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At least 721 records · Page 40Linked to original sources
PubMed2002

ORC and the intra-S-phase checkpoint: a threshold regulates Rad53p activation in S phase.

The intra-S-phase checkpoint in yeast responds to stalled replication forks by activating the ATM-like kinase Mec1 and the CHK2-related kinase Rad53, which in turn inhibit spindle elongation and late origin firing and lead to a stabilization of DNA polymerases at arrested forks. A mutation that destabilizes the second subunit of the Origin Recognition Complex, orc2-1, reduces the number of functional replication forks by 30% and severely compromises the activation of Rad53 by replication stress or DNA damage in S phase. We show that the restoration of the checkpoint response correlates in a dose-dependent manner with the restoration of pre-replication complex formation in G1. Other forms of DNA damage can compensate for the reduced level of fork-dependent signal in the orc2-1 mutant, yet even in wild-type cells, the amount of damage required for Rad53 activation is higher in S phase than in G2. Our data suggest the existence of an S-phase-specific threshold that may be necessary to allow cells to tolerate damage-like DNA structures present at normal replication forks.

Cell Cycle Proteins↗
PubMed1999

A fission yeast gene, him1(+)/dfp1(+), encoding a regulatory subunit for Hsk1 kinase, plays essential roles in S-phase initiation as well as in S-phase checkpoint control and recovery from DNA damage.

Saccharomyces cerevisiae CDC7 encodes a serine/threonine kinase required for G(1)/S transition, and its related kinases are present in fission yeast as well as in higher eukaryotes, including humans. Kinase activity of Cdc7 protein depends on the regulatory subunit, Dbf4, which also interacts with replication origins. We have identified him1(+) from two-hybrid screening with Hsk1, a fission yeast homologue of Cdc7 kinase, and showed that it encodes a regulatory subunit of Hsk1. Him1, identical to Dfp1, previously identified as an associated molecule of Hsk1, binds to Hsk1 and stimulates its kinase activity, which phosphorylates both catalytic and regulatory subunits as well as recombinant MCM2 protein in vitro. him1(+) is essential for DNA replication in fission yeast cells, and its transcription is cell cycle regulated, increasing at middle M to late G(1). The protein level is low at START in G(1), increases at the G(1)/S boundary, and is maintained at a high level throughout S phase. Him1 protein is hyperphosphorylated at G(1)/S through S during the cell cycle as well as in response to early S-phase arrest induced by nucleotide deprivation. Deletion of one of the motifs conserved in regulatory subunits for Cdc7-related kinases as well as alanine substitution of three serine and threonine residues present in the same motif resulted in a defect in checkpoint regulation normally induced by hydroxyurea treatment. The alanine mutant also showed growth retardation after UV irradiation and the addition of methylmethane sulfonate. In keeping with this result, a database search indicates that him1(+) is identical to rad35(+). Our results reveal a novel function of the Cdc7/Dbf4-related kinase complex in S-phase checkpoint control as well as in growth recovery from DNA damage in addition to its predicted essential function in S-phase initiation.

Amino Acid Sequence↗
PubMed1997

Increased interleukin-1 and interleukin-1 receptor antagonist levels in cervical mucus in the ovulatory phase in comparison with the follicular phase.

Interleukin-1 (IL-1) receptor antagonist (IL-1ra) levels in the cervical mucus of women in the ovulatory phase are significantly higher than those in the follicular phase. IL-1 titers of women in the ovulatory phase are also significantly higher than those in the follicular phase. A positive correlation between IL-1ra and IL-1 levels in the cervical mucus was observed. Immunohistochemistry using an anti-IL-1ra monoclonal antibody revealed positive staining in the epithelial cells of the endocervix. These results suggest that IL-1ra from cervical epithelial cells protects the reproductive system from the toxicity of IL-1 produced in the endocervix.

Adult↗
PubMed1991

Immunomodulation of the induction phase of lymphokine-activated killer activity by acute phase proteins.

Effective treatment of head and neck cancer with biologic response modifiers may be benefitted by an understanding of in vivo factors capable of modulating the lymphokine-activated killer (LAK) cell phenomenon. Eighteen patients with squamous cell carcinoma of the head and neck were studied. Killer cells from each patient, activated by recombinant interleukin-2 (10 U/ml), were induced in either complete medium alone or complete medium plus 10% autologous serum solution and analyzed. Cytotoxicity against both K562 and squamous cell carcinoma (MDA686-Ln) cell lines was determined by use of standard chromium-release assays. The immunomodulatory capacity of serum was correlated with levels of various acute phase proteins. Autologous serum significantly inhibited the induction phase of the LAK phenomenon in 61% of patients and stimulated it in 22%. No patients with early stage I or II disease had significant inhibition of induction. No direct correlation between inhibition and serum acute phase protein levels were seen. An inverse relationship was seen between the C3 component of complement and induction inhibition (r = -0.6). These findings suggest that advances of in vivo immunomodulatory therapy will require elucidation of mechanisms of serologic inhibition of the induction phase of the LAK phenomenon. Such studies may lead to serologic modification to enhance treatment efficacy of biologic response modifiers.

Acute-Phase Proteins↗
PubMed2005

Spectral-domain optical coherence phase microscopy for quantitative phase-contrast imaging.

We describe a novel microscopy technique for quantitative phase-contrast imaging of a transparent specimen. The technique is based on depth-resolved phase information provided by common path spectral-domain optical coherence tomography and can measure minute phase variations caused by changes in refractive index and thickness inside the specimen. We demonstrate subnanometer level path-length sensitivity and present images obtained on reflection from a known phase object and human epithelial cheek cells.

Cells, Cultured↗
PubMed1999

[A novel solid phase coating of solid-phase microextraction prepared with sol-gel technology and its applications].

In this paper, the recent development and applications of solid-phase microextraction (SPME) are summed up. A sol-gel method was applied for the preparation of solid phase coating in SPME. The exposed outer surface was coated with hydroxy-terminated poly (dimethylsiloxane). The characteristics of this solid phase were evaluated. The coating possesses higher thermal stability, and shorter extraction and desorption time. This solid phase appears to have strong affinity to both polar compounds and non-polar compounds. The scanning electron micrograph of the coated surface presents a porous structure. In the analyses of the environmental samples, ideal results were also obtained.

Animals↗
PubMed1995

High D-glucose stimulates the cell cycle from the G1 to the S and M phases, but has no competent effect on the G0 phase, in vascular smooth muscle cells.

The effects of high (28mM) D-glucose (HG) on the cell cycle progression were investigated in rat aorta vascular smooth muscle cells (VSMCs) in primary culture, using an immunocytochemical analysis of cell-cycle-specific nuclear antigens. HG had no effect on the cell cycle of the serum-deprived G0 cells, whereas platelet-derived growth factor (PDGF) stimulated the entry of the G0 cells to the G1 phase without a further progression to the S and M phases. HG, but neither mannitol nor L-glucose, stimulated the progression of the PDGF-pretreated G1 cells to the S and M phases, which was blocked by calphostin-C, a protein kinase C (PKC) blocker. HG did not affect the cytosolic Ca2+ concentration ([Ca2+]i). These data suggest that HG has no competent effect on the G0 cells and acts as a progression growth factor (to stimulate the cell cycle from the G1 to the S/M) in VSMCs through the mechanism, which may be insensitive to [Ca2+]i and mediated by PKC.

Animals↗
PubMed2006

Estrogen accelerates G1 to S phase transition and induces a G2/M phase-predominant apoptosis in synthetic vascular smooth muscle cells.

OBJECTIVE: To investigate the mechanisms underlying the vascular-protective effects of estrogen. METHODS: The synthetic (subcultured for 3-4 passages) rat vascular smooth muscle cells were exposed to gradient concentrations (10(-10)-10(-5) M) of 17beta-estradiol. The growth, cell cycle progression and apoptosis of the cells, and the related proteins including Cyclin D1, Cdk4, p38, Bax and Bcl-2 were analyzed in MTT, flow cytometry, ELISA or Western blot. RESULTS: 17beta-estradiol in the physiological concentrations (10(-10)-10(-8) M) promoted the smooth muscle cell growth in a concentration-dependent manner, accelerated transition of the cells from G1 to S phases, and up-regulated expressions of Cyclin D1 and Cdk4. Meanwhile, the hormone (10(-9)-10(-7) M) triggered a G2/M phase-predominant apoptosis of the cells in a concentration- and time-dependent manner, which was accompanied by increased phosphorylation of p38 and expression of Bax. CONCLUSIONS: The effect of estrogen on the synthetic vascular smooth muscle cell is dual. It promotes proliferation of the cells by accelerating their G1/S phase transition via up-regulating Cyclin D1 and Cdk4; and on the other hand, it induces apoptosis of the proliferating cells by up-regulating Bax through p38-MAPK pathway.

Analysis of Variance↗
PubMed2000

HPLC enantiomeric resolution of novel aromatase inhibitors on cellulose- and amylose-based chiral stationary phases under reversed phase mode.

The chiral resolution of seven aromatase inhibitors (four triazole derivatives (Ia, Ib, Ic, and Id) and three tetrazole derivatives (IIa, IIb, and IIc)) was achieved on Chiralcel OJ-R [cellulose tris (4-methyl benzoate)], Chiralcel OD-RH [cellulose tris (3,5-dimethylphenyl carbamate)], and Chiralpak AD-RH [amylose tris (3,5-dimethylphenyl carbamate)] chiral stationary phases. The mobile phases used were A: 2-PrOH-MeCN (90:10, v/v); B: 2-PrOH-MeCN (50:50, v/v); C: MeCN-H(2)O (50:50, v/v); D: MeCN-H(2)O (80:20, v/v); and E: MeCN-H(2)O (95:05, v/v). The flow rate was 0.5 mL/min for all the mobile phases. The resolution capability of these chiral stationary phases were in the order Chiralpak AD-RH > Chiralcel OD-RH > Chiralcel OJ-R. The values of alpha and Rs of the resolved enantiomers of the aromatase inhibitors varied from 1.02-5.63 and 1. 12-6.72, respectively.

Amylose↗
PubMed2001

High performance liquid chromatography analysis of 9-(2',3'-dideoxy-2'beta-fluoro-D-threo-penta furanosyl) adenine and its metabolite in human plasma using solid-phase extraction on a polyfluorinated reversed stationary phase.

A quick and sensitive reversed-phase HPLC method has been developed for the analysis of 2'-beta -fluoro-2',3'-dideoxy adenosine (F-ddA), the acid-stable anti-AIDS drug, and its metabolite 2'-fluoro-2',3'-dideoxy inosine (F-ddI) in human plasma using polyfluorinated stationary phase column (Fluo fix, 15 cm, 4.0 mm i.d., 5 microm particle size). The mobile phase consisted of ammonium phosphate buffer solution (10 mM) adjusted with phosphoric acid 85% to pH 6.8:dimethyl formamide (97:3, v/v). F-ddA and F-ddI were monitored by UV-visible detector at 258 and 247 nm, respectively. The recoveries of F-ddA and F-ddI from plasma using a C(18) solid-phase extraction cartridge were 99.2% and 99.7%, respectively.

Anti-HIV Agents↗
PubMed2004

Chiral analysis of butaclamol enantiomers in human plasma by HPLC using a macrocyclic antibiotic (vancomycin) chiral stationary phase and solid phase extraction.

An enantioseparation of the antipsychotic drug butaclamol in human plasma by high-performance liquid chromatography (HPLC) with solid phase extraction is presented. The separation was achieved on the vancomycin macrocyclic antibiotic chiral stationary phase (CSP) Chirobiotic V with a polar ionic mobile phase (PIM) consisting of methanol : glacial acetic acid : triethylamine (100:0.2:0.05, v/v/v) at a flow rate of 0.5 ml/min. The detection wavelength was 262 nm. Bond Elut C18 solid phase extraction cartridges were used in the sample preparation of butaclamol samples from plasma. The method was validated over the range of 100-3,000 ng/ml for each enantiomer concentration (R(2) > 0.999). Recoveries for (+)- and (-)-butaclamol were in the range of 94-104% at the 300-2,500 ng/ml level. The method proved to be precise (within-run precision ranged from 1.1-2.6% and between-run precision ranged from 1.9-3.2%) and accurate (within-run accuracies ranged from 1.5-5.8% and between-run accuracies ranged from 2.7-7.7%). The limit of quantitation (LOQ) and limit of detection (LOD) for each enantiomer in human plasma were 100 ng/ml and 50 ng/ml, respectively.

Anti-Bacterial Agents↗
PubMed2003

Quantum control of gas-phase and liquid-phase femtochemistry.

Active control of chemical reactions on a microscopic (molecular) level, that is, the selective breaking or making of chemical bonds, is an old dream. However, conventional control agents used in chemical synthesis are macroscopic variables such as temperature, pressure or concentration, which gives no direct access to the quantum-mechanical reaction pathway. In quantum control, by contrast, molecular dynamics are guided with specifically designed light fields. Thus it is possible to efficiently and selectively reach user-defined reaction channels. In the last years, experimental techniques were developed by which many breakthroughs in this field were achieved. Femtosecond laser pulses are manipulated in so-called pulse shapers to generate electric field profiles which are specifically adapted to a given quantum system and control objective. The search for optimal fields is guided by an automated learning loop, which employs direct feedback from experimental output. Thereby quantum control over gas-phase as well as liquid-phase femtochemical processes has become possible. In this review, we first discuss the theoretical and experimental background for many of the recent experiments treated in the literature. Examples from our own research are then used to illustrate several fundamental and practical aspects in gas-phase as well as liquid-phase quantum control. Some additional technological applications and developments are also described, such as the automated optimization of the output from commercial femtosecond laser systems, or the control over the polarization state of light on an ultrashort timescale. The increasing number of successful implementations of adaptive learning techniques points at the great versatility of computer-guided optimization methods. The general approach to active control of light-matter interaction has also applications in many other areas of modern physics and related disciplines.

Journal Article↗
PubMed2005

Capillary electrochromatographic separation of enantiomers under aqueous mobile phases on a covalently bonded cellulose derivative chiral stationary phase.

A chemically bonded cellulose tris(3,5-dimethylphenylcarbamate) chiral stationary phase (CSP) was prepared by a radical polymerization reaction. The prepared CSP was packed into fused-silica capillaries with inner diameter of 75 microm to perform enantiomer separations in CEC. The electrochromatographic behavior of the CSP was investigated. On the prepared CSP, high EOF could be generated under acidic mobile phases, which represented an advantage for the separation of acidic enantiomers. Several neutral, acidic, and basic enantiomers were resolved on the prepared CSP under aqueous mobile phases. The column efficiencies were between 20,000 and 100,000 plates/m, which were much higher than those of HPLC. In addition, it was observed that the separation of some enantiomers benefited from the adoption of THF as mobile phase modifier.

Cellulose↗
PubMed1984

Histone H4 gene is transcribed in S phase but also late in G(2) phase in Physarum polycephalum.

The myxomycete Physarum polycephalum contains two types of H4 histone genes. Southern blotting of restriction endonuclease fragments of P. polycephalum DNA and hybridization to a cloned probe labelled by nick-translation indicate that there are only one or two copies of each H4 gene per haploid genome. A cloned homologous genomic probe was used to study the cellular abundance of H4 mRNA during the cell cycle. We report that the H4 mRNA is not only transcribed in S phase as previously described for other organisms but that transcription of the H4 gene also occurs at the end of G(2) phase. Since no translation of the histone messenger was observed in G(2) phase this suggests that the histone mRNA synthesized in G(2) constitutes a pool of molecules in anticipation of the next S phase.

Journal Article↗
PubMed2005

Subtraction of in-phase and opposed-phase images in dynamic MR mammography.

PURPOSE: To develop and to evaluate an advanced image acquisition and analysis method for collecting T(1)-weighted dynamic 3D MR mammography data sets by using a combined in-phase (IP) and opposed-phase (OP) imaging procedure. MATERIALS AND METHODS: 3D MR mammography data sets were acquired by applying an interleaved gradient-echo OP and IP imaging sequence during administration of contrast agent. A phantom data set, two volunteer breast data sets, and six patient breast data sets were recorded. Subtraction of dynamic in-phase magnitude images was performed for clinical assessment. In addition, the magnitude subtraction (SIPOP) as well as the complex subtraction (cSIPOP) of the IP and OP magnitude and phase images were considered. RESULTS: The detection of small lesions, lesion boundaries, and tumor offshoots in fatty tissue was improved by the subtraction of IP and OP images without the risk of signal cancellation due to partial volume effects. CONCLUSION: Dynamic MR mammography acquisition of IP and OP images in combination with appropriate data processing yields important supplementary information that can support routinely applied diagnostics of breast lesions that are fully embedded in fatty tissue by only marginally increasing acquisition time.

Aged↗
PubMed1994

Reconstructions of phase contrast, phased array multicoil data.

We present a reconstruction method for phased array multicoil data that is compatible with phase contrast MR angiography. The proposed algorithm can produce either complex difference or phase difference angiograms. Directional flow and quantitative information are preserved with the phase difference reconstruction. The proposed method is computationally efficient and avoids intercoil cancellation errors near the velocity aliasing boundary. Feasibility of the method is demonstrated on human scans.

Algorithms↗
PubMed1991

Differential control of in-phase and anti-phase coupling of rhythmic movements of ipsilateral hand and foot.

Rhythmic flexion-extensions of ipsilateral hand and foot are easily performed ("easy" association) when the two segments are moved in phase (isodirectionally), whereas great care and attention are required ("difficult" association) to move them in phase opposition. We searched for features distinguishing the two types of coupling by analyzing, on ten subjects: 1) the frequency limit in each association; and, 2) if coupling is modified by inertial or elastic loading of the hand. 1) Subjects were asked to oscillate hand and foot at various paced frequencies, in the easy or in the difficult association for one minute at least. In the easy coupling, the task was performed up to 2.0-2.5 Hz, the duration being thereafter shortened by muscular fatigue. In the difficult coupling when the frequency was increased above 0.7-1.7 Hz, the performance rapidly shortened, not because of fatigue but because of an inevitable reversal to the in-phase movement. The frequency-duration curve always followed a similar decay, although it covered different frequency ranges in the various subjects. 2) The effect of charging the hand with inertial or elastic loads was studied at the subject's preferred frequency, chosen when the hand was unloaded. Without loading, in the easy association the hand cycle slightly lagged the foot cycle while in the difficult one an almost perfect phase opposition was maintained.(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗
PubMedDate not supplied

Identification of phase I and phase II metabolites of Guanfu base A hydrochloride in human urine.

Guanfu base A is a novel arrhythmic drug candidate isolated from the tuber of a traditional Chinese herb. Phase I and Phase II metabolites of Guanfu base A (GFA) Hydrochloride were studied in human urine by means of liquid chromatography mass spectrometry (LC/MSD) and tandem mass spectrometry (MS/MS). For phase I metabolites, Guanfu base I (GFI) was separated by HPLC and identified by comparison with authentic reference for their retention times, molecular ion peaks, fragment ions, and UV spectra. GFA oxide was also indicated to exist in human urine. For phase II metabolites, after human urine was treated either with glucuronidase or sulfatase, GFA occured in the chromatograms. It was suggested that there were GFA glucuronide and GFA sulfate in human urine. Further more, positive molecular ions, m/z 606 and m/z 510, of the two conjugates were detected in human urine by LC/MSD. In addition, characteristic ion of m/z 606 was identified as the precursor ion of m/z 177 [Glucuronic acid+H]+ by using MS/MS. Characteristic ion of m/z 430 [GFA+H]+ was also identified as a product ion of m/z 606 [GFA glucuronide+H]+. It was concluded that there were GFI. GFA oxide, GFA glucuronide and GFA sulfate in human urine.

Adult↗