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At least 775 records · Page 43Linked to original sources
PubMed2006

180 degree unidirectional bond rotation in a biaryl lactone artificial molecular motor prototype.

A bifunctional biaryl lactone has been synthesized that should be capable of iterative unidirectional aryl-aryl bond rotation via: (1) a diastereoselective lactone ring opening, (S)-1 to (P,S)-2 or (M,S)-2; (2) a chemoselective lactonization, (P,S)-2 or (M,S)-2 to (S)-3; and (3) a chemoselective hydrolysis, (S)-3 to (S)-1. Preliminary results of a racemic sample have indicated unidirectional 180 degrees rotation with very high directional selectivity per individual artificial molecular motor molecule through the first two steps of this sequence. [reaction: see text]

Borohydrides↗
PubMed1997

Alzheimer's disease amyloid beta-protein forms Zn(2+)-sensitive, cation-selective channels across excised membrane patches from hypothalamic neurons.

We have previously shown that the 40-residue peptide termed amyloid beta-protein (A beta P[1-40]) in solution forms cation-selective channels across artificial phospholipid bilayer membranes. To determine whether A beta P[1-40] also forms channels across natural membranes, we used electrically silent excised membrane patches from a cell line derived from hypothalamic gonadotrophin-releasing hormone GnRH neurons. We found that exposing either the internal or the external side of excised membrane patches to A beta P[1-40] leads to the spontaneous formation of cation-selective channels. With Cs+ as the main cation in both the external as well as the internal saline, the amplitude of the A beta P[1-40] channel currents was found to follow the Cs+ gradient and to exhibit spontaneous conductance changes over a wide range (50-500 pS). We also found that free zinc (Zn2+), reported to bind to amyloid beta-protein in solution, can block the flow of Cs+ through the A beta P[1-40] channel. Because the Zn2+ chelator o-phenanthroline can reverse this blockade, we conclude that the underlying mechanism involves a direct interaction between the transition element Zn2+ and sites in the A beta P[1-40] channel pore. These properties of the A beta P[1-40] channel are rather similar to those observed in the artificial bilayer system. We also show here, by immunocytochemical confocal microscopy, that amyloid beta-protein molecules form deposits closely associated with the plasma membrane of a substantial fraction of the GnRH neurons. Taken together, these results suggest that the interactions between amyloid beta-protein and neuronal membranes also occur in vivo, lending further support to the idea that A beta P[1-40] channel formation might be a mechanism of amyloid beta-protein neurotoxicity.

Amyloid beta-Peptides↗
PubMed2003

Cross-linking strategy for molecular recognition and fluorescent sensing of a multi-phosphorylated peptide in aqueous solution.

In the research field of molecular recognition, selective recognition and sensing of phosphorylated protein surfaces is strongly desirable both for elucidation of protein-protein recognition at the molecular level and for regulation of signal transduction through protein surfaces. Here we describe a new strategy for molecular recognition of a multi-phosphorylated peptide using intrapeptide cross-linking on the basis of coordination chemistry. The present artificial receptor can selectively bind to doubly phosphorylated peptide through multiple-point interactions and fluorescently sense the binding event with an association constant of more than 106 M-1 in neutral aqueous solution.

Circular Dichroism↗
PubMed2006

Selection and syntheses of tentacle type peptides as 'artificial' lectins against various cell-surface carbohydrates.

Sialyl Lewis X and its derivatives are cell-surface carbohydrates that are involved in cell-cell recognition by carbohydrate-mediated interactions. Unfortunately, owing to the similarities between carbohydrates only a limited number of tools are available for their differentiation. In this study, we prepared a selected phage-displayed peptide library against LeX (2), SLN (3), or LN (4), which compared to sLeX (1) lack sialic acid, fucose, and both sialic acid and fucose from constituents, respectively. Sequences of the selected peptides, prepared as tentacle type dimeric peptides, were prepared and shown to have micromolar affinities for the cognate carbohydrates. The specificities displayed by these 'artificial' lectins overwhelm those of natural lectins. These results suggest that they can serve as useful tools to detect changes in the terminal monosaccharide of cell-surface carbohydrates.

Binding Sites↗
PubMedDate not supplied

Optimum selection of an implantable secondary battery for an artificial heart by examination of the cycle life test.

An implantable secondary battery is one of the key components in a total artificial heart system. Because a 2 year cycle life is required, the cycle life of the secondary battery as well as its charge and discharge properties are important parameters for selection of an appropriate battery. We carried out cycle life tests on four kinds of rechargeable batteries (a Ni-MH secondary battery, a Ni-Cd secondary battery, a Li-ion battery with a graphite anode, and a Li-ion battery with a nongraphitizable carbon electrode) to determine their suitability as implanted back-up batteries. Each of the batteries was charge/discharge cycled at 37 degrees C to 39 degrees C using a charge current of 1 C ampere, and they were each fully discharged under either pulsatile discharge loads, which mimicked pulsatile operation, or a nonpulsatile load equivalent to the average of the pulsatile loads. The two Li-ion batteries made by different manufacturers both met the minimum requirement of cycle life of more than 1,500 cycles, considering safety coefficient regardless of the discharge pattern. In addition, the temperature increase of these Li-ion batteries (3 degrees C) was lower than that of Ni-Cd and Ni-MH batteries (15-25 degrees C). Out of these four batteries, the two Li-ion batteries are the most suitable for use in a totally implantable artificial heart system.

Cadmium↗
PubMed2000

Design and evolution of artificial M13 coat proteins.

Using simple design and selective pressure, we have evolved an artificial M13 bacteriophage coat protein. M13 coat proteins first reside in the bacterial inner membrane and subsequently surround the DNA core of the assembled virus. The artificial coat protein (ACP) was designed and evolved to mimic both functions of the natural M13 coat proteins, but with an inverted orientation. ACP is a non-functional coat protein because it is not required for the production of phage particles. Instead, it incorporates into a phage coat which still requires all the natural coat proteins for structural integrity. In contrast with other M13 coat proteins, which can display polypeptides as amino-terminal fusions, ACP permits the carboxy-terminal display of large polypeptides. The results suggest that viruses can co-opt host membrane proteins to acquire new coat proteins and thus new functions. In particular, M13 bacteriophage can be engineered for new functions, such as carboxy-terminal phage display.

Amino Acid Sequence↗
PubMed1989

Effect of water and artificial saliva on mechanical properties of some denture-base materials.

Two artificial saliva samples selected on the basis of being chemically and physically similar to natural saliva were used as saturation media so that we could investigate their effects on mechanical properties of four denture-base materials, and the results were compared with the effect of water on the same materials. Diffusion coefficients in the more viscous saliva were different from those in water but, in general, mechanical properties were similarly affected in all liquids, indicating that the aqueous phase of the artificial medium was a major factor influencing the results.

Acrylic Resins↗
PubMed1999

Conformational dynamics and molecular interaction reactions of recombinant cytochrome p450scc (CYP11A1) detected by fluorescence energy transfer.

Bovine adrenocortical cytochrome P450scc (P450scc) was expressed in Escherichia coli and purified as the substrate bound, high-spin complex (16.7 nmol of heme per mg of protein, expression level in E. coli about 400-700 nmol/l). The recombinant protein was characterized by comparison with native P450scc purified from adrenal cortex mitochondria. To study the interaction of the electron transfer proteins during the functioning of the heme protein, recombinant P450scc was selectively modified with fluorescein isothiocyanate (FITC). The present paper shows that modified P450scc, purified by affinity chromatography using adrenodoxin-Sepharose to remove non-covalently bound FITC, retains the functional activity of the unmodified enzyme, including its ability to bind adrenodoxin. Based on the efficiency of resonance fluorescence energy transfer in the donor-acceptor pair, FITC-heme, we calculated the distance between Lys(338), selectively labeled with the dye, and the heme of P450scc. The intensity of fluorescence from the label dramatically changes during: (a) denaturation of P450scc; (b) changing the spin state or redox potential of the heme protein; (c) formation of the carbon monoxide complex of reduced P450scc; (d) as well as during reactions of intermolecular interactions, such as changes of the state of aggregation, complex formation with the substrate, binding to the electron transfer partner adrenodoxin, or insertion of the protein into an artificial phospholipid membrane. Selective chemical modification of P450scc with FITC proved to be a very useful method to study the dynamics of conformational changes of the recombinant heme protein. The data obtained indicate that functionally important conformational changes of P450scc are large-scale ones, i.e. they are not limited only to changes in the dynamics of the protein active center. The results of the present study also indicate that chemical modification of Lys(338) of bovine adrenocortical P450scc does not dramatically alter the activity of the heme protein, but does result in a decrease of protein stability.

Adrenal Cortex↗
PubMedDate not supplied

Small RNA sequences are readily stabilized by inclusion in a carrier rRNA.

This laboratory previously showed that an RNA derived from 5S ribosomal RNA could be used as a carrier to harbor a nucleic acid "tag" for monitoring genetically engineered or naturally occurring bacteria. The prototype system expressed a specific tagged RNA that was stable and accumulated to high levels. For such a system to be useful there should, however, be little limitation on the sequence composition and length of the insert. To test these limitations, a collection of insertion sequences were created and introduced into the artificial 5S rRNA cassette. This library consisted of random 13- and 50-base oligonucleotides that were inserted into the carrier RNA. We report here that essentially all of the insert-containing RNAs are stable and accumulate to detectable levels. Tagged RNAs were produced by both plasmid-borne and chromosomally integrated expression systems in E. coli and several Pseudomonas strains without obvious effect on the host cell. It is anticipated that in addition to its intended use in environmental monitoring, this system can be used for in vivo selection of useful artificial RNAs. Because the carrier lends stability to the RNAs, the system may also be useful in RNA production.

Base Sequence↗
PubMed1983

Structure of dairy cattle breeding in Western Europe and comparisons with North America.

The cattle population of Western Europe is slightly smaller than that of the United States but contains 32 million dairy cows versus 11 million. The dairy herd provides 80% of the beef produced against 20% in the United States. The dairy cow population in the European Economic Community consists of 15 million Friesian type cows and 10 million non-Friesian, making up 29 separate breeding populations. The structure and organization of the breeding program in these 29 populations are described. A strong inflow of North American genetic material (Holstein into the Friesian populations. Brown Swiss and Red Holstein into the others), which has been going on for some years, is quantified. Many European populations will be more than 50% North American in genetic constitution within a decade. The reasons for this shift in breeding policy are discussed. A method is introduced for describing the effectiveness of an artificial insemination bull selection program by numbers of bulls tested per million inseminations and lifetime usage of selected bulls. This method is used to compare the breeding programs of 10 North American breeding organizations with those of 20 European and 2 New Zealand populations. In general, the European populations are making much higher investments in bull testing, whereas the North American organizations tend to have higher rates of bull usage.

Animals↗
PubMed2003

A macrocyclic zinc(II) fluorophore as a detector of apoptosis.

Our originally designed dansylamidoethylcyclen 4 as a biomimetic Zn(2+)-selective fluorophore has been demonstrated to be a good detector of the apoptosis (induced by an anticancer agent, etoposide, and H(2)O(2)) in cancer cells such as HeLa and HL60 cells. The macrocyclic Zn(2+) ligand 4 (mostly as a deprotonated form) is cell-permeable to show weak fluorescence (emission at 550 nm), which forms a strong fluorescent 1:1 Zn(2+) complex 5 (emission at 530 nm) when Zn(2+) is incorporated into the cells by a zinc(II) ionophore pyrithione. Thus formed, Zn(2+) complex 5 is cell-impermeable and remains intact over a few hours. When apoptosis in HeLa or HL60 cells is artificially induced, 4 selectively and strongly stains apoptotic cells only at early stages, which was verified by using the conventional apoptosis detection probe annexin V-Cy3. Detection of the apoptotic cells by 4 was perhaps due to significantly increased free Zn(2+) flux at early stages of apoptosis. Apoptotic detection by 4 has been compared with a presently available Zn(2+) fluorophore, Zinquin 1. We present that 4 has advantages in detection of apoptosis over annexin V-Cy3 and Zinquin 1.

Apoptosis↗
PubMed1996

A pericentric inversion of chromosome six in a patient with Peutz-Jeghers' syndrome and the use of FISH to localise the breakpoints on a genetic map.

Karyotypic analysis in a patient with Peutz-Jeghers' syndrome demonstrated a pericentric inversion on chromosome 6. Further investigation was undertaken using fluorescence in situ hybridisation (FISH) with yeast artificial chromosome clones selected to contain genetic markers from chromosome 6, and a probe for the centromeric alphoid repeat array. This analysis located one inversion breakpoint within the alphoid array, in a 1-cM interval between D6S257 and D6S402, and the other in a 4-cM interval between D6S403 and D6S311. The oestrogen receptor gene locus (ESR) is excluded from the latter interval.

Adult↗
PubMed1999

Comparison of accuracy between compression- and injection-molded complete dentures.

STATEMENT OF PROBLEM: A clinically significant incisal pin opening may occur after processing complete dentures if a compression molding technique is used. To recover the proper vertical dimension of occlusion, a time-consuming occlusal adjustment is necessary that often destroys the anatomy of the artificial teeth. A new injection molding process claims to produce dentures that require few, if any, occlusal adjustments in the laboratory after processing. PURPOSE: This laboratory study compared incisal pin opening, dimensional accuracy, and laboratory working time for dentures fabricated by this new injection system with dentures constructed by the conventional compression molding technique. MATERIAL AND METHODS: Two groups of 6 maxillary and 6 mandibular dentures were evaluated as follows: group 1 (control), Lucitone 199, compression molded with a long cure cycle; and group 2, Lucitone 199, injection molded with a long cure. Incisal pin opening was measured with a micrometer immediately after deflasking. A computerized coordinate measuring machine was used to measure dimensional accuracy of 3-dimensional variations in selected positions of artificial teeth in 4 stages of denture fabrication. Analysis of variance (ANOVA) and t tests were performed to compare the groups. RESULTS: A significant difference was found in pin opening between groups (t test). Horizontal dimensional changes evaluated with repeated measures ANOVA revealed no significant differences between groups. However, analysis of vertical dimensional changes disclosed significant differences between the groups. There was no appreciable difference in laboratory working time for flasking and molding denture bases between the injection and compression molding techniques when polymethyl methacrylate resin was used. CONCLUSION: The injection molding method produced a significantly smaller incisal pin opening over the standard compression molding technique. The injection molding technique, using polymethyl methacrylate, was a more accurate method for processing dentures. There were no appreciable differences in laboratory working time between the injection and compression molding techniques.

Analysis of Variance↗
PubMed1975

The value of the nose width as an esthetic guide in prosthodontics.

A radiographic method was used to measure the interalar and interalar-fold widths of the nose on 80 men and women. These distances were compared to the subjects' intercanine distances as measure on artificial stone casts. In 56 of the subjects, the width of the skeletal nasal aperture was measured and compared to the intercanine distance. From the results of this study, the following conclusions can be drawn. 1. There was no significant relationship between the intercanine distance and the interalar width of the nose in the 80 men and women who served as subjects in this study. 2. There was no significant relationship between the intercanine distance and the interalar-fold width of the nose in the 80 men and women in this study. 3. The presence or absence of a significant relationship between the intercanine distance and the width of the skeletal nasal aperture was not demonstrated conclusively in this study. 4. The results of this study show that the width of the nose would not be a reliable guide for selecting or arranging artificial anterior teeth, provided one concurs that they should be the same size and shape and occupy the same position as their natural predecessors.

Adult↗
PubMed2006

Concept and development of a computerized positioning of prosthetic teeth for complete dentures.

To date, CAD/CAM technology has made no noteworthy inroads into removable dentures. We want to present a new area of application for this in our study. Models of the maxilla and edentulous mandible were 3D scanned. The software detects and automatically reconstructs the reference structures that are anatomically important for the set-up of artificial teeth, such as the alveolar ridge centerlines and the interalveolar relations between the alveolar ridges. In a further step, the occlusal plane is semiautomatically defined and the front dental arch is designed. After these design features have been determined, artificial teeth are selected from a database and set up automatically. The dental technician can assess the esthetics and function of the suggested dental set-up on the computer screen and make slight corrections if necessary. Summarizing: The interplay of hardware and software components within on integrated solution including conversion of the "virtual" into a real positioning of prosthetic teeth is presented.

Alveolar Process↗
PubMed1995

Artificial neural network for diagnosis of acute pulmonary embolism: effect of case and observer selection.

PURPOSE: To compare the diagnostic performance of an artificial neural network (ANN) with that of physicians in patients with suspected pulmonary embolism (PE). MATERIALS AND METHODS: An ANN was developed to predict PE by using findings from ventilation-perfusion lung scans and chest radiographs. First, the network was evaluated on 1,064 cases from the Prospective Investigation of Pulmonary Embolism Diagnosis (PIOPED) study that had a definitive angiographic outcome. An upper and lower bound of its diagnostic performance was provided depending on case difficulty. Then, the network was tested on 104 patients with suspected PE in whom pulmonary angiography was essential for diagnosis. The diagnostic performance of the ANN was compared with that of (a) two nuclear medicine physicians who read the scans for the needs of this study and (b) the nuclear medicine physicians who originally read the scans. The effects of case and observer selection on performance were addressed. RESULTS: The ANN outperformed the physicians when they used the PIOPED criteria for categoric assessment, and it performed as well as the two study physicians on the basis of their probability assessments. CONCLUSION: The ANN can detect or exclude PE in a highly selected group of difficult cases with a consistency equivalent to that of very experienced physicians.

Algorithms↗
PubMed1991

The long-term results of artificial sphincters in children.

To determine the long-term efficacy of the artificial urinary sphincter, 36 consecutive children in whom a prosthesis was implanted between August 1978 and July 1985 were followed for a minimum of 5 years and re-evaluated within the last 3 months. Of the 36 sphincters 27 (75%) are currently in place; 2 of these 27 sphincters are dysfunctional due to fluid leakage. Of the 25 functioning sphincters 14 have required no further prosthetic operation, 10 needed 1 revision and 1 patient had 5 revisions. Fluid leakage, occurring in 12 patients, was the most common complication requiring reoperation. Twenty patients are completely continent (11 of whom without any medication) and 5 are occasionally damp. The over-all success rate at 2 and 5 years was 84 and 62%, respectively. The mean survival time of the prosthesis was 7.2 years and the mean standard interval was greater than 10.5 years. Patients with higher balloon pressures (81 to 100 cm. water) had more complications, and a decreased rate of success than those with lower pressure balloons (51 to 80 cm. water, p = 0.02). There was no difference in success rates between boys and girls (p = 0.98), although girls who had a prior bladder neck operation tended to have a higher rate of cuff erosion. Sphincters placed after 1980 (model AS800) had a lower reoperation rate than those placed earlier. In selected instances, the artificial urinary sphincter appears to be a viable long-term alternative for management of children with intractable incontinence who have either failed or are unsuitable for other methods of treatment.

Child↗