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Biomedical subjects

K Riedel

Publications and source records attributed to K Riedel.

At least 37 records · Page 2Linked to original sources
PubMed1998

Screening of xenobiotic compounds degrading microorganisms using biosensor techniques.

A screening device based on microorganisms immobilised onto a Clark-type oxygen electrode was used to monitor the potential of these microorganisms for the degradation and detection of xenobiotic compounds especially their chlorinated derivatives. The sensitivity and specificity of various species of Pseudomonas, Sphinomonas, Ralstonia, Rhodococcus were characterised in relation to xenobiotic compounds by using biosensor techniques. The following groups of xenobiotics were subjects of investigation: chlorophenols, chlorobenzoates, 2,4-D, PCB, dibenzofurane and their putative intermediates. Using this simple setup it proved possible to screen microbial strains for their potential to catabolize aromatic and chloroaromatic compounds under oxygen consumption. In a kinetic regime, a reproducible signal was obtained within minutes. Based on these results the sensor technique was a suitable method for the rapid characterization of microorganisms and allowed to gather information about the substrate spectrum.

2,4-Dichlorophenoxyacetic Acid↗
PubMed1998

Intramolecular synergism in an engineered exo-endo-1,4-beta-glucanase fusion protein.

Exoglucanase CelY and endoglucanase CelZ from the cellulolytic thermophile Clostridium stercorarium act in synergism to hydrolyse cellulosic substrates. To increase the efficiency of the hydrolytic degradation process, an artificial multienzyme carrying both enzymatic activities on one polypeptide chain was constructed by gene fusion. A segment of CelZ, CelZdeltaBB'C (designated CelZC'), comprising the catalytic domain and the adjacent domain C' homologous to the cellulose-binding domain family IIIc, was fused to the C-terminus of CelY, yielding the fusion protein CelY-CelZC', designated CelYZ. The large fusion protein (170 kDa) could be isolated from a recombinant Escherichia coli strain in its intact form retaining the pronounced thermostability of the fusion partners. As a true multienzmye, CelYZ exhibited both exoglucanase and endoglucanase activities. The cellulolytic activity of the fusion protein was three- to fourfold higher than the sum of the individual activities. Dilution experiments showed that the enhanced cellulolytic activity of the multienzyme resulted from intramolecular synergism of the fusion partners. The product profiles and the kinetic constants of cellulose hydrolysis support a new mechanistic model proposed for explaining the co-operativity of the two catalytic domains within the multienzmye.

Artificial Gene Fusion↗
PubMed1997

DNA adducts in human placenta in relation to tobacco smoke exposure and plasma antioxidant status.

The DNA adduct 8-hydroxy-2'-deoxyguanosine (8-OHdG) has been widely used as a biomarker for oxidative stress. Bulky DNA adducts, which are detectable by the 32P-postlabelling method, provide evidence for exposure to and metabolic activation of large, mainly apolar compounds, e.g. polycyclic aromatic hydrocarbons. We determined both types of adducts in placental tissues of 30 term pregnancies and related the adduct levels to the exposure to tobacco smoke and the plasma antioxidant status. Urine and plasma continine concentrations were used to select 10 nonsmokers, 9 nonsmokers exposed to environmental tobacco smoke (ETS) and 11 smoking women. Placental levels of 8-OHdG were 0.84 +/- 0.11, 0.90 +/- 0.21 and 0.83 +/- 0.20/10(5) deoxyguanosine bases (dG) for nonsmokers, nonsmokers exposed to ETS and smokers, respectively. The differences between the groups were not significant. Smoking women had significantly lower plasma vitamin C and beta-carotene concentrations than nonsmoking women or nonsmoking women exposed to environmental tobacco smoke. The 8-OHdG adduct level in placental DNA was inversely correlated with the plasma vitamin E concentration (r = -0.47, P < 0.05). There was no association between placental 8-OHdG adducts and vitamin A, C and beta-carotene in plasma. In total, 15 different adducts could be identified in the 30 placenta samples by the 32P-postlabelling method. There was a strong inter-individual variation in both the number of adducts and adduct intensities. No smoking-related or vitamin-related effects on adduct patterns or intensities were found. Our findings suggests that, within the limits of the methods used, tobacco smoke exposure during pregnancy does not lead to a measurable increase in placental DNA adduct levels and that vitamin E appears to have a protective effect on placental 8-OHdG formation.

8-Hydroxy-2'-Deoxyguanosine↗
PubMed1997

Rapid physiological characterization of microorganisms by biosensor technique.

Eleven microorganisms, Arxula adeninivorans LS3, Candida boidinii DSM 70034, Candida lactis-condensi DSM 70635, Pichia jadinii DSM 2361, Pichia minuta DSM 7018, Kluyveromyces lactis DSM 4394, Pseudomonas putida DSM 50026, Alcaligenes sp. DSM 30002, Arthrobacter nicotianae DSM 20123 as well as Issatchenkia orientalis DSM 70077 and Rhodococcus erythropolis DSM 311 were characterized by the sensor technique by injection of 30 different substrates and substrate mixtures. The obtained data which are based on the determination of respiratory rate of microorganisms are similar to physiological characteristics obtained with conventional methods. In comparison to these conventional methods the sensor technique works much more rapid and permits quantification of the data. Therefore, the described technique provides an alternative method for the characterization of microorganisms.

Bacterial Physiological Phenomena↗
PubMed1997

Physiological characterization of a microbial sensor containing the yeast Arxula adeninivorans LS3.

The yeast Arxula adeninivorans LS3 is a suitable organism for use as part of a microbial sensor. In combination with an amperometric oxygen electrode the sensor offered a possibility for the physiological characterization of this yeast. About 300-400 measurements could be carried out with a single Arxula sensor. The microbial sensor was remarkably stable for over 35 days, when kept at 37 degrees C during the operation time and at room temperature overnight. The physiological characteristics of Arxula adeninivorans LS3 obtained with the sensor technique were identical to the data obtained with the conventional techniques. However, the sensor technique makes it additionally possible to quantify the physiological data. So the substrates ribose, citric acid, glycerol, oil and benzoate produced signals lower than 10% in comparison to the glucose signal. Fructose, xylose, sucrose, maltose, gentianose, glucosamine, glutamic acid, tryptophan, butyric acid, lauryl acid and propionic acid reached 10-70%, galactose, alanine, glycine, lysine and methionine signals were similar to the glucose signal whereas acetic acid, ethyl alcohol, capron acid, capryl acid and caproic acid reached the highest signals up to 434%.

Amino Acids↗
PubMed1996

Urinary mutagenicity and thioethers in nonsmokers: role of environmental tobacco smoke (ETS) and diet.

The urinary excretion of mutagens and thioethers was investigated in a controlled diet study and in two field studies. A diet containing charcoal-broiled meat and other items rich in mutagenic compounds increased the urinary mutagenicity as assessed in Salmonella typhimurium strain TA98 with metabolic activation approximately 46-fold compared to a diet low in mutagens. The excretion of thioethers after ingestion of the diet rich in mutagens also increased significantly when compared to the diet low in mutagens. The increase was associated with the content of preformed thioethers in the diet. In the first field study with 21 nonsmokers, urinary mutagenicity as assessed in Salmonella typhimurium strain TA98 and excretion of thioethers showed no relation to either the self-reported exposure to environmental tobacco smoke (ETS) or to serum cotinine concentrations used as an objective marker for ETS exposure. In the second field study, urinary mutagenicity was determined with a tobacco-smoke sensitive Salmonella typhimurium strain YG1024 with metabolic activation. No correlation was found between the mutagenic activity in urine and ETS exposure duration, nicotine on the personal sampler, cotinine in saliva and cotinine in urine. Our results suggest that real-life ETS exposure does not measurably increase either urinary mutagen or urinary thioether excretion. Furthermore, diet seems to be the most important source for both urinary mutagen and thioether excretion in nonsmokers.

Adolescent↗
PubMed1996

Analysis of a Thermotoga maritima DNA fragment encoding two similar thermostable cellulases, CelA and CelB, and characterization of the recombinant enzymes.

Recombinant Escherichia coli clones displaying thermostable beta-glucanase activity were isolated from two different gene libraries of the hyperthermophilic bacterium Thermotoga maritima MSB8 (DSM 3109), and the nucleotide sequence of a 1,4-beta-glucanase gene designated celA was determined. Amino-terminal sequencing of cellulase I previously detected in T. maritima cells indicated that the celA gene encodes this beta-glucanase, which is now designated CelA. CelA, which has a calculated molecular mass of 29,732 Da, was purified from a recombinant E. coli strain to apparent homogeneity as judged by SDS-PAGE with a 44% yield. The enzyme was most active against soluble substrates such as mixed-linkage beta-glucan and CM-cellulose. CelA displayed remarkable thermostability, which was enhanced in the presence of high concentrations of salt. Downstream of the celA gene we found a second open reading frame, celB, whose nucleotide sequence was 58% identical to celA. Experimental proof that celB also encodes a beta-glucanase was obtained by separation from celA and expression in E. coli under the control of an efficient host promoter. According to the deduced amino acid sequences, CelB, in contrast to CelA, contains a signal peptide at the amino terminus. CelB and CelA had similar substrate specificities and temperature optima, but differed in their pH optima. Also, the addition of salt had a less stabilizing effect on CelB than on CelA. Nine 30 bp direct repeats, each itself representing a sequence with imperfect dyad symmetry, were detected upstream of the celA-celB cellulase gene cluster.

Amino Acid Sequence↗
PubMed1994

Genetic polymorphisms of the angiotensin II type 1 (AT1) receptor gene.

Numerous essential, physiological effects on the cardiovascular system are attributable to angiotensin II (Ang II). Because of this we can assume that genetic changes in the specific receptor of Ang II (Ang II type 1 receptor gene, AT1) play a decisive role in the occurrence of cardiovascular disease associated with blood pressure regulation, vascular tone, cardiac and vascular growth process. To test this hypothesis, we examined the presence of polymorphisms within the coding region of the AT1 gene using polymerase chain reaction (PCR) and subsequent non-radioactive sequencing of samples from a control group with no previous history of cardiovascular complaint in individuals or immediate family. Using the Taq-sequencing procedure we found polymorphic sites, especially in the 5' region of the gene (base pair positions 9, 16, 87, 133, 186), two of which led to an exchange of the amino acid (amino acid 6: Ser<==>Pro, amino acid 45: Gly<==>Arg). Together with the silent polymorphism at base pair position 573, which our group established previously, an additional polymorphism in the 3' region of the gene was discovered. This, however, did not confer any changes in amino acid sequence. In a preliminary study we found no association between the distribution of the C/T573 polymorphic site and cardiovascular disease, such as essential hypertension (n = 20) coronary artery disease (n = 16) hypertrophic cardiomyopathy (n = 12) or dilated cardiomyopathy (n = 21). Further studies will be needed to determine to what extent the polymorphisms described are associated with cardiovascular disease.

Amino Acid Sequence↗
PubMed1993

Photodynamic laser therapy of basal-cell carcinoma of the lid.

Photodynamic therapy (PDT) remains an experimental approach for the treatment of small, mainly superficial malignant tumors. When given intravenously, hematoporphyrin derivative (HpD) selectively photosensitizes tumor tissue. Activated by light of 630 nm wave-length, HpD leads to tumor necrosis. This paper presents the results of PDT to eyelid basal-cell carcinomas in 21 patients. All lesions primarily responded to the treatment and became necrotic. A generalized photosensitization lasting for more than 4 weeks was seen in all patients. In five patients, lid malformations due to scar formation were noted, being marked in three cases. Ten patients showed a recurrence of tumor after 3-12 months. At present, PDT has no advantage over well-established therapies for basal-cell carcinomas of the eyelid.

Aged↗
PubMed1991

[Biosensors for the determination of phenol and benzoate on the basis of Rhodococcus cells and enzyme extracts].

An amperometric biosensor for determination of phenol, cresol, benzoate and 2-methyl-4-chlorophenol using Rhodococcus-cells and enzyme extracts of Rhodococcus has been developed. The influence of cultivation of Rhodococcus-cells and preincubation of the biosensor with desired substrate on sensibility and specificity was been investigated. In relation to cultivation and preincubation the Rhodococcus sensor was high specific to benzoate or phenol and cresol. A linear range was obtained for phenol and benzoate up to 80 mumol and for 2-methyl-4-chlorophenol up to 400 mumol. The biosensor using enzyme extracts show a higher specificity, it is but necessary NADPH. A further disadvantage is the little measuring range of this sensor.

Benzoates↗
PubMed1990

Amperometric determination of ammonium ions with a microbial sensor.

A sensor for NH+4 ions has been developed, which consists of immobilized micro-organisms (Bacillus subtilis, Pseudomonas aeruginosa, Trichosporon cutaneum) in combination with an electrochemical transducer. This sensor is based on the measurement of acceleration of respiration after addition of NH+4 in the presence of glucose. The physiological background of this signal and its connection with NH+4 ion uptake and/or metabolism is discussed. The response time of the sensor is about 5-10 s for NH+4 ions. A linearity was observed between 0.005 and 0.15 mmol dm-3 NH+4 ions. The sensitivity of the sensor remained almost constant for 12 days. The sensor was used to determine NH+4 ions in a microbial fermentation broth.

Bacillus subtilis↗
PubMed1988

Prediction of the risk of hereditary retinoblastoma, using DNA polymorphisms within the retinoblastoma gene.

Using molecular cloning, we earlier isolated the "retinoblastoma gene"; mutations or deletions at this locus are associated with the hereditary predisposition to some human cancers, especially retinoblastoma and osteosarcoma. To develop diagnostic tests for such a predisposition, we identified restriction-fragment-length polymorphisms (RFLPs) within the retinoblastoma gene and tested their usefulness in predicting the risk of cancer in 20 families with members who had hereditary retinoblastoma. We were able to make predictions in 19 of the 20 kindreds. In 18 kindreds, we demonstrated a consistent association of marker RFLPs with the mutation predisposing to retinoblastoma. In the 19th kindred, there may be a lack of cosegregation of the DNA polymorphisms within the gene and the site of the mutation predisposing to retinoblastoma. However, there is uncertainty about the clinical diagnosis of the retinal lesion in a key member of this kindred; if the lesion is not a retinoblastoma, there is no discrepancy between the DNA polymorphisms and the retinoblastoma trait. We conclude that it is feasible and clinically useful to use these DNA polymorphisms to determine the risk of cancer.

Alleles↗