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Biomedical subjects

J Kuhn

Publications and source records attributed to J Kuhn.

At least 145 records · Page 8Linked to original sources
PubMed1976

Role of D-tryptophan oxidase in D-tryptophan utilization by Escherichia coli.

Mutants of Escherichia coli K-12 that require L-tryptophan (trp) are normally unable to utilize D-tryptophan to fulfill their requirement. However, secondary mutations (dadR) that confer this ability can be isolated. In such strains two distinct enzymes are found to be produced at high levels: D-amino acid oxidase (EC 1.4.3.3) and D-tryptophan oxidase. A convenient assay procedure for D-tryptophan oxidase is described. The two enzymes could be distinguished on the basis of their sensitivity to inhibition by L-phenylalanine and L-tyrosine. Strains that were trp dadR could not grow with D-tryptophan in the presence of L-phenylalanine, but further mutations, Fyo, could be isolated that allowed growth under these conditions. Some of them were characterized by further increases in the level of D-tryptophan oxidase activity and a sharp decrease in D-amino acid oxidase. These kinds of Fyo mutations lay in or near the dadR gene. The substrate specificity of the two enzymes toward a large number of compounds was examined. The transamination of aromatic keto acids was investigated. In the wild-type strain only a single enzyme, transaminase A (EC 2.6.1.5), was found, and it was irreversibly activated when subjected to elevated temperatures. The present state of our knowledge on D-amino acid utilization in E. coli is summarized.

Amino Acid Oxidoreductases↗
PubMed1971

Mutant strains of Escherichia coli K12 that use D-amino acids.

A series of mutations has been isolated that confer upon amino-acid auxotrophs of Escherichia coli K-12 the ability to grow when fed various D-amino acids. Several distinct systems, mediating cellular use of the D-isomers of leucine, histidine, phenylalanine, tyrosine, tryptophan, isoleucine, and valine, can be mutationally activated. Mutations leading to D-tryptophan use (dadR) all map near purB. They result in high activities of an enzyme that deaminates D-amino acids. Neither the enzymes of the tryptophan biosynthetic pathway nor tryptophanase (EC 4.2.1.e) are involved in D-tryptophan utilization.

Amino Acids↗
PubMedDate not supplied

The transcription of bacterial luminescence is regulated by sigma 32.

Luminescence in the marine bacterium, Vibrio fischeri, is regulated by a small molecule, the autoinducer. The transcription of the V. fischeri lux genes also requires a regulatory protein, (luxR), cAMP and CRP. We show that, apart from these components, the transcription of the PR lux operon is also controlled by the activity of sigma 32 (htpR protein). In luminescent Escherichia coli (E. coli/pChv1), as well as in different marine luminous bacteria and their naturally occurring dark (K) variants, the luminescence system can be induced by starvation under microaerophilic conditions. Heat shock also induces luminescence in htpR+ but not in htpR- strains of E. coli/pChv1. An htpR- mutant of E. coli containing pChv1 is very dim and its luminescence is not induced by starvation or heat shock. The addition of a plasmid bearing the gene for htpR+ into such cells restores their response to starvation and heat shock. Cells of wild type E. coli/pChv1 that have been starved or heat shocked respond to lower concentrations of V. fischeri inducer than untreated cells. These cultures also produce more extracellular inducer than untreated cells. Starvation, heat shock and the presence of sigma 32 do not induce luminescence in luxl deleted E. coli/pChv1 cells. SOS-inducing agents advance the onset of luminescence in both htpR+ and htpR- strains but not in luxl deleted E. coli/pChvi cells. DNA sequencing of the luxR-luxl region reveals the presence of a promoter region of the kind typical for sigma 32 at the beginning of the luxl gene. In addition we find a LexA protein-DNA binding site in the non-consensus sequence for the -35 region of the PR operon. It is proposed that the regulatory protein-inducer complex displaces the LexA protein and allows the transcription of the right operon. SOS-inducing agents result in proteolysis of LexA protein and advance the onset of luminescence. sigma 32 enhances the transcription from the PR operon and thus initiates a positive control circuit. It seems that sigma 32 is the major controlling element in determining the onset of luminescence both in vivo and in vitro.

4-Butyrolactone↗
PubMedDate not supplied

Fusion of LuxA and LuxB and its expression in E. coli, S. cerevisiae and D. melanogaster.

Luciferase from Vibrio harveyi is encoded by two adjacent genes, luxA and luxB. The two genes were fused by replacing a segment extending from near the end of luxA into the N-terminal end of luxB by a synthetic oligonucleotide. The construction removed the TAA stop codon at the end of luxA, the intervening region of 26 base pairs, and the initial methionine of luxB. A Smal site was included at the junction between the two genes and an AatII site was created near the end of luxA without altering its amino acid sequence. In Escherichia coli the fused luxAB gene could be expressed to produce functional luciferase that gave about 20% of the activity in cells without the fusion. An out-of-frame ATG exists close to and preceding the ATG of the luxA gene. This was removed and the entire fused gene bracketed by several restriction enzyme sites. The fused luxAB gene was successfully expressed in Saccharomyces cerevisiae and Drosophila melanogaster by transferring it to appropriate plasmid vectors.

Amino Acid Sequence↗
PubMedDate not supplied

Formation of active bacterial luciferase between interspecific subunits in vivo.

Interspecific complementation between luxAs and luxBs from Vibrio harveyi, Vibrio fischeri, Photobacterium leiognathi and Xenorhabdus luminescens was examined in vivo. The individual genes from these species were cloned on different compatible plasmids or amplified by PCR and brought together to yield cis combinations without extraneous DNA. The beta subunits from V. harveyi and X. luminescens form active enzyme only with alpha subunits from one of these species. All other combinations yield active enzymes. The lack of activity of the V. harveyi and X. luminescens beta subunits with the alpha subunits from V. fischeri and P. leiognathi results from a lack of association. This was shown by in vivo competition in which these beta subunits were overproduced in comparison with the beta and alpha of V. fischeri. No reduction in light was found. Overall, the in vivo results parallel those found in vitro using isolated denatured subunits and renaturation by removal of the denaturant.

Bacteriophage lambda↗
PubMedDate not supplied

A phase I clinical and pharmacological profile of dacarbazine with autologous bone marrow transplantation in patients with solid tumors.

Dacarbazine (DTIC) is a chemotherapy drug which has antitumor activity at standard doses, exhibits a steep dose-response effect in vitro, and is associated with relatively few non-hematologic toxicities. These characteristics suggest a potential role for this drug in bone marrow transplant preparative regimens. To pursue this hypothesis, 16 patients with refractory solid tumors were enrolled in a phase I study of single agent DTIC to determine the dose of DTIC requiring bone marrow reinfusion and to define the dose-limiting toxicity and maximum tolerated dose when given with autologous bone marrow rescue. Pharmacokinetics were evaluated at the 4394 mg/m2 dose level. The marrow requiring dose was 2000 mg/m2 when given as a single intravenous (i.v.) infusion. The extramyeloid dose-limiting toxicity of DTIC was hypotension, with the maximum tolerated dose of DTIC being 3380 mg/m2 when given with bone marrow transplantation (BMT). Other toxicities were transient and tolerable. At 4394 mg/m2 of DTIC, plasma concentrations declined biexponentially with a terminal half-life of 3 hours. The mean clearance was 10.6 L/hr/m2 with a volume of distribution at steady state of 37.5 L/m2 and a mean maximum plasma concentration of 150 mcg/ml. One patient with melanoma developed a partial response of short duration after receiving 2600 mg/m2 of DTIC. Dacarbazine can be significantly dose escalated with an acceptable toxicity profile, when given with BMT. Future trials should focus on the addition of this drug to current BMT preparative regimens used for the treatment of patients with lymphoma.

Adult↗
PubMedDate not supplied

Sequence and properties of operator mutations in the bio operon of Escherichia coli.

The nucleotide-sequence changes occurring in newly isolated operator-constitutive mutations of the divergently transcribed bio operon have been determined. The observed point mutations are single GC leads to AT changes which occur at two symmetrical points in the hyphenated inverted repeat present in the control region. The changes at position -15 (with respect to the center of the inverted repeat) cause constitutivity of leftward operon expression and decreased expression of bioB, due to alteration of the -35 region of the rightward promoter. The change at position +15 is identical to one of the changes that Otsuka and Abelson (1978) detected in the bio p98 bio o34 double mutant. The location of the bio p131::IS1 insertion, which affects both leftward and rightward transcription, is also within the operator region. Both of the operator-constitutive mutations and the bio p131 insertion cause decreased repressor binding in vivo as shown by repressor titration tests on multicopy plasmids which bear them. The operator-constitutive mutations also decrease repressor binding in vitro, where added repressor fails to protect the TaqI site that is protected by repressor in bio o+ DNA. These results confirm several aspects of the model for bio operon regulation proposed by Otsuka and Abelson (1978).

Bacteriophage lambda↗
PubMedDate not supplied

[Regional mortality differences in Bavaria].

OBJECTIVE: In completion of a decision of the Bavarian Parliament we examined the regional mortality differences within Bavaria. DATA: The analysis was based on the number of deaths in Bavaria in the years of 2000-2002. Data on regional demographic and socioeconomic indicators were used to identify potential associations. METHODS: Deaths were analysed by cause of death and region. Crude and age standardised mortality rates were calculated. Additionally, we assessed the potential years of life lost in order to obtain some indication of the potential effects of preventive action. The association with likely explanatory factors was investigated on an ecological level. RESULTS: The regional mortality differences in Bavaria show a northeast-southwest gradient favouring the southwest, which reflects the socioeconomic situation within Bavaria. This may be due to the economic disadvantage northeast Bavaria had to endure as a result of its marginal location within a divided Europe. We found strong bivariate correlations of the mortality rate with individual socioeconomic factors (e. g. with available income: -0.582; with unemployment: +0.416; with the immigration rate: -0.473). Exploratory analysis suggest that about 50 % of the regional variation in mortality could be explained by socioeconomic factors. DISCUSSION: The results for cause of death indicate that behavioural factors in relation to socioeconomic aspects may well play a role in the mortality gradient. This will be the focus of a future piece of research of our unit.

Adolescent↗
PubMedDate not supplied

Interaction of hyperthermia with Taxol in human MCF-7 breast adenocarcinoma cells.

Hyperthermia treatments (43 degrees C, 1 h) were performed on exponentially growing MCF-7 breast adenocarcinoma cells at the beginning, middle, or end of 24 h incubations of the cells in vitro with Taxol (paclitaxel). When the cells were heated at the beginning or middle of the Taxol incubation, the hyperthermia treatment protected against the toxic effect of each of the Taxol concentrations examined (5, 10 and 100 nM). Consistent with earlier studies, Taxol treatment at 37 degrees C resulted in an accumulation of greater than 94% of the cells in G2/M at 24 h. Heating the cells at the middle or end of the Taxol treatment resulted in a similar accumulation. However, heat treatment during the first hour of Taxol exposure resulted in a significantly smaller percentage of cells (approximately 50%) in G2/M. HPLC analysis showed that at 37 degrees C, Taxol uptake into MCF-7 cells approached maximum within 0.25 h and increased only slightly more over the next 11.75 h. The parental Taxol level was markedly lower by 24 h. In contrast, 1 h hyperthermia treatments at the beginning or middle of the Taxol incubation resulted in higher Taxol concentrations at 12 and 24h, and higher intracellular concentrations overall than at 37 degrees C. These results indicate that hyperthermia inhibits Taxol related cell cycle effects and cytotoxicity, in spite of causing higher concentrations of Taxol to be present in heated cells.

Adenocarcinoma↗
PubMedDate not supplied

[ELISA and RT-PCR-based research of viruses in the ticks collected in the foci of Crimean-Congo fever in Kazakhstan and Tajikistan in 2001-2002].

Different species of ticks were found, in the territories of Kazakhstan and Tajikistan, to be infected with the virus of Crimean-Congo hemorrhagic fever (CKHF). The virologic evaluation included determination of antigen and RNA of the CKHF virus by ELISA and RT-PCR, respectively. The below tick species were found to be involved in the epidemic process: Hyalomma asiaticum, Dermacentor niveus (Kazakhastan) and Hyalomma anatolicum (Tajikistan). The results testify to the fact that Hyalomma ticks are the main carrier of the above virus in the Middle Asia. At the same time, Dermacentor niveus ticks are infection carriers in Kazakhstan.

Animals↗
PubMedDate not supplied

[Study of virus contamination of Ixodes ticks in the foci of Crimean-Congo hemorrhagic fever in Kazakhstan and Tajikistan].

The data on the contamination of different of ticks with Crimean-Congo hemorrhagic fever (CCHF) virus on the territory of Kazakhstan and Tajikistan were obtained. The methods of the evaluation of the virus contamination of ticks included the determination of the antigen and CCHF virus RNA by the methods of the enzyme immunoassay and the reverse transcription PCR respectively. Different tick species were found to be involved in the epidemic process: Hyalomma asiaticum, Dermatocentor niveus (Kazakhstan) and Hyalomma anatolicum (Tajikistan). The results obtained in this study confirmed that the main vector of CCHF virus in Central Asia were ticks of the genus Hyalomma, and in Kazakhstan the vectors of this virus also included ticks Dermatocentor niveus.

Animals↗
PubMedDate not supplied

[Adrenal adenoma disclosing after delivery].

Pregnancy and Cushing's syndrome are seldom found together (40 cases in the literature), since hyperadrenocorticism is often responsible for anovulation by gonadotropin suppression. We report the case of a 25-year old para II woman whose pregnancy was complicated by diabetes and arterial hypertension at 31 weeks and who received the conventional treatments (special diet, insulin therapy, pindolol). Caesarean section, motivated by premature rupture of the membranes, was performed at 37 weeks, delivering a healthy infant. The diagnosis of hypercortisolism with low ACTH level was made post partum. An adrenal tumour (the most frequent cause of Cushing's syndrome occurring during pregnancy) was removed after pre-operative treatment with ketoconazole, and endocrine functions returned to normal.

Adenoma↗
PubMedDate not supplied

Clinical engineering education in the high technology hospital.

The application of high technology in the critical care field has created two potential approaches: (1) development of critical care technicians to coordinate clinical engineering educational support; and (2) modification of the hospital organization to streamline communications between the clinical engineers and those they support. At one university hospital studied from 1978 to 1982, both the use of high technology equipment and the number of critical care technicians approximately doubled. With emphasis on technician coordination of engineering support, the in-service education lectures increased 134%, while the engineering staff and the corrective maintenance workload remained unchanged.

Biomedical Engineering↗