Search PubMed⌕ Search

SEARCH · Search PubMed

Results for “Biological Resolution”

Search indexed PubMed citations on genomics, clinical trials, systematic reviews and public health. Explore titles, authors and supplied subject terms, then open the PubMed record.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 829 records · Page 46Linked to original sources
PubMed1989

The separation of [32P]inositol phosphates by ion-pair chromatography: optimization of the method and biological applications.

We have developed an ion-pair reverse-phase HPLC method to measure inositol phosphates in 32P-labeled cells. The different chromatographic parameters were analyzed to optimize the resolution of the 32P-labeled metabolites. Analysis of inositol phosphates in biological samples was improved by a single charcoal pretreatment which eliminated interfering nucleotides without removing inositol phosphates. The kinetics of production of inositol phosphates in calcium-activated erythrocytes, vasopressin-stimulated hepatocytes, and thrombin-activated platelets were analyzed. Original data on the activation of phosphoinositide phospholipase C were obtained in intact erythrocytes by direct measurement of inositol (1,4,5)P3. Data from agonist-stimulated hepatocytes and platelets were consistent with those from previous studies. In conclusion, this technique offers many advantages over the methodologies currently employed involving anion-exchange chromatography and [3H]inositol labeling: (i) 32P labeling is less expensive and more efficient than 3H labeling and can be used with all types of cells without permeabilization treatments and (ii) ion-pair HPLC gives good resolution of inositol phosphates from nucleotides with shorter retention times, and long reequilibration periods are not required.

Blood Platelets↗
PubMed1989

Ultrathin (1 nm) vertically shadowed platinum-carbon replicas for imaging individual molecules in freeze-etched biological DNA and material science metal and plastic specimens.

Single molecule resolution in beam-sensitive, uncoated, noncrystalline materials has heretofore not been possible except in thin (less than or equal to 150 A) platinum-carbon (Pt-C) replicas, which are resistant to electron beam destruction. Previously, the granularity of metal film replicas limited their resolution to greater than or equal to 20 A. This paper demonstrates that Pt-C film granularity and resolution are a function of the method of replication and other controllable factors. Low-angle 20 degrees rotary, 45 degrees unidirectional, and vertical 9.7 +/- 1 A Pt-C films deposited on mica under the same conditions were compared. Vertical replication had a 5 A granularity, the highest resolution, and evenly coated the whole surface. A 45 degrees replication had a 9.5 A granularity, a slightly poorer resolution, and a discontinuous surface coating. The use of 20 degrees rotary replication proved to be unsuitable for high-resolution imaging, with 20-25 A granularity and resolution two to three times poorer. Vertical and 45 degrees Pt-C replicas can visualize the deep-etched DNA helix and the 13.3 A 3(2) helix of pectin in a gel. The DNA double helix, the complex structures of sol-gel glasses, Immobilon filters (polyvinylidene fluoride), a polymethacrylate plastic, the metal oxide surfaces of 440c stainless steel, and aluminum are illustrated. This high-resolution vertical Pt-C replica technique can image in the context of solutions, gels, or solids, single molecular chains 3-7 A wide, their associations, and their conformation. Included in the present article are first time descriptions for removing replicas from metals and plastics and for making high-magnification photographic prints of normal contrast using a reversal rephotographic process.

Carbon↗
PubMed1999

Extended resolution fluorescence microscopy.

Fluorescence microscopy is an essential tool of modern biology, but, like all forms of optical imaging, it is subject to physical limits on its resolving power. In recent years, several exciting techniques have been introduced to exceed these limits, including standing wave microscopy, 4Pi confocal microscopy, I5M and structured illumination microscopy. Several such techniques have been definitively demonstrated for the first time during the past year.

Animals↗
PubMed2000

Structural biology with carbon nanotube AFM probes.

Carbon nanotubes represent ideal probes for high-resolution structural and chemical imaging of biomolecules with atomic force microscopy. Recent advances in fabrication of carbon nanotube probes with sub-nanometer radii promise to yield unique insights into the structure, dynamics and function of biological macromolecules and complexes.

Animals↗
PubMed2006

In vivo cell biology: following the zebrafish trend.

A deeper understanding of the mechanisms of cell behavior is essential if we want to comprehend how an organism develops and functions. Changes in cellular processes, including the orientation of cell divisions, cell shape, polarity, differentiation and migration, account for tissue rearrangements during development and homeostasis. The in vivo relevance of in vitro findings is being constantly debated and the need for in vivo systems becoming more pressing. The zebrafish (Danio rerio) might become the vertebrate system of choice for a wide spectrum of biological questions that need to be investigated in vivo at cellular and subcellular resolutions. Here, we discuss some recent studies in which the zebrafish was used to gain insight into cell-biological mechanisms. Although this model system has been predominantly appreciated for its amenability to forward genetics, current advances in imaging technology and an increasing number of transgenic lines are bringing it closer to its full potential.

Animals↗
PubMedDate not supplied

Gas chromatography-high-resolution mass spectrometric method for determination of methamphetamine and its major metabolite amphetamine in human hair.

Gas chromatography-high-resolution mass spectrometric (GC-HRMS) method is presented for the qualitative and quantitative analysis of methamphetamine (MA) and its major metabolite, amphetamine (AMP), in human hair. The method procedure involves decontamination of hair with distilled water and acetone, acidic hydrolysis and extraction in the presence of the internal standard, and GC-HRMS selective ion monitoring (SIM) analysis. The limits of detection (LOD) were 9 pg/mg for MA and 21 pg/mg for AMP using a 30-mg hair sample, and the SIM responses were linear with coefficients of correlation ranged from 0.9998 to 0.9999. The recoveries were found to be 91.1-92.3%. By using HRMS (resolution of 5000), detection sensitivity is improved because of the elimination of the biological background, and the LODs for MA and AMP were 2.4-4.4 times lower than those of low-resolution MS. The GC-HRMS method was successfully applied to the analysis of cosmetically treated hair, which is difficult to analyze with the conventional method.

Amphetamine↗
PubMed2002

Computer simulations and neutron reflectivity of proteins at interfaces.

Computer simulations in conjunction with neutron reflectivity is an excellent combination for the study of biological materials at solid-liquid interfaces: Both techniques have excellent resolution levels (Angströms) and they are mature. A stronger interaction between physicists and biologists will allow the use of these two approaches in topics of biological-biomedical interest.

Adsorption↗
PubMed2003

Rad50/SMC proteins and ABC transporters: unifying concepts from high-resolution structures.

ATP-binding cassette (ABC)-type ATPases are chemo-mechanical engines for diverse biological pathways. ABC ATPase domains act not only in ABC transporters but also in DNA mismatch, nucleotide excision and double-strand break repair enzymes, as well as in chromosome segregation. Atomic-resolution crystal structures suggest molecular mechanisms for ABC ATPases and reveal surprisingly significant mechanistic and architectural conservation. This emerging unified structural biochemistry provides general medical and biological insights into how ABC proteins function as chemo-mechanical devices. ATP binding by the signature and Q-loop motifs drives the conformations of substrate-specific domains to accomplish diverse functions in transmembrane transport and DNA repair.

ATP-Binding Cassette Transporters↗
PubMed1999

Biological effects and safety issues related to long-chain polyunsaturated fatty acids in infants.

The purpose of this workshop at the American Oil Chemists' Society Symposium, "PUFA in Infant Nutrition: Consensus and Controversies," was to enumerate the safety issues raised by the prospect of supplementing infant formulas with long-chain polyunsaturated fatty acids (LC-PUFA), to evaluate the evidence that these concerns are problematical, or theoretically problematical, and to identify the safety issues most in need of resolution. This was approached by reviewing briefly the known biological effects of LC-PUFA and how these effects might give rise to concerns about safety of LC-PUFA as components of infant formulas. Some of these issues were then discussed in more detail by invited participants, all of whom had submitted abstracts concerning the issue discussed. The pertinent aspects of all issues discussed during the workshop are summarized. In addition, since the symposium was held over 2 yr ago, an addendum summarizing additional data reported since the symposium that either support or refute issues discussed during the workshop also is included.

Fatty Acids, Unsaturated↗
PubMed2006

Biological applications of scanning electrochemical microscopy: chemical imaging of single living cells and beyond.

Recent applications of scanning electrochemical microscopy (SECM) to studies of single biological cells are reviewed. This scanning probe microscopic technique allows the imaging of an individual cell on the basis of not only its surface topography but also such cellular activities as photosynthesis, respiration, electron transfer, single vesicular exocytosis and membrane transport. The operational principles of SECM are also introduced in the context of these biological applications. Recent progress in techniques for high-resolution SECM imaging are also reviewed. Future directions, such as single-channel detection by SECM, high-resolution imaging with nanometer-sized probes, and combined SECM techniques for multidimensional imaging are also discussed.

Animals↗
PubMed1979

Biological X-ray microanalysis.

By means of X-ray microanalysis it is now practical to detect approximately 10(-19) g of an element in a static-probe analysis within an ultrathin section, with analytical spatial resolution in the range 20--30 nm. The main difficulties for biological microanalysis are connected not with sensitivity but with specimen preparation and beam damage. Careful cryopreparation, beginning with the quench-freezing of a small block of tissue, is essential even for determining the storage sites, or sites of binding in vivo, of physiologically active elements. In frozen-dried or frozen-hydrated sections of quench-frozen tissue, it is now possible to measure local mass fractions of diffusible as well as of bound elements.

Biology↗
PubMed2006

Low-frequency normal modes that describe allosteric transitions in biological nanomachines are robust to sequence variations.

By representing the high-resolution crystal structures of a number of enzymes using the elastic network model, it has been shown that only a few low-frequency normal modes are needed to describe the large-scale domain movements that are triggered by ligand binding. Here we explore a link between the nearly invariant nature of the modes that describe functional dynamics at the mesoscopic level and the large evolutionary sequence variations at the residue level. By using a structural perturbation method (SPM), which probes the residue-specific response to perturbations (or mutations), we identify a sparse network of strongly conserved residues that transmit allosteric signals in three structurally unrelated biological nanomachines, namely, DNA polymerase, myosin motor, and the Escherichia coli chaperonin. Based on the response of every mode to perturbations, which are generated by interchanging specific sequence pairs in a multiple sequence alignment, we show that the functionally relevant low-frequency modes are most robust to sequence variations. Our work shows that robustness of dynamical modes at the mesoscopic level is encoded in the structure through a sparse network of residues that transmit allosteric signals.

Allosteric Regulation↗
PubMedDate not supplied

Metal complexes of chiral pentaazacrowns as conformational templates for beta-turn recognition.

Examples of reverse turns as recognition motifs in biological systems can be found in high-resolution crystal structures of antibody-peptide complexes. Development of peptidomimetics is often based on replacing the amide backbone of peptides by sugar rings, steroids, benzodiazepines, or other hetero- and carbocycles. In this approach, the chemical scaffold of the peptide backbone can be replaced while retaining activity as long as the pharmacophoric groups of the peptide side chains stay in relatively the same place; in other words, similar functional groups must overlap in space for interaction with critical receptor sites. This study evaluates the potential of metal complexes of chiral pentaazacrowns (PAC) derived by reduction of cyclic pentapeptides as beta-turn mimetics. Due to the limited flexibility of the pendant chiral side groups in these metal complexes, one can potentially elicit information about the receptor-bound conformation from their binding affinities. 11 PAC crystal structures with different substitution patterns complexed with 3 different metals (Mn, Fe, Cd) as a prototypical database of potential side-chain orientations. Complexation with different metals induces subtle differences in the conformations of a particular azacrown scaffold. The lack of parameterization of transition metals for force field calculations precludes a thorough theoretical study. Thus, this study utilizes a simple geometrical comparison between the experimental data for crystalline PAC complexes and the side-chain orientations seen in classic beta-turns. The FOUNDATION program was used to overlap the Calpha-Cbeta vectors of the corresponding ideal beta-turn side-chains to all possible leaving groups of the PAC complexes. When comparing the relative orientations of the chiral side chains, a strong overlap of the bonds (between about 0.1 A to about 0.5 A RMS for 3 residues and up to about 1 A RMS for 4 residues) was observed for many of the molecules. Such metal complexes may lack complete peptidomimetic activity due to the lack of spatial overlap of all four side-chain residues, however, if only three peptide side chains are needed for receptor recognition and/or binding, the metal complexes should show biological activity.

Computer Simulation↗
PubMed2004

A system for acquiring simultaneous electron energy-loss and X-ray spectrum-images.

A compositional imaging system based on simultaneous scanning electron energy-loss spectroscopy (EELS) and energy-dispersive X-ray spectroscopy (EDS) was developed. This system utilizes the combined power of EELS and EDS for quantitative compositional imaging at nanometre resolution. The system is particularly suitable for, but not limited to, biological research, as it simultaneously provides sensitive maps of an element such as Ca or P from EELS and of many other elements from EDS. Degradation of resolution by specimen drift is prevented by correcting for drift during data acquisition, using image cross-correlation. Several advanced features are implemented for real-time and/or off-line quantitative analysis, and the performance of the system is illustrated with practical applications to compositional imaging of cardiac muscle.

Animals↗
PubMed1978

A new organ spectrophotometer for sensitive dual-wavelength absorbance measurement and spectral scanning of intact perfused organs.

1) A new spectrophotometer was designed and constructed for application in high sensitivity dual-wavelength absorbance and fluorescence measurement and spectral scanning (non corrected) from intact perfused organs, combining advantages of other instruments described in the literature. 2) The time-sharing principle was applied to gain high stability. All optical and electronic components except the light paths of the wavelength modulation system are common to both wave-lengths. For this purpose the logarithmic stage was introduced before demodulation. Stability is about 0.001 A/h and noise about 0.001 A. 3) The performance of the instrument with a biological object, the isolated perfused rat liver, is demonstrated in the dual-wavelength mode and in the spectral scanning mode. Limitations in stability and in time resolution in such an application result from the properties of the biological object, not from the instrument.

Aminopyrine↗
PubMed1980

Imaging unstained proteoglycan aggregates by soft x-ray contact microscopy.

Soft X-ray contact microscopy is a relatively new form of ultrastructural imaging, having better than 6 nm resolution and being uniquely well suited for the examination of fragile, unstained biological specimens. The biological specimen placed on a layer of photoresist and exposed to soft X-rays (1-10 nm lambda) of a specific wavelength or broad band. After X-ray exposure, the specimen is removed from the photoresist and the latter chemically developed. When the developed replica is examined by high resolution scanning electron microscopy, the fine structure of the original biological specimen is faithfully reproduced. Since the soft X-ray replica is initially formed due to the differential absorption of the incident X-rays by the biological specimen, the resultant contact replica also reveals information about the elemental composition of the sample. This paper presents our application of this new technique for the study of the proteoglycans, the complex polyanionic macromolecules comprising the gel phase in the matrix of mammalian cartilage.

Animals↗
PubMed2003

High-resolution optical Doppler tomography for in vitro and in vivo fluid flow dynamics.

BACKGROUND: The objective of our research was to use a noninvasive tomographic imaging technique with high spatial resolution (2-15 microm) to characterize and monitor fluid flow and the microvasculature in highly scattering biological tissues at user-specified discrete locations. METHODS: The technique of optical Doppler tomography (ODT) combines laser Doppler flowmetry (LDF) with optical coherence tomography to obtain high-resolution tomographic velocity and structural images of static and moving constituents in highly scattering biological tissues. We present ODT structural and velocity images using in vitro turbid samples of a circular conduit infused with a suspension of polymer microspheres. At a thin rectangular cross-section of the conduit, the Intralipid flow was measured. Blood flow velocity was measured in vivo in the ear of rodent skin. RESULTS: In first model, the ODT velocity images demonstrated beads near the center of the conduit moving faster than those near the circular wall. In the second model, the ODT velocity images indicated that laminar flow was fastest along the central axis of the conduit. Blood flow in 2 small veins with diameters of 70 and 40 microm, respectively, and an artery with diameter of 25 microm, was clearly identified in a rodent model. CONCLUSION: In our preliminary in vitro and in vivo studies on turbid samples and model vasculatures, we determined that the application of ODT to characterize and image blood flow with high spatial resolution at discrete user-specified locations in highly scattering biological tissues is feasible.

Animals↗
PubMed1988

Digitization of electron micrographs: a comparison of three different types of scanners.

Some aspects of digitization of electron micrographs have been investigated. The performances of a flat-bed, a rotating drum, and a diode array scanner have been evaluated. Estimates have been achieved for resolution, mechanical and optical stability, and optical density response. It is concluded that for routine transmission electron microscopy of, for example, negatively stained biologic specimens, a diode array scanner produces data good enough to obtain resolutions at a level normally expected. High speed is the major advantage with this type of equipment. However, for high-resolution work it is necessary to use a conventional scanner with a relatively slow scan speed.

Analog-Digital Conversion↗