasses fabricated by low-purity industrial materials

Fe-based metallic glasses of (Fe₇₄Nb₆B₂₀)_100-xCr_x (x=1, 3, 5) with high glass forming ability (GFA) and good magnetic properties were prepared using low-purity raw materials. Increasing Cr content does not significantly change glass transition temperature and onset crystallization temperature, while it enhances liquidus temperature. The addition of Cr improves the GFA of the (Fe₇₄Nb₆B₂₀)_100-xCr_x glassy alloys compared to that in Cr-free Fe-Nb-B alloys, in which the supercooled liquid region (ΔT_x), T_rg and γ are found to be 50–54 K, 0.526–0.538, and 0.367–0.371, respectively. The (Fe₇₄Nb₆B₂₀)_100–xCr_x glassy alloys exhibit excellent soft magnetic properties with high saturation magnetization of 139–161 A·m²/kg and low coercivity of 30.24–58.9 A/m. Present Fe-Nb-B-Cr glassy alloys exhibiting high GFA as well as excellent magnetic properties and low manufacturing cost make them suitable for magnetic components for engineering application.