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C Li

Publications and source records attributed to C Li.

At least 1,063 records · Page 59Linked to original sources
PubMed1993

5-lipoxygenase-activating protein stimulates the utilization of arachidonic acid by 5-lipoxygenase.

5-Lipoxygenase (5-LO) and its activating protein (FLAP) are both required for cellular leukotriene (LT) synthesis, with 5-LO catalyzing both the synthesis of (5S)-5-hydroperoxy-6,8,11,14-eicosatetraenoic acid (5-HPETE) from arachidonic acid and the subsequent synthesis of LTA4 from 5-HPETE. We have previously expressed both human 5-LO and human FLAP to high levels in Spodoptera frugiperda (Sf9) insect cells, using recombinant baculoviruses. To study the mechanism by which FLAP activates 5-LO, we compared cellular 5-LO activity in Sf9 cells expressing this enzyme to that in Sf9 cells coexpressing FLAP and 5-LO. In this system, FLAP stimulates the utilization of arachidonic acid by 5-LO as a substrate, and increases the efficiency with which 5-LO converts 5-HPETE to LTA4. LT synthesis in cells coexpressing FLAP and 5-LO is inhibited by 3-[1-(p-chlorophenyl)-5-isopropyl-3-tert-butylthio-1H-indol-2-yl]-2,2- dimethyl-propanoic acid (MK-886), an LT biosynthesis inhibitor which specifically binds to FLAP. These studies in Sf9 cells, together with our recent demonstration that FLAP specifically binds arachidonic acid, suggests that FLAP activates 5-LO by acting as an arachidonic acid transfer protein.

5-Lipoxygenase-Activating Proteins↗
PubMed1993

Circular dichroism studies of diethyl pyrocarbonate-modified histidine in hen egg white lysozyme.

The single histidine residue (His-15) in hen egg white lysozyme (EC 3.2.1.17) was chemically modified by diethyl pyrocarbonate (DEPC) to form exclusively the mono-N-carbethoxyimidazole adduct (second order rate constant of 252 +/- 16 M-1 min-1). Irreversible biscarbethoxylation of the His-15 imidazole ring by DEPC was observed when lysozyme was pretreated with 2-mercaptoethanol (2-ME), 2-ME plus 8 M urea, or 2-ME plus 1% (w/v) sodium dodecyl sulfate (SDS). Circular dichroism difference spectra were measured for the mono-N-carbethoxyimidazole derivatives of lysozyme, N alpha-acetyl-L-histidine, angiotensin-II, and O-carbethoxy-N alpha-acetyl-L-tyrosine. The circular dichroism difference spectrum for mono-N-carbethoxy lysozyme had one main band (delta [theta]244 nm = +17,000 degree. cm2.dmol-1) in the 240-260 nm region. Denaturing mono-N-carbethoxy lysozyme with 2-ME and 8 M urea (55 degrees C) or 1% SDS (100 degrees C) essentially abolished its circular dichroism difference spectrum in the 240-260 nm region without any decarbethoxylation. In this same region the circular dichroism difference spectra of DEPC-modified N alpha-acetyl-L-histidine and DEPC-modified angiotensin-II had two much weaker bands (delta [theta]233 nm = +1000 degree.cm2.dmol-1 and delta[theta]252nm = -600 degree.cm2.dmol-1 for N alpha-acetyl-L-histidine). This study reports the first characterization of circular dichroism associated with mono-N-carbethoxyhistidine in an enzyme (lysozyme), a peptide (angiotensin-II), and a model compound (N alpha-acetyl-L-histidine).

Amino Acid Sequence↗
PubMed1993

Exoquence DNA sequencing.

We have developed a strategy for DNA sequencing based on exonuclease III digestion followed by double strand specific endonuclease digestion and direct dideoxynucleotide sequencing reaction. This strategy eliminates the need for subcloning, oligonucleotide primers, and prior knowledge of the DNA to be sequenced. All template and primer duplexes needed for sequencing a complete insert can be prepared in one day from uncharacterized starting DNA. Sequence information can be obtained from different regions of the DNA simultaneously. The method uses double-stranded DNA to generate single-stranded template and primer, and thus produces high quality sequence results. Commercially available dideoxy-sequencing kits are well suited for this method. The strategy should be applicable for both automatic and routine laboratory DNA sequencing.

Exodeoxyribonucleases↗
PubMed1993

Multiple pathways for protein transport into or across the thylakoid membrane.

Many thylakoid proteins are cytosolically synthesized and have to cross the two chloroplast envelope membranes as well as the thylakoid membrane en route to their functional locations. In order to investigate the localization pathways of these proteins, we over-expressed precursor proteins in Escherichia coli and used them in competition studies. Competition was conducted for import into the chloroplast and for transport into or across isolated thylakoids. We also developed a novel in organello method whereby competition for thylakoid transport occurred within intact chloroplasts. Import of all precursors into chloroplasts was similarly inhibited by saturating concentrations of the precursor to the OE23 protein. In contrast, competition for thylakoid transport revealed three distinct precursor specificity groups. Lumen-resident proteins OE23 and OE17 constitute one group, lumenal proteins plastocyanin and OE33 a second, and the membrane protein LHCP a third. The specificity determined by competition correlates with previously determined protein-specific energy requirements for thylakoid transport. Taken together, these results suggest that thylakoid precursor proteins are imported into chloroplasts on a common import apparatus, whereupon they enter one of several precursor-specific thylakoid transport pathways.

Base Sequence↗
PubMed1993

Further purification and characterization of a multienzyme complex for DNA synthesis in human cells.

The 21 S complex of enzymes for DNA synthesis in the combined low salt nuclear extract-post microsomal supernatant from HeLa cells [Malkas et al. (1990) Biochemistry 29:6362-6374] was purified by poly (ethylene glycol) precipitation, Q-Sepharose chromatography, Mono Q Fast Protein Liquid Chromatography (FPLC), and velocity gradient centrifugation. The procedure gives purified enzyme complex at a yield of 45%. The 21 S enzyme complex remains intact and functional in the replication of simian virus 40 DNA throughout the purification. Sedimentation analysis showed that the 21 S enzyme complex exists in the crude HeLa cell extract and that simian virus 40 in vitro DNA replication activity in the cell extract resides exclusively with the 21 S complex. The results of enzyme and immunological analysis indicate that DNA polymerase alpha-primase, a 3',5' exonuclease, DNA ligase I, RNase H, and topoisomerase I are associated with the purified enzyme complex. Denaturing polyacrylamide gel electrophoresis of the purified enzyme complex showed the presence of about 30 polypeptides in the size range of 300 to 15 kDa. Immunofluorescent imaging analysis, with antibodies to DNA polymerase alpha,beta and DNA ligase I, showed that polymerase alpha and DNA ligase I are localized to granular-like foci within the nucleus during S-phase. In contrast, DNA polymerase beta, which is not associated with the 21 S complex, is diffusely distributed throughout the nucleoplasm.

Base Sequence↗
PubMed1993

Cellular and chemical mediators of type 1 hypersensitivity in calves infected with Ostertagia ostertagi: histamine, prostaglandin D2, prostaglandin E2 and leukotriene C4.

Plasma histamine, prostaglandin E2 (PG) D2, PGE2, and leukotriene (LT) C4 levels were determined in 26 Holstein steers before and after natural or experimental infection with Ostertagia ostertagi. Post-infection abomasal lymph was also assayed for PGD2, PGE2, and LTC4. Histamine determinations were performed on abomasal tissue from three locations. Results showed that: (1) tissue histamine levels increased in steers with type 2 ostertagiosis, (2) lymphatic PGD2 and PGE2 levels were increased, probably as a result of macrophage activity, (3) lymphatic LTC4 levels increased in steers with type 1 ostertagiosis, and were correlated with tissue eosinophilia, and (4) plasma levels of PGD2, PGE2, LTC4 and histamine were not useful for predicting worm burdens. These findings suggest a functional role for eosinophils and mast cells in the pathophysiology of ostertagiosis, through mediation of a type 1 hypersensitivity reaction.

Animals↗
PubMed1993

Carbethoxylation of coordinated histidine by diethylpyrocarbonate.

The metastable, reversible carbethoxylation of histidine in the cobalt(III) complexes (ethylene-diamine)(histidine)chlorocobalt(III) chloride, [Co(III)(en)ClHis]Cl, and (diethylenetriamine) (histidine)cobalt(III) dichloride, [Co(III)(dien)His]Cl2, following reaction with diethylpyrocarbonate, was observed using UV spectroscopy. These observations indicate that diethylpyrocarbonate can react with a coordinated imidazole ring. CD transitions associated with coordinated carbethoxyhistidine in [Co(III)(en)ClHis]Cl and [Co(III)(dien)His]Cl2 were also observed. The molar ellipticities of the CD bands observed for carbethoxy [Co(III)(en)ClHis]Cl or carbethoxy [Co(III) (dien)His]Cl2 are much larger than the molar ellipticities of the CD transition associated with carbethoxy N alpha-acetyl-L-histidine, indicating that loss of rotational freedom of the imidazole ring could be a major factor in the enhanced CD.

Circular Dichroism↗
PubMed1993

Central behavioral interactions between ethanol, (-)-nicotine, and (-)-cotinine in mice.

A high correlation between alcohol use and smoking has long been suggested by epidemiological data. We examined the potential behavioral interactions between ethanol and nicotine using ethanol-induced motor incoordination as the test response in mice. Effect of pretreatment of various doses of (-)-nicotine, (-)-cotinine, a major metabolite of nicotine, and (+)-nicotine administered ICV on ethanol (IP)-induced motor incoordination was investigated. (-)-Nicotine (0.19, 0.38, 0.77 and, 1.54 nmoles ICV) produced significant attenuation of motor incoordination due to ethanol (2 g/kg IP) in a nearly dose-related manner which was blocked by ICV hexamethonium and trimethaphan, both purported nicotinic antagonists. (-)-Cotinine (0.35, 0.70, 1.41 nmole ICV) produced similar attenuation but was les potent than (-)-nicotine. Attenuation by (+)-nicotine (0.19, 0.38, and 0.77 nmoles ICV) was also significant but only at 0.77 nmole dose level. (+)-Nicotine-induced attenuation of motor incoordination by ethanol was antagonized by nicotinic antagonists. Data obtained suggest a central behavioral interaction between ethanol and nicotine at least through the participation of cholinergic nicotinic receptors.

Alcoholic Intoxication↗
PubMed1993

Photon beam compensation design: dose optimization in 3D volume for parallel opposed beams.

Most existing methods for photon beam compensation design is based on the dose optimization in a 2D plane through the treatment volume for each individual beam. These approaches do not, however, optimize the dose uniformity in the dimension along the beam path (hence not in the 3D volume). In this work, the author presents a practical compensation design algorithm for 3D dose optimization. In contrast to existing methods, the present algorithm simultaneously calculates the desired cross-beam transmission factor map of the compensation device for each pair of parallel opposed beams. By using computed tomography scans, the patient's external shape and the internal inhomogeneous tissue density are also taken into account. The result is used to construct beam-attenuating compensators or to program a dynamic beam delivery scheme. The algorithm is presented in a form easily adaptable to different dose calculation systems. Compared to other methods, superior dose uniformity is achieved via the present approach.

Humans↗
PubMed1993

An analysis of image segmentation time in beam's-eye-view treatment planning.

In this work we tabulate and histogram the image segmentation time for beam's eye view (BEV) treatment planning in our center. The average time needed to generate contours on CT images delineating normal structures and treatment target volumes is calculated using a data base containing over 500 patients' BEV plans. The average number of contours and total image segmentation time needed for BEV plans in three common treatment sites, namely, head/neck, lung/chest, and prostate, were estimated.

Computer Peripherals↗
PubMed1993

Computer-aided treatment design of a distal upper extremity soft tissue tumor with electron beam radiotherapy.

We present here a novel approach for the planning and treatment of a distal upper extremity soft tissue tumor. Utilizing computed tomography (CT) based electron dose calculations, a customized compensating wax bolus was designed in order to deliver sufficient dose coverage to the tumor volume while sparing the draining lymphatics of the patient's hand and digits. A clinical case is presented as well as the design and construction of the compensator. Outcome and clinical implications are discussed.

Adult↗
PubMed1993

The cystic fibrosis mutation (delta F508) does not influence the chloride channel activity of CFTR.

The cystic fibrosis transmembrane conductance regulator (CFTR) is a phosphorylation-regulated Cl- channel. In most mammalian cells, the functional consequences of the most common CF mutation, delta F508-CFTR, cannot be assessed as the mutant protein undergoes biosynthetic arrest. However, function can be studied in the baculovirus-insect cell expression system where delta F508-CFTR does not appear to undergo such arrest. Our results show that phosphorylation-regulated Cl- channel activity of delta F508-CFTR is similar to that of wild-type CFTR. This observation was confirmed in comparative studies of purified delta F508-CFTR and CFTR reconstituted in planar lipid bilayers. Therefore, we suggest that this common mutation does not result in a significant alteration in CFTR function.

Amino Acid Sequence↗
PubMed1993

Organophosphate sensitizes the human pancreas to acinar cell injury: an ultrastructural study.

Viable pancreas fragments from five human donors were incubated in oxygenated buffered Eagle Medium. The preparation and incubation conditions were based on the method of Scheele and Palade. In Group 1 there was 1-h preincubation with echothiophate (10(-4) M); then, acetylcholine (10(-5) M) was added. After 2 h tissues were prepared for electron microscopy. Acinar injury with vacuole formation was apparent. Many of these changes were observed in fragments incubated only with acetylcholine (10(-5) M) (Group 2) and in incubates with echothiophate only (10(-4) M) (Group 3); only minor changes were seen in controls with Eagle's Medium (Group 4). Large vacuoles were significantly more numerous in Group 1 than in Control Group 4 (p < 0.05). Zymogen granules were depleted in Groups 1, 2, and 3. This depletion was significant in Group 1 when compared with Group 4 (p < 0.02). These results extend previous in vitro results that showed increased amylase release after echothiophate treatment in human pancreas and a left shift in response to acetylcholine.

Acetylcholine↗
PubMed1993

Efficacy of pacemaker tachycardia termination algorithms: is electrophysiological testing alone adequate?

UNLABELLED: Selection of an optimal pacemaker tachycardia reversion algorithm is generally performed utilizing programmed electrical stimulation (PES). Multiple tachycardias are induced and various tachycardia termination protocols are tested for reversion success. However, PES may induce nonclinical tachycardia and result in an inaccurate assessment of subsequent reversion effectiveness for spontaneous tachycardia. To investigate this question, we compared tachycardia reversion protocol success for PES-induced tachycardia versus spontaneously occurring tachycardia in 16 patients with atrially placed Intermedics 262-12 antitachycardia pacemakers. The pacemaker has tachycardia response counters, and the reversion success was calculated from these counters. This was performed by comparing the percent of time 1 degree versus 2 degrees modality use occurred; crossover to the 2 degrees modality implied failure of the 1 degree modality to convert the tachycardia. PES was used to induce multiple episodes of tachycardia and spontaneous episodes of tachycardia were recorded over time by pacemaker counters. The pacemaker 1 degree modality success was then compared for spontaneous and induced arrhythmias. RESULTS: A total of 53 discrete data comparisons of PES versus spontaneous tachycardia counters were performed in the 16 patients. PES reversion success occurred 85% +/- 22% of the time versus a spontaneous reversion success of 88% +/- 22%. However, the Spearman rank correlation coefficient test demonstrated nonsignficant overall correlation (P < 0.01), and Pearson correlation on an individual patient basis varied widely (r value from < 0.1 to 1.0). CONCLUSIONS: When utilizing the same termination algorithm, the percentage conversion of tachycardias occurring spontaneously and induced by PES is similar but does not correlate well overall. This suggests that PES may not be a good linear predictor of the long-term success of antitachycardia pacing algorithms.

Adolescent↗
PubMed1993

Comparison of fluconazole and amphotericin B for treatment of experimental Candida endocarditis caused by non-C. albicans strains.

Amphotericin B and fluconazole were compared for the treatment of experimental Candida endocarditis caused by Candida tropicalis and C. parapsilosis. Rabbits received no therapy, amphotericin B (1 mg/kg of body weight per day intravenously), or fluconazole (100 mg/kg/day intraperitoneally) for either 11 or 21 days. Against both species, amphotericin B and fluconazole were equally effective overall; however, amphotericin B was more rapidly fungicidal than fluconazole in vivo against C. tropicalis.

Amphotericin B↗
PubMed1993

Adverse conditions which cause lack of flagella in Escherichia coli.

Wild-type Escherichia coli was not motile when grown in tryptone broth under the following adverse conditions: the presence of high temperature [J. Adler and B. Templeton, J. Gen. Microbiol. 46:175-184, 1967; R. B. Morrison and J. McCapra, Nature (London) 192:774-776, 1961; K. Ogiuti, Jpn. J. Exp. Med. 14:19-28, 1936], high concentrations of salts, high concentrations of carbohydrates, high concentrations of low-molecular-weight alcohols, or the pressure of gyrase inhibitors. Under all these conditions, growth was necessary for the loss of motility. This loss of motility was correlated with a reduction in the amount of cellular flagellin. We isolated and studied mutants that are resistant to suppression of motility by some of these conditions, because of the ability to synthesize flagella under these conditions. The mutations were mapped to 42 min, a region of the chromosome where many of the flagellar genes map. We also studied the effect of a preexisting gyrA mutation which allowed flagellar formation in the presence of nalidixate.

Cell Movement↗