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Articles 361 - 390 of 397

Full-Text Articles in Chemistry

Rnase L Mediates Transient Control Of The Interferon Response Through Modulation Of The Double-Stranded Rna-Dependent Protein Kinase Pkr, Khalid S.A. Khabar, Yunus M. Siddiqui, Fahad Al-Zoghaibi, Latifa Al-Haj, Mohammed Dhalla, Aimin Zhou, Beihua Dong, Mark Whitmore, Jayashree Paranjape, Mohammed N. Al-Ahdal, Futwan Al-Mohanna, Bryan R.G. Williams, Robert H. Silverman May 2003

Rnase L Mediates Transient Control Of The Interferon Response Through Modulation Of The Double-Stranded Rna-Dependent Protein Kinase Pkr, Khalid S.A. Khabar, Yunus M. Siddiqui, Fahad Al-Zoghaibi, Latifa Al-Haj, Mohammed Dhalla, Aimin Zhou, Beihua Dong, Mark Whitmore, Jayashree Paranjape, Mohammed N. Al-Ahdal, Futwan Al-Mohanna, Bryan R.G. Williams, Robert H. Silverman

Chemistry Faculty Publications

The transient control of diverse biological responses that occurs in response to varied forms of stress is often a highly regulated process. During the interferon (IFN) response, translational repression due to phosphorylation of eukaryotic initiation factor 2α, eIF2α, by the double-stranded RNA-dependent protein kinase, PKR, constitutes a means of inhibiting viral replication. Here we show that the transient nature of the IFN response against acute viral infections is regulated, at least in part, by RNase L. During the IFN antiviral response in RNase L-null cells, PKR mRNA stability was enhanced, PKR induction was increased, and the phosphorylated form of eIF2α …

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Evaluating The Effects Of Enhanced Processivity And Metal Ions On Translesion Dna Replication Catalyzed By The Bacteriophage T4 Dna Polymerase, Edmunds Z. Reineks, Anthony J. Berdis May 2003

Evaluating The Effects Of Enhanced Processivity And Metal Ions On Translesion Dna Replication Catalyzed By The Bacteriophage T4 Dna Polymerase, Edmunds Z. Reineks, Anthony J. Berdis

Chemistry Faculty Publications

The fidelity of DNA replication is achieved in a multiplicative process encompassing nucleobase selection and insertion, removal of misinserted nucleotides by exonuclease activity, and enzyme dissociation from primer/templates that are misaligned due to mispairing. In this study, we have evaluated the effect of altering these kinetic processes on the dynamics of translesion DNA replication using the bacteriophage T4 replication apparatus as a model system. The effect of enhancing the processivity of the T4 DNA polymerase, gp43, on translesion DNA replication was evaluated using a defined in vitro assay system. While the T4 replicase (gp43 in complex with gp45) can perform …

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The Solvent Boundary Potential: A New Approach For Computer Simulation Of Large Systems, Valentin Gogonea Mar 2003

The Solvent Boundary Potential: A New Approach For Computer Simulation Of Large Systems, Valentin Gogonea

Chemistry Faculty Publications

The paper presents the theoretical framework for the development of a new solvent boundary method for computer simulations and its possible application to the simulation of nitric oxide synthase. Different approaches for the construction of a solvent boundary potential are reviewed and their strengths and weaknesses are discussed. A new solvent boundary potential is proposed which combines the mean field force approximation with the Green's function approach for treating long-range electrostatic interactions, and introduces a novel strategy to treat electrostriction effects due to ions crossing the solvent boundary. Finally, a series of computational tests are devised in order to assess …

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Measurement Of The Anti-Cancer Agent Gemcitabine In Human Plasma By High-Performance Liquid Chromatography, Bruce Keith, Yan Xu, Jean L. Grem Feb 2003

Measurement Of The Anti-Cancer Agent Gemcitabine In Human Plasma By High-Performance Liquid Chromatography, Bruce Keith, Yan Xu, Jean L. Grem

Chemistry Faculty Publications

A reversed-phase HPLC assay has been developed to determine the concentration of the anti-metabolite 2′,2′-difluorodeoxycytidine (gemcitabine, dFdC) in human plasma over the concentration range of 0.5–150 μM (0.13–39.44 μg/ml), and 2′,2′-difluorodeoxyuridine (dFdU), the deaminated, inactive metabolite, over the range of 1.0–227 μM (0.26–60 μg/ml). After the addition of 20 nmol 2′-fluorodeoxycytidine (FdC) as an internal standard, 0.5-ml samples of plasma were subjected to acetonitrile precipitation, followed by analysis using a gradient reversed-phase HPLC assay with UV detection. A Phenomenex Columbus™ C18 column, 5 μm, 150×4.6 mm, and a Waters C18, 4 μm, Nova-Pak Sentry guard column were used to achieve …

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Examination Of The Role Of The Clamp-Loader And Atp Hydrolysis In The Formation Of The Bacteriophage T4 Polymerase Holoenzyme, Michael A. Trakselis, Anthony J. Berdis, Stephen J. Benkovic Feb 2003

Examination Of The Role Of The Clamp-Loader And Atp Hydrolysis In The Formation Of The Bacteriophage T4 Polymerase Holoenzyme, Michael A. Trakselis, Anthony J. Berdis, Stephen J. Benkovic

Chemistry Faculty Publications

Transient kinetic analyses further support the role of the clamp-loader in bacteriophage T4 as a catalyst which loads the clamp onto DNA through the sequential hydrolysis of two molecules of ATP before and after addition of DNA. Additional rapid-quench and pulse-chase experiments have documented this stoichiometry. The events of ATP hydrolysis have been related to the opening/closing of the clamp protein through fluorescence resonance energy transfer (FRET). In the absence of a hydrolysable form of ATP, the distance across the subunit interface of the clamp does not increase as measured by intramolecular FRET, suggesting gp45 cannot be loaded onto DNA. …

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Synthesis And Potential Antimetastatic Activity Of Monovalent And Divalent Β-D-Galactopyranosyl-(1→4)-2-Acetamido-2-Deoxy-D-Glucopyranosides, Qin Li, Bin Su, Hui Li, Xiang Bao Meng, Meng Shen Cai, Zhong Jun Li, Rou Li Zhou, Ta Lin Suo Jan 2003

Synthesis And Potential Antimetastatic Activity Of Monovalent And Divalent Β-D-Galactopyranosyl-(1→4)-2-Acetamido-2-Deoxy-D-Glucopyranosides, Qin Li, Bin Su, Hui Li, Xiang Bao Meng, Meng Shen Cai, Zhong Jun Li, Rou Li Zhou, Ta Lin Suo

Chemistry Faculty Publications

Anomers of monovalent and divalent β-d-galactopyranosyl-(1→4)-2-acetamido-2-deoxy-d-gluco-pyranosides were synthesized under different glycosylation conditions, and evaluated for in vitro antimetastatic activity. Three compounds showed promising inhibitory effects on cancer cell attachment, spreading, migration, and invasion. Six divalent O-β-d-galactopyranosyl-(1→4)-2-acetamido-2-deoxy-d-glucopyranosides (29–34) were synthesized and their antimetastatic activities were studied.

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Liquid Chromatography–Mass Spectrometry Method For The Analysis Of The Anti-Cancer Agent Capecitabine And Its Nucleoside Metabolites In Human Plasma, Yan Xu, Jean L. Grem Jan 2003

Liquid Chromatography–Mass Spectrometry Method For The Analysis Of The Anti-Cancer Agent Capecitabine And Its Nucleoside Metabolites In Human Plasma, Yan Xu, Jean L. Grem

Chemistry Faculty Publications

A reversed-phase high-performance liquid chromatography method with electrospray ionization and mass spectral detection is described for the determination of capecitabine, 5′-deoxy-5-fluorocytidine and 5′-deoxy-5-fluorouridine in human plasma with 5-chloro-2′-deoxyuridine as the internal standard. An on-line sample clean-up procedure allows dilution of the plasma sample with the initial mobile phase. The linear dynamic range is 0.0500–10.0 μg/ml for capecitabine, and 0.0500–25.0 μg/ml for the metabolites, 5′-deoxy-5-fluorocytidine and 5′-deoxy-5-fluorouridine, respectively. This method has been used to analyze plasma samples from patients receiving capecitabine in combination with oxaliplatin.

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A Phase I And Pharmacologic Study Of Weekly Gemcitabine In Combination With Infusional 5-Fluorodeoxyuridine And Oral Calcium Leucovorin, Jean L. Grem, Mary G. Quinn, Bruce Keith, Brian P. Monahan, J. Michael Hamilton, Yan Xu, Nancy Harold, Dat Nguyen, Chris H. Takimoto, Anthony Rowedder, Janet Pang, Geraldine Morrison, Alice Chen Jan 2003

A Phase I And Pharmacologic Study Of Weekly Gemcitabine In Combination With Infusional 5-Fluorodeoxyuridine And Oral Calcium Leucovorin, Jean L. Grem, Mary G. Quinn, Bruce Keith, Brian P. Monahan, J. Michael Hamilton, Yan Xu, Nancy Harold, Dat Nguyen, Chris H. Takimoto, Anthony Rowedder, Janet Pang, Geraldine Morrison, Alice Chen

Chemistry Faculty Publications

Purpose: Since preclinical studies have shown more than additive cytotoxicity and DNA damage with the combination of gemcitabine and 5-fluoro-2′-deoxyuridine (FUDR), we studied this combination in a phase I trial. Methods: Gemcitabine alone was given in cycle 1 as a 24-h, 2-h or 1-h i.v. infusion weekly for 3 of 4 weeks; if tolerated, a 24-h i.v. infusion of FUDR was added with oral leucovorin. The cycle was aborted for grade 3 thrombocytopenia, grade 4 neutropenia, and grade 2 or worse nonhematologic toxicity. Results: During cycle 1, six of eight patients who received 150 or 100 mg/m2 over 24 h …

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Synthesis Of A Spacer-Armed Disulfated Tetrasaccharide Of Sb1a, A Carbohydrate Hapten Associated With Human Hepatocellular Carcinoma, Qin Li, Hui Li, Qing Li, Qing Hua Lou, Bin Su, Meng Shen Cai, Zhong Jun Li Nov 2002

Synthesis Of A Spacer-Armed Disulfated Tetrasaccharide Of Sb1a, A Carbohydrate Hapten Associated With Human Hepatocellular Carcinoma, Qin Li, Hui Li, Qing Li, Qing Hua Lou, Bin Su, Meng Shen Cai, Zhong Jun Li

Chemistry Faculty Publications

A disulfated tetrasaccharide fragment with a spacer arm of human hepatocellular carcinoma carbohydrate antigen SB1a, namely, 2-aminoethyl 3-O-sulfo-β-d-galactopyranosyl-(1→3)-2-acetamido-2-deoxy-β-d-galactopyranosyl-(1→4)-3-O-sulfo-β-d-galactopyranosyl-(1→4)-β-d-glucopyranoside was synthesized via a [2+1+1] block building mode. In the last coupling step toward the trisaccharide acceptor 8, benzoyl protected galactosyl bromide donor 14 was found to be much more reactive than the acetyl-protected donors. A disulfated tetrasaccharide fragment with a spacer arm of human hepatocellular carcinoma carbohydrate antigen SB1a was synthesized via a [2+1+1] block building mode.

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Rapid Determination Of Serum Melatonin By Esi–Ms–Ms With Direct Sample Injection, Shuming Yang, Xiaohui Zheng, Yan Xu, Xiang Zhou Oct 2002

Rapid Determination Of Serum Melatonin By Esi–Ms–Ms With Direct Sample Injection, Shuming Yang, Xiaohui Zheng, Yan Xu, Xiang Zhou

Chemistry Faculty Publications

This paper describes a rapid, simple and sensitive analytical method for the quantitative determination of melatonin in human serum by ESI–MS–MS with direct serum sample injection and on-line extraction. The method uses N-acetyltryptamine as the internal standard. It has high specificity and sensitivity for serum melatonin analysis. The internal calibration curve shows a wide linear range from 0.500 to 200 ng/ml with a correlation coefficient, R2>0.999. The limit of quantitation is 0.500 ng/ml and the limit of detection is 0.100 ng/ml with 10-μl sample injection. The recoveries of serum melatonin at three levels are approximately 70%. The intra-assay precision …

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Chemical Imaging Comes Of Age, John F. Turner Ii May 2002

Chemical Imaging Comes Of Age, John F. Turner Ii

Chemistry Faculty Publications

Sophisticated analysis techniques allow researchers to extract meaningful results from spectral imaging data.

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Simultaneous Determination Of Enantiomers Of Structurally Related Anticholinergic Analogs In Human Serum By Liquid Chromatography–Electrospray Ionization Mass Spectrometry With On-Line Sample Cleanup, Vladimı́R Čápka, Yan Xu Oct 2001

Simultaneous Determination Of Enantiomers Of Structurally Related Anticholinergic Analogs In Human Serum By Liquid Chromatography–Electrospray Ionization Mass Spectrometry With On-Line Sample Cleanup, Vladimı́R Čápka, Yan Xu

Chemistry Faculty Publications

Trihexyphenidyl, biperiden and procyclidine are anticholinergic drugs produced as racemates for the treatment of Parkinson’s disease. This paper describes a simple and sensitive LC–MS method for the simultaneous determination of these compounds in human serum. An on-line sample clean-up procedure was used, where serum samples were directly injected into a “restricted-access media” pre-column. After the exclusion of the serum proteins, the drug molecules were eluted to a β-cyclodextrin analytical column for chiral separation. The quantitation was done by electrospray ionization MS using diphenidol as an internal standard. The method developed has limits of detection of 1 ng/ml, at least two-orders-of-magnitude …

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Determination Of Lysophosphatidic Acids By Capillary Electrophoresis With Indirect Ultraviolet Detection, Yi Lung Chen, Yan Xu Apr 2001

Determination Of Lysophosphatidic Acids By Capillary Electrophoresis With Indirect Ultraviolet Detection, Yi Lung Chen, Yan Xu

Chemistry Faculty Publications

Lysophosphatidic acid (LPA) is the simplest form of lysophospholipid. Molecular species of LPA have been identified as the potent components in the ovarian cancer activation factor. The elevated plasma LPAs may be used as potential biomarkers for the early detection of ovarian cancer. This paper is the first report on the quantitative analysis of molecular species of LPA using capillary electrophoresis. In this work, the separation of LPAs was achieved within 14 min in an adenosine monophosphate-borate–methanol–water solution, and the measurement was accomplished by indirect UV detection. With LPA (D) as internal standard, the method had linear calibration ranges for …

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Adenosine Triphosphate-Dependent Degradation Of A Fluorescent Λ N Substrate Mimic By Lon Protease, Irene Lee, Anthony J. Berdis Apr 2001

Adenosine Triphosphate-Dependent Degradation Of A Fluorescent Λ N Substrate Mimic By Lon Protease, Irene Lee, Anthony J. Berdis

Chemistry Faculty Publications

Escherichia coli Lon exhibits a varying degree of energy requirement toward hydrolysis of different substrates. Efficient degradation of protein substrates requires the binding and hydrolysis of ATP such that the intrinsic ATPase of Lon is enhanced during protein degradation. Degradation of synthetic tetrapeptides, by contrast, is achieved solely by ATP binding with concomitant inhibition of the ATPase activity. In this study, a synthetic peptide (FRETN 89-98), containing residues 89–98 of λ N protein and a fluorescence donor (anthranilamide) and quencher (3-nitrotyrosine), has been examined for ATP-dependent degradation by E. coli and human Lon proteases. The cleavage profile of FRETN 89-98 …

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Rayleigh And Raman Scattering, David W. Ball Feb 2001

Rayleigh And Raman Scattering, David W. Ball

Chemistry Faculty Publications

Details the molecular aspect of Raman spectroscopy. Overview on the molecular absorption process; Information on Rayleigh scattering; Effects of the Raman scattering.

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Increased Severity Of Hsv-1 Keratitis And Mortality In Mice Lacking The 2–5a-Dependent Rnase L Gene, Xiaodong Zheng, Robert H. Silverman, Aimin Zhou, Tomoko Goto, Byoung Se Kwon, Herbert E. Kaufman, James M. Hill Jan 2001

Increased Severity Of Hsv-1 Keratitis And Mortality In Mice Lacking The 2–5a-Dependent Rnase L Gene, Xiaodong Zheng, Robert H. Silverman, Aimin Zhou, Tomoko Goto, Byoung Se Kwon, Herbert E. Kaufman, James M. Hill

Chemistry Faculty Publications

Purpose: The2′,5′-oligoadenylate-dependent RNase L gene functions in the interferon-inducible RNA decay pathway known as the 2–5A system. The purpose of this study was to determine whether the absence of this gene affects the pathogenesis of herpes simplex virus type 1 (HSV-1) ocular infection in the mouse. Methods: HSV-1 (strain McKrae) was applied bilaterally to unscarified corneas of RNase L–null mice and congenic controls. To evaluate the severity of herpetic keratitis, slit lamp examinations (SLE) were performed every other day for 14 days. To study corneal histology and apoptosis, HSV-1–inoculated RNase-L-null and congenic control mice, as well as mock-inoculated mice (apoptosis …

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Rnase L-Independent Specific 28s Rrna Cleavage In Murine Coronavirus-Infected Cells, Sangeeta Banerjee, Sungwhan An, Aimin Zhou, Robert H. Silverman, Shinji Makino Oct 2000

Rnase L-Independent Specific 28s Rrna Cleavage In Murine Coronavirus-Infected Cells, Sangeeta Banerjee, Sungwhan An, Aimin Zhou, Robert H. Silverman, Shinji Makino

Chemistry Faculty Publications

We characterized a novel 28S rRNA cleavage in cells infected with the murine coronavirus mouse hepatitis virus (MHV). The 28S rRNA cleavage occurred as early as 4 h postinfection (p.i.) in MHV-infected DBT cells, with the appearance of subsequent cleavage products and a decrease in the amount of intact 28S rRNA with increasing times of infection; almost all of the intact 28S rRNA disappeared by 24 h p.i. In contrast, no specific 18S rRNA cleavage was detected in infected cells. MHV-induced 28S rRNA cleavage was detected in all MHV-susceptible cell lines and all MHV strains tested. MHV replication was required …

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9-Phenyl-3,4,4a,9a-Tetrahydrotriptycene And 9-Phenyl-1,2,3,4,4a,9a-Hexahydrotriptycene, John Masnovi, Shaoming Duan, Ronald J. Baker Jan 2000

9-Phenyl-3,4,4a,9a-Tetrahydrotriptycene And 9-Phenyl-1,2,3,4,4a,9a-Hexahydrotriptycene, John Masnovi, Shaoming Duan, Ronald J. Baker

Chemistry Faculty Publications

The structure of 9-phenyl-3,4,4a,9a-tetrahydrotriptycene, C26H22, (I), exhibits regiochemistry consistent with a stepwise mechanism for its formation from photocycloaddition of 1,3- cyclohexadiene and 9-phenylanthracene. Bond distances involving the bridgehead C atoms are similar in (I) and the hydrogenated derivative, 9-phenyl-1,2,3,4,4a,9a-hexahydrotriptycene, C26H24, (II), with bonds to the quaternary-C atoms exhibiting significant elongation [1.581 (2) A Ê in (I) and 1.585 (2) A Ê in (II)]. The molecular geometry precludes significant overlap between the phenyl groups and the interannular bonds in both compounds, indicating that the origin of the bond lengthening is steric in nature.

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Activation Of P38 Mitogen-Activated Protein Kinase And C-Jun Nh2-Terminal Kinase By Double-Stranded Rna And Encephalomyocarditis Virus: Involvement Of Rnase L, Protein Kinase R, And Alternative Pathways, Mihail S. Iordanov, Jayashree M. Paranjape, Aimin Zhou, John Wong, Bryan R.G. Williams, Eliane F. Meurs, Robert H. Silverman, Bruce E. Magun Jan 2000

Activation Of P38 Mitogen-Activated Protein Kinase And C-Jun Nh2-Terminal Kinase By Double-Stranded Rna And Encephalomyocarditis Virus: Involvement Of Rnase L, Protein Kinase R, And Alternative Pathways, Mihail S. Iordanov, Jayashree M. Paranjape, Aimin Zhou, John Wong, Bryan R.G. Williams, Eliane F. Meurs, Robert H. Silverman, Bruce E. Magun

Chemistry Faculty Publications

Double-stranded RNA (dsRNA) accumulates in virus-infected mammalian cells and signals the activation of host defense pathways of the interferon system. We describe here a novel form of dsRNA-triggered signaling that leads to the stimulation of the p38 mitogen-activated protein kinase (p38 MAPK) and the c-Jun NH2-terminal kinase (JNK) and of their respective activators MKK3/6 and SEK1/MKK4. The dsRNA-dependent signaling to p38 MAPK was largely intact in cells lacking both RNase L and the dsRNA-activated protein kinase (PKR), i.e., the two best-characterized mediators of dsRNA-triggered antiviral responses. In contrast, activation of both MKK4 and JNK by dsRNA was greatly reduced in …

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Stereoselective Determination Oftrihexyphenidyl In Human Serum By Lc–Esi–Ms, Vladimı́R Čápka, Yan Xu, Yong Hong Chen Nov 1999

Stereoselective Determination Oftrihexyphenidyl In Human Serum By Lc–Esi–Ms, Vladimı́R Čápka, Yan Xu, Yong Hong Chen

Chemistry Faculty Publications

The antiparkinsonian drug trihexyphenidyl (THP) is currently manufactured and administered as a racemate. However, stereochemistry can play significant role in the drug’s pharmacokinetics, biotransformation, metabolism, interaction with cellular and tissue components and overall effect on human body. It is necessary to consider such a drug as a mixture of two compounds (drug enantiomers), with their own effect on the human body. The present paper describes a simple and sensitive LC–MS method for the stereoselective determination of THP in human serum. In this study, the sample was prepared by a solid-phase extraction (SPE) procedure. The enantiomer separation was done using native …

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[2,3:5,6]Dibenzo[2.2.2]Octa-2,5,7-Triene (C2/C) And [2,3:5,6]Dibenzo[2.2.2]Octa-2,5-Diene, Lary Burrows, John M. Masnovi, Ronald J. Baker Feb 1999

[2,3:5,6]Dibenzo[2.2.2]Octa-2,5,7-Triene (C2/C) And [2,3:5,6]Dibenzo[2.2.2]Octa-2,5-Diene, Lary Burrows, John M. Masnovi, Ronald J. Baker

Chemistry Faculty Publications

Two barrelene homologs are reported. Strain in the bicyclic framework of [2,3:5,6]dibenzo[2.2.2]octa-2,5,7- triene, (I) (C16H12), which is manifest in the deviations from ideality of the bond angles in the central bicyclic ringoSyStem and compression of the double bond [1.312 (3)A], is reduced in the more saturated derivative, [2,3:5,6]dibenzo[2.2.2]octa-2,5-diene, (II) (CI6H14), with the corresponding single bond being 1.5380 (19)A. The formation of isomorphs of (I) in both chiral (C2) and achiral (C2/c) space groups has implications for asymmetric syntheses involving solid (I) which rely on a non-centrosymmetric space group.

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Phorbol 12-Myristate 13-Acetate Stimulates Lysophosphatidic Acid Secretion From Ovarian And Cervical Cancer Cells But Not From Breast Or Leukemia Cells, Zhongzhou Shen, Jerome Belinson, Richard E. Morton, Yan Xu Dec 1998

Phorbol 12-Myristate 13-Acetate Stimulates Lysophosphatidic Acid Secretion From Ovarian And Cervical Cancer Cells But Not From Breast Or Leukemia Cells, Zhongzhou Shen, Jerome Belinson, Richard E. Morton, Yan Xu

Chemistry Faculty Publications

Lysophosphatidic acid (LPA) is present in ascites from patients with ovarian cancer. It stimulates calcium release and growth of ovarian cancer cells bothin vitroandin vivo.Recently, we found that LPA levels were significantly elevated in plasma from patients with ovarian cancer and other gynecological cancers. In contrast, LPA levels were not elevated in patients with breast cancer and leukemias. In view of this, we investigated whether gynecological cancer cells could produce LPA. LPA was extracted from the supernatant of cells culturedin vitroand purified by thin layer chromatography. After hydrolysis and transmethylation, the fatty acid derivatives were analyzed by gas chromatography. We …

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Simultaneous Formation Of Functional Leading And Lagging Strand Holoenzyme Complexes On A Small, Defined Dna Substrate, Anthony J. Berdis, Stephen J. Benkovic Sep 1998

Simultaneous Formation Of Functional Leading And Lagging Strand Holoenzyme Complexes On A Small, Defined Dna Substrate, Anthony J. Berdis, Stephen J. Benkovic

Chemistry Faculty Publications

The biochemical characterization of leading and lagging strand DNA synthesis by bacteriophage T4 replication proteins has been addressed utilizing a small, defined primer/template. The ATP hydrolysis activity of 44/62, the clamp loading complex responsible for holoenzyme assembly, was monitored during assembly of both the leading and lagging strand holoenzyme complex. The ATPase activity of 44/62 diminishes once a functional holoenzyme is assembled on both the leading and lagging strand. The assembly of the lagging strand holoenzyme is facilitated by several factors including biotinylated streptavidin blocks at the end of the fork strands, preassembly of the leading strand holoenzyme, and by …

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Electron Transfer Catalysis Of The Hydrogenolysis Of Acyl Dicarbonyl Cyclopentadienyliron Complexes By Tributyltin Hydride, Christian Amatore, Mekki Bayachou, Olivier Buriez, Jean Noel Verpeaux Sep 1998

Electron Transfer Catalysis Of The Hydrogenolysis Of Acyl Dicarbonyl Cyclopentadienyliron Complexes By Tributyltin Hydride, Christian Amatore, Mekki Bayachou, Olivier Buriez, Jean Noel Verpeaux

Chemistry Faculty Publications

The conversion of acyl dicarbonyl cyclopentadienyliron compounds Cp(CO)2Fe(COR) into aldehydes is not straightforward. It is shown here, mainly from electrochemical results, that the hydrogenolysis of the metal acyl bond can be efficiently achieved by trialkytin hydrides under very mild conditions, according to a chain reaction process initiated by an electron transfer to the acyl complex. The expected aldehyde is formed together with the heterobinuclear iron-tin complex.

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A Cell Cycle-Regulated Adenine Dna Methyltransferase From Caulobacter Crescentus Processively Methylates Gantc Sites On Hemimethylated Dna, Anthony J. Berdis, Irene Lee, James K. Coward, Craig Stephens, Rachel Wright, Lucy Shapiro, Stephen J. Benkovic Mar 1998

A Cell Cycle-Regulated Adenine Dna Methyltransferase From Caulobacter Crescentus Processively Methylates Gantc Sites On Hemimethylated Dna, Anthony J. Berdis, Irene Lee, James K. Coward, Craig Stephens, Rachel Wright, Lucy Shapiro, Stephen J. Benkovic

Chemistry Faculty Publications

The kinetic properties of an adenine DNA methyltransferase involved in cell cycle regulation of Caulobacter crescentus have been elucidated by using defined unmethylated or hemimethylated DNA (DNAHM) substrates. Catalytic efficiency is significantly enhanced with a DNAHM substrate. Biphasic kinetic behavior during methyl incorporation is observed when unmethylated or DNAHM substrates are used, indicating that a step after chemistry limits enzyme turnover and is most likely the release of enzyme from methylated DNA product. The enzyme is thermally inactivated at 30°C within 20 min; this process is substantially decreased in the presence of saturating concentrations of DNAHM, suggesting that the enzyme …

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Assembly And Disassembly Of Dna Polymerase Holoenzyme, Daniel J. Sexton, Anthony J. Berdis, Stephen J. Benkovic Oct 1997

Assembly And Disassembly Of Dna Polymerase Holoenzyme, Daniel J. Sexton, Anthony J. Berdis, Stephen J. Benkovic

Chemistry Faculty Publications

The complex task of genomic replication requires a large collection of proteins properly assembled within the close confines of the replication fork. The mechanism and dynamics of holoenzyme assembly and disassembly have been investigated using steady state and pre-steady state methods as opposed to structural studies, primarily due to the intrinsic transient nature of these protein complexes during DNA replication. The key step in bacteriophage T4 holoenzyme assembly involves ATP hydrolysis, whereas disassembly is mediated by subunit dissociation of the clamp protein in an ATP-independent manner.

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Enhancing The Performance Of Membrane Introduction Mass Spectrometry By Organic Carrier And Liquid Chromatographic Separation, Shi Ouyang, Yong Hong Chen, Yan Xu Jan 1997

Enhancing The Performance Of Membrane Introduction Mass Spectrometry By Organic Carrier And Liquid Chromatographic Separation, Shi Ouyang, Yong Hong Chen, Yan Xu

Chemistry Faculty Publications

A method of membrane introduction mass spectrometry with liquid chromatographic separation (LC/MIMS) for the analysis of volatile organic compounds (VOCs) in water has been developed. The method not only inherited all the advantages of membrane introduction mass spectrometry by flow-injection analysis (FIA/MIMS), but also expanded the application of MIMS to the determination of compounds with identical quantitation ions. Because the quantitation by LC/MIMS is based on two-dimensional identification (retention time (tr) and mass-to-charge ratio ()), it provides a tangible approach to the analysis of VOCs in complex aqueous samples. In this work, a C18 column and a mobile phase (methanol/water) …

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Protein-Protein And Protein-Dna Interactions At The Bacteriophage T4 Dna Replication Fork. Characterization Of A Fluorescently Labeled Dna Polymerase Sliding Clamp, Daniel J. Sexton, Theodore E. Carver, Anthony J. Berdis, Stephen J. Benkovic Nov 1996

Protein-Protein And Protein-Dna Interactions At The Bacteriophage T4 Dna Replication Fork. Characterization Of A Fluorescently Labeled Dna Polymerase Sliding Clamp, Daniel J. Sexton, Theodore E. Carver, Anthony J. Berdis, Stephen J. Benkovic

Chemistry Faculty Publications

The T4 DNA polymerase holoenzyme is composed of the polymerase enzyme complexed to the sliding clamp (the 45 protein), which is loaded onto DNA by an ATP-dependent clamp loader (the 44/62 complex). This paper describes a new method to directly investigate the mechanism of holoenzyme assembly using a fluorescently labeled cysteine mutant of the 45 protein. This protein possessed unaltered function yet produced substantial changes in probe fluorescence intensity upon interacting with other components of the holoenzyme. These fluorescence changes provide insight into the role of ATP hydrolysis in holoenzyme assembly. Using either ATP or the non-hydrolyzable ATP analog, adenosine …

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The Carboxyl Terminus Of The Bacteriophage T4 Dna Polymerase Is Required For Holoenzyme Complex Formation, Anthony J. Berdis, Patrice Soumillion, Stephen J. Benkovic Nov 1996

The Carboxyl Terminus Of The Bacteriophage T4 Dna Polymerase Is Required For Holoenzyme Complex Formation, Anthony J. Berdis, Patrice Soumillion, Stephen J. Benkovic

Chemistry Faculty Publications

To further elucidate the mechanism and dynamics of bacteriophage T4 holoenzyme formation, a mutant polymerase in which the last six carboxyl-terminal amino acids are deleted, was constructed, overexpressed, and purified to homogeneity. The mutant polymerase, designated ΔC6 exo−, is identical to wild-type exo− polymerase with respect to kcat, kpol, and dissociation constants for nucleotide and DNA substrate. However, unlike wild-type exo− polymerase, the ΔC6 exo− polymerase is unable to interact with the 45 protein to form the stable holoenzyme. A synthetic polypeptide corresponding to the carboxyl terminus of the wild-type exo− polymerase was tested as an in vitro inhibitor of …

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Indirect Ultraviolet Detection Of Biologically Relevant Organic Acids By Capillary Electrophoresis, Hong Chen, Yan Xu, Frederick Van Lente, Michael P.C. Ip Apr 1996

Indirect Ultraviolet Detection Of Biologically Relevant Organic Acids By Capillary Electrophoresis, Hong Chen, Yan Xu, Frederick Van Lente, Michael P.C. Ip

Chemistry Faculty Publications

Indirect UV detection of fourteen short-chain organic acids (e.g., oxalic acid, citric acid, malonic acid, tartaric acid, methylmalonic acid, α-ketoglutaric acid, succinic acid, ethylmalonic acid, methylsuccinic acid, glutaric acid, apidic acid, methylglutaric acid, lactic acid and pyruvic acid) by capillary electrophoresis is described. The method used phthalate as the UV-absorbing additive in carbonate buffer and the non-absorbing analytes were detected indirectly at 230 nm. The influences of buffer pH, ionic strenght, concentration of phthalate and organic modifier on indirect signal response and migration behavior of the organic acids were investigated. Comparisons of reproducibility on migration time, limit of detection and …

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