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C Jeppesen

Publications and source records attributed to C Jeppesen.

At least 19 recordsLinked to original sources
PubMed2001

Impact of polymer tether length on multiple ligand-receptor bond formation.

The promoters of cell adhesion are ligands, which are often attached to flexible tethers that bind to surface receptors on adjacent cells. Using a combination of Monte Carlo simulations, diffusion reaction theory, and direct experiments (surface force measurements) of the biotin-streptavidin system, we have quantified polymer chain dynamics and the kinetics and spatial range of tethered ligand-receptor binding. The results show that the efficiency of strong binding does not depend solely on the molecular architecture or binding energy of the receptor-ligand pair, nor on the equilibrium configuration of the polymer tether, but rather on its "rare" extended conformations.

Biotin↗
PubMed2000

[Legionella pneumophila in pool water].

We investigated 87 samples of pool water for the presence of Legionella. The samples were from cold water pools (< 28 degrees C) and from hot water pools (> 32 degrees C). Sampling was furthermore done on normal water samples, on water from the bottom of pools and of water from departure from the activated carbon filters. Legionella was not detected in any of the samples from cold water pools, whereas in the hot water pools 10% of the pool water samples and 80% of the water from the filters were infected with Legionella pneumophila. The highest concentrations of Legionella were found in the filter samples, whereas the concentrations in the pool water (10-100 cfu/liter) were not alarming. This investigation demonstrates the potential risk of presence of Legionella in hot water pools with activated carbon filters being the site with best growth potential. It should be stressed that a high level of disinfection (at least 1.0 mg free chlorine/liter and pH 7.2) is essential for the prevention of Legionella in pool water at higher temperatures.

Disinfection↗
PubMed2000

Pressure patches for membranes: the induced pinch of a grafted polymer.

Achieving control of membrane shape and topology is of crucial importance to regulate function and performance of many systems in the realms of biology, physics, and chemical sciences. The design of a kit of versatile microscopic tools for tuning the shapes of fluid membranes relies ultimately on the possibility of tailoring molecules for applying a given, well-chosen force, to the self-assembled interfaces. Here we discuss theoretically the ability of grafted polymers to perform as mesoscopic pressure patches. We compute the pressure that a grafted polymer applies to the supporting surface. We also show that this entropic pressure leads to a well-defined pinched form of the membranes. Moreover, new membrane-mediated forces result from the action of these pressure tools, enabling action upon their spatial distribution along the membrane surface.

Elasticity↗
PubMed1995

Media for Aeromonas spp., Plesiomonas shigelloides and Pseudomonas spp. from food and environment.

Several media are proposed particularly for the detection of Aeromonas spp. but also for Plesiomonas shigelloides and Pseudomonas spp. Some are for general purposes and others specifically for the examination of clinical, environmental or food samples. All media are selective, due to antibiotics, bile salts, dyes and other selective agents, as well as differential, primarily based on the ability of the microorganisms to ferment/not ferment carbohydrates. As with all selective media, the recovery of stressed cells is sometimes prevented and the competing flora is not always completely inhibited so that confirmatory tests need to be made on presumptive positive colonies. The choice of a specific medium for isolation of Aeromonas spp. will always depend on the type of sample to be examined and whether the investigator needs qualitative detection or quantitative recovery. The best medium for quantitative estimation of Aeromonas spp. from food and environmental samples seems to be starch ampicillin agar (SAA), though others might be recommended. There is a need for a comparative study including Rippey Cabelli agar (mA), ampicillin bile salts inositol xylose (MIX) agar, ampicillin dextrin agar (ADA), dextrin fuchsin sulphite agar (DFS) and starch glutamate ampicillin penicillin C-glucose agar (SGAP-10C) in addition to SAA. For routine analysis of environmental and food samples for P. shigelloides, spread plating on inositol brilliant green bile salts (IBB) and plesiomonas (PL) agars is recommended. For Pseudomonas spp., CFC agar permits quantitative recovery of both pigmented and non-pigmented strains from food and environmental samples, whilst at the same time inhibiting most other organisms.

Aeromonas↗
PubMed1991

Photochemistry of quinolylmethylisothioronium salts. Guanine selective DNA photocleavage reagents.

Quinolylmethylisothioronium salts (1a and 4a) cleave DNA upon irradiation. The cleavage is more than 10-fold enhanced by piperidine treatment and subsequently shows a high preference for guanines. Photolysis of 1a, 2a and 4a in water at lambda greater than 300 nm resulted in photoheterolysis. Irradiation of 1a in 2-propanol gave only products from photohomolysis, irradiation of 1a in methanol and 2a and 4a in 2-propanol resulted in products from both photoheterolysis and photohomolysis. Quantum yields for the disappearance of 1a in water and 2-propanol were determined. The presence or absence of oxygen had no effect in water, whereas oxidation products were observed upon irradiation in methanol and 2-propanol in the presence of oxygen. The guanine specific DNA photoreaction is proposed to take place by alkylation at N7 via the quinolylmethyl carbocation and thus to represent a photoalkylation.

Base Sequence↗
PubMed1990

DNA conformational analysis in solution by uranyl mediated photocleavage.

Uranyl mediated photocleavage of double stranded DNA is proposed as a general probing for DNA helix conformation in terms of minor groove width/electronegative potential. Specifically, it is found that A/T-tracts known to constitute strong distamycin binding sites are preferentially photocleaved by uranyl in a way indicating strongest uranyl binding at the center of the minor groove of the AT-region. The A-tracts of kinetoplast DNA show the highest reactivity at the 3'-end of the tract--as opposed to cleavage by EDTA/Fell--in accordance with the minor groove being more narrow at this end. Finally, uranyl photocleavage of the internal control region (ICR) of the 5S-RNA gene yields a cleavage modulation pattern fully compatible with that obtained by DNase I which also--in a more complex way--senses DNA minor groove width.

Animals↗
PubMed1990

Distribution and characteristics of Aeromonas in food and drinking water in Denmark.

A total of 970 Danish commercial foods and drinking water samples were examined for the presence of motile Aeromonas spp. With a detection limit of 10(2)/g the frequent prevalence in raw foods was confirmed. Aeromonas occurred in 7% of 779 samples of prepared foods; most frequently in whipped cream from ice cream parlors (28%) and mayonnaise salads (10%) with numbers occasionally exceeding 10(5)/g. The prevalence in drinking water was 28% with a detection limit of 1/100 ml. A hydrophila was the dominating species in both food and water. Hemolysin production was demonstrated in 37% of the 51 isolates tested with 10% having high titers.

Aeromonas↗
PubMed1990

Uranyl photoprobing of conformational changes in DNA induced by drug binding.

The effect on DNA conformation upon binding of the bis-intercalator, N,N'-diacridinyl spermidine is studied by uranyl mediated DNA photocleavage and gel retardation. It is shown that a characteristic A-tract correlated 10 base pair modulation of the uranyl photocleavage of bent (kinetoplast) DNA is suppressed upon binding of the diacridine. Likewise, the anomalous slow gel electrophoretic migration of bent-DNA is abolished by diacridine binding. At higher diacridine/DNA ratios a DNA conformation in which G-residues become hypersensitive to uranyl photocleavage is induced.

DNA↗
PubMed1989

Uranyl mediated photofootprinting reveals strong E. coli RNA polymerase--DNA backbone contacts in the +10 region of the DeoP1 promoter open complex.

Employing a newly developed uranyl photofootprinting technique (Nielsen et al. (1988) FEBS Lett. 235, 122), we have analyzed the structure of the E. coli RNA polymerase deoP1 promoter open complex. The results show strong polymerase DNA backbone contacts in the -40, -10, and most notably in the +10 region. These results suggest that unwinding of the -12 to +3 region of the promoter in the open complex is mediated through polymerase DNA backbone contacts on both sides of this region. The pattern of bases that are hyperreactive towards KMnO4 or uranyl within the -12 to +3 region furthermore argues against a model in which this region is simply unwound and/or single stranded. The results indicate specific protein contacts and/or a fixed DNA conformation within the -12 to +3 region.

Base Sequence↗
PubMed1989

Photofootprinting of drug-binding sites on DNA using diazo- and azido-9-aminoacridine derivatives.

It is demonstrated that DNA photofootprinting analysis of the intercalating depsipeptide echinomycin, and the minor groove-binders distamicyn, 4',6-diamidino-2-phenylindole (DAPI) and Hoechst 33258 can be performed using 9-[6-(2-diazocyclopentadienylcarbonyloxy)hexylamino]acridine (DHA) [Nielsen et al. (1988) Nucleic Acids Res. 16, 3877-3888] or 2-methoxy-6-azido-9-aminoacridine (MAA) [Jeppesen et al. (1988) Nucleic Acids Res. 16, 5755-5770]. Both the extent of the drug-binding sites and their relative strength can be determined with either reagent. DNA has the advantage of giving virtually sequence-uniform DNA photocleavage. On the other hand, structural changes in the DNA are detected by MAA. Using the 232-base-pair EcoRI-PvuII pUC19 restriction fragment, it is found that cleavage protection by distamycin, DAPI and Hoechst 33258 all require an (A.T)4 sequence, whereas protection by echinomycin was confined to a G + C-rich 8-base-pair region.

Aminoacridines↗
PubMed1988

A specific and efficient photoreaction between E. coli RNA polymerase and T+1 in the lacUV5 or deoP1 promoter.

Upon irradiation of the RNA polymerase-lacUV5 or deoP1 promoter complex with short wavelength ultraviolet light (lambda less than or equal to 300 nm) the polymerase is covalently crosslinked at an efficiency of greater than 10% to the first transcribed base of the template DNA strand when this is a thymine. The temperature dependence of this RNA polymerase-T+1 photoreaction strongly indicates a relation to the formation of the open complex. It is suggested that open complex formation is preceded or accompanied by a specific contact between the RNA polymerase and the first transcribed base of the DNA template.

Cross-Linking Reagents↗
PubMed1988

Photochemical cleavage of DNA by nitrobenzamides linked to 9-aminoacridine.

Nitrobenzamido ligands linked to the DNA intercalator 9-aminoacridine via poly(methylene) chains induce single-strand nicks in DNA upon irradiation with long-wavelength ultraviolet light (lambda greater than or equal to 300 nm). Optimal photocleavage activity was found for the reagent 9-[[6-(4-nitrobenzamido)hexyl]amino]-acridine. Removal of the acridinyl ligand or changing the position of the nitro group from the 4- to the 2-position caused a 10-fold decrease in photocleavage efficiency, whereas a change to the 3-position caused a 30-fold reduction. The DNA cleavage was 5-fold enhanced by subsequent piperidine treatment and showed some sequence dependency with predominant cleavage at G and T residues. Furthermore, significant differences in cleavage preference were observed when the poly(methylene) linker length was changed.

Aminoacridines↗
PubMed1988

Uranyl salts as photochemical agents for cleavage of DNA and probing of protein-DNA contacts.

Single-strand DNA nicks are induced by uranyl nitrate or uranyl acetate in combination with long-wavelength (lambda approximately 420 nm) ultraviolet irradiation. The nicks occur randomly with respect to the DNA sequence. Using the lambda-repressor/ORI operator DNA system it is shown that uranyl salts can be used to photofootprint protein contacts with the DNA backbone.

Bacteriophage lambda↗