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Biomedical subjects

M Boehm

Publications and source records attributed to M Boehm.

27 records · Page 2Linked to original sources
PubMed1996

Cloning, high-yield expression in Escherichia coli, and purification of biologically active HIV-1 Tat protein.

We have established an expression system for full-length HIV-1 transactivator (Tat) protein in Escherichia coli. By constructing a synthetic gene for high level expression in enteric bacteria, the recombinant protein can be obtained in high yield. Fusion of the Tat sequence to an N-terminal histidine tag allows the rapid purification of the fusion protein through a single chromatographic step. After cleavage of the fusion protein with CNBr, pure Tat can be obtained through the use of a MonoS column. Reduction of the protein with Tris(2-carboxyethyl)phosphine-HCl and subsequent stepwise refolding yields biologically active Tat. Sample purity and the identity of the protein mass with the mass expected from the amino acid sequence was demonstrated by mass spectrometry. Nuclear magnetic resonance spectroscopy showed the identity of bacterially expressed and chemically synthesized Tat protein (P. Bayer et al., 1995, J. Mol. Biol. 247, 529-535). The expression of Tat in E. coli enables isotope labeling as a prerequisite for multidimensional NMR experiments toward the elucidation of the structure of the Tat-trans-activation response element complex.

Amino Acid Sequence↗
PubMed1994

Regulation of retinoid signalling by receptor polarity and allosteric control of ligand binding.

Retinoic acid receptors (RARs) and retinoid X receptors (RXRs) regulate transcription by binding to response elements in target genes that generally consist of two direct repeat half-sites of consensus sequence AGGTCA (ref. 1). RAR/RXR heterodimers activate transcription in response to all-trans or 9-cis retinoic acid by binding to direct repeats spaced by five base pairs (DR5 elements), such that RAR occupies the downstream half-site. RXR homodimers activate transcription in response to 9-cis retinoic acid by binding to direct repeats spaced by one base pair (DR1 elements). Although RXR/RAR heterodimers bind to DR1 elements with higher affinity than RXR homodimers, in most contexts they are unable to activate transcription in response to either all-trans or 9-cis retinoic acid. As a result, RARs inhibit RXR-dependent transcription from these sites. We report that the switching of the RAR from an activator to an inhibitor of retinoid-dependent transcription requires that it be bound to the upstream half-site of DR1 elements and that it allosterically block the binding of ligand to the RXR.

Allosteric Regulation↗
PubMed1989

A multicenter trial of interleukin-2 and low-dose cyclophosphamide in highly chemotherapy-resistant malignancies.

The anti-tumor activity of high-dose recombinant interleukin-2 (IL-2) has been demonstrated in several recent preclinical and clinical studies. In an attempt to study possible synergistic effects with low-dose cyclophosphamide (CYC), a phase II clinical trial was initiated in 32 patients, 18 with malignant melanoma (MM) and 14 with renal cell carcinoma (RCC). The recombinant IL-2 (Cetus Corp., Emeryville, Ca, U.S.A.) was given once daily at 3 x 10(6) U/m2, as a 30-min infusion for 14 days in cycle I and for five days twice in cycles II and III, respectively; if tolerated, the dose was escalated to a maximum of 6 x 10(6) U/m2/day; the cycles, separated by 1-week treatment-free intervals, were each preceded by a single i.v. bolus of CYC at 350 mg/m2. The most prominent side-effects encountered in this trial consisted of a capillary leak syndrome, myalgia and fever requiring dose reduction in half of the patients during the first cycle. Given the limit of tolerable toxicities in a standard care unit, the regimen employed achieved minor anti-tumor activity. No objective responses were achieved in patients with RCC and a 15% remission rate (PR + MR) was seen in melanoma patients.

Antineoplastic Combined Chemotherapy Protocols↗
PubMed1985

Renal perfusion and mean vascular transit time.

A method was developed to determine the mean vascular (arterio-venous) transit time (MVTT) of renal transplants. The renal transit times were calculated from perfusion curves obtained when grafts were examined with 99mTc-DTPA. About 400 examinations were performed during a 6-month period. As a result, influences of clinical complications on transit times were demonstrated. It was found that the individual MVTT is not a suitable parameter for assessment of renal grafts since individual transit times vary widely.

Graft Rejection↗
PubMed1985

Estimating the effective renal plasma flow from the hippurate renogram.

A method for estimating the effective renal plasma flow (ERPF) from renograms is presented. Renograms obtained in 91 patients were used to test the method. The clearance values derived from renography were compared with those obtained with infusion clearance. It was shown that the ERPF was able to be estimated from the renogram with a standard error of +/- 94 ml min-1.

Glomerular Filtration Rate↗
PubMed1982

Immunoinhibition and automated column chromatography compared for assay of creatine kinase isoenzyme MB in serum.

We examined sera from six different groups of patients for CK-MB activity by means of two commercially available tests, an immunoinhibition method (E. Merck) and the CK-MB test as used with the aca (Du Pont). In the first group of patients (suspicion of myocardial infarction) the correlation between the two methods was good: r = 0.9191, y = 1.068x -- 0.888, x = 18.7 U/L, y = 19.0 U/L. In the second group, patients with high adenylate kinase activity, no interference was detectable on the aca, whereas the immunoinhibition method yielded falsely high CK-MB values. The third group consisted of persons with macro-CK-BB in their serum. In the immunoinhibition test these patients usually showed a high CK-MB:total CK ratio, whereas such results were rarely found for the aca. The fourth group, patients with a different electrophoretic mobility of their CK-isoenzymes (migration of an active band towards the cathode), were detected by the immunoinhibition method (high ratio of CK-MB to total CK), but not with the aca. In the presence of free CK-BB (group five) the immunoinhibition test resulted in "falsely" high CK-MB values, whereas CK-BB was retained on the column of the aca. In skeletal muscle diseases (group six) results by the two methods differed, values for CK-MB on the aca being much higher. It was demonstrated experimentally that this was due to CK-MM with altered surface charge.

Adenylate Kinase↗
PubMed1977

Susceptibility to erythromycin of anaerobes of the genera Bacteroides, Fusobacterium, Sphaerophorus, Veillonella, Clostridium, Corynebacterium, Peptococcus, Peptostreptococcus.

The minimal inhibitory concentrations (MIC) of erythromycin were determined by broth dilution tests for 313 anaerobic strains, most of which were clinical isolates. All the gram-positive anaerobes tested (84 Peptococcaceae, including 21 Peptostreptococcus anaerobius and 15 Peptococcus variabilis; 65 Corynebacterium acnes and 29 Clostridium strains, including 13 C. perfringens) were sensitive (MIC values 0.012 through 3.12 microgram erythromycin/ml); so were 111 cultures of gram-negative anaerobes (52 Bacteroides fragilis, 12 B. thetaiotaomicron, 7 B. vulgatus, 13 B. oralis, 4 B. melaninogenicus, 10 Sphaerophorus necrophorus, 2 Veillonella sp., 11 members of other species). Erythromycin at concentrations of 6.25 through 200.0 microgram/ml was active against 24 strains (1 B. fragilis, 4 Fusobacterium fusiforme, 9 Sph. freundi, 10 Sph. varius). The present results are compared to the limited number of reports existing with regard to the susceptibility of anaerobes to erythromycin.

Bacteroides↗
PubMed1976

[Life threatening infection with bacteroides fragilis in connection with Dalkon shield (author's transl)].

A case of severe peritonitis in connection with the application of a Dalkon Shield is reported. By culturing the peritoneal exsudate a monoculture of Bacteroides fragilis was found as causing agens. The general aspects of severe infection in connection with IUD, particularly the Dalkon Shield, are discussed. By analysing the reports in the literature it cannot be ruled out, that Bacteroides fragilis may to be a major factor in cases with lethal outcome.

Adult↗