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S Sun

Publications and source records attributed to S Sun.

At least 253 records · Page 14Linked to original sources
PubMed1995

Cryo-electron energy loss spectroscopy: observations on vitrified hydrated specimens and radiation damage.

Valence electron energy loss spectroscopy (EELS) has been used to characterize the composition of frozen-hydrated specimens in the electron microscope. Fine structure in the energy range up to 30 eV provides a means of distinguishing between vitreous and crystalline ice. Some features of the ice spectrum can be understood in terms of transitions between molecular orbitals in the water molecule and by the existence of excitons in the solid. Spectra from hydrated biological specimens can be analyzed to obtain quantitative estimates of the water content by fitting contributions from the ice and organic components. EELS also provides information about the radiation chemistry that occurs when hydrated specimens are exposed to the electron beam. From the observation of the hydrogen K-edge at approximately 13 eV, it can be deduced that bubbles of molecular hydrogen are evolved during irradiation at doses of > 10(4) nm-2, and that these bubbles contain gas at pressures in excess of one thousand atmospheres.

Animals↗
PubMed1995

A genetic algorithm that seeks native states of peptides and proteins.

We describe a computer algorithm to predict native structures of proteins and peptides from their primary sequences, their known native radii of gyration, and their known disulfide bonding patterns, starting from random conformations. Proteins are represented as simplified real-space main chains with single-bead side chains. Nonlocal interactions are taken from structural database-derived statistical potentials, as in an earlier treatment. Local interactions are taken from simulations of (phi, psi) energy surfaces for each amino acid generated using the Biosym Discover program. Conformational searching is done by a genetic algorithm-based method. Reasonable structures are obtained for melittin (a 26-mer), avian pancreatic polypeptide inhibitor (a 36-mer), crambin (a 46-mer), apamin (an 18-mer), tachyplesin (a 17-mer), C-peptide of ribonuclease A (a 13-mer), and four different designed helical peptides. A hydrogen bond interaction was tested and found to be generally unnecessary for helical peptides, but it helps fold some sheet regions in these structures. For the few longer chains we tested, the method appears not to converge. In those cases, it appears to recover native-like secondary structures, but gets incorrect tertiary folds.

Algorithms↗
PubMed1995

Effect of carotenoids on in vitro immunoglobulin production by human peripheral blood mononuclear cells: astaxanthin, a carotenoid without vitamin A activity, enhances in vitro immunoglobulin production in response to a T-dependent stimulant and antigen.

The effect of carotenoids on in vitro immunoglobulin (Ig) production by peripheral blood mononuclear cells (PBMNC) was examined by employing blood samples from adult volunteers and full-term newborn babies (umbilical cord blood). Under carotenoid-supplemented culture conditions, cells were stimulated by polyclonal stimulants, neoantigens, and a recall antigen (Ag), and IgM, IgA, and IgG levels in the culture supernatant were measured. Beta-carotene and astaxanthin were used as representatives of carotenoids with and without vitamin A activity, respectively. Astaxanthin enhanced IgM production in response to T-dependent Ag (TD-Ag) and a T-dependent polyclonal stimulant. Astaxanthin also augmented IgG production in response to a recall Ag. IgA production without supplemental carotenoids was negligible for all stimuli. However, in carotenoid-supplemented cultures, IgA production was significantly higher in response to a T-dependent polyclonal stimulant than in unsupplemented cultures. IgM and IgA production was augmented at 10(-8) mol/l astaxanthin, whereas astaxanthin enhanced IgG production in response to a recall Ag at 10(-10)-10(-9) mol/l. Similar enhancing actions of astaxanthin on IgM production were observed in cord blood mononuclear cells (CBMNC), although CBMNC produced less IgM than adult PBMNC. Beta-carotene did not have a significant effect on human Ig production. The carotenoid actions were not demonstrated under serum-free culture conditions; serum is essential for solubilization of carotenoids. In summary, this study has shown for the first time that astaxanthin, a carotenoid without vitamin A activity, enhances human Ig production in response to T-dependent stimuli.

Adult↗
PubMed1995

Astaxanthin, a carotenoid without vitamin A activity, augments antibody responses in cultures including T-helper cell clones and suboptimal doses of antigen.

Astaxanthin, a carotenoid without vitamin A activity, enhances T-dependent antigen (Ag)-specific humoral immune responses. We examined carotenoid actions on T-helper (Th) cell activity in a direct manner with reconstitution experiments; spleen Th cells were replaced with Ag-specific Type 1 and Type 2 (Th1 and Th2) Th cell clones. The Ag for the Th1 and Th2 clones were pigeon cytochrome C and rabbit gamma-globulin, respectively. Astaxanthin and beta-carotene augmented the number of IgM antibody (Ab)-secreting cells when unprimed B cells were incubated with Th clones and stimulated with suboptimal doses of Ag specific for each Th clone. The number of IgG Ab-secreting cells were greater with use of in vivo primed B cells than with unprimed B cells in both Th clones. Astaxanthin but not beta-carotene augmented the number of IgG Ab-secreting cells when primed B cells and Th cell clones were stimulated with suboptimal doses of Ag specific for each Th clone. In the presence of optimal doses of Ag for each Th clone, neither carotenoid augmented the number of Ab-secreting cells. Astaxanthin and beta-carotene may enhance the actions of both Th1 and Th2 cells for humoral immune responses with suboptimal Ag challenges; certain carotenoids may help maintain Ag-mediated immune responses at optimal levels.

Animals↗
PubMed1995

Polynucleotides compensate for impaired T-dependent antibody production induced in C57B1/6 mice by a nucleotide-free diet both in vivo and in vitro, but a mononucleotide-nucleoside mixture is effective only in vivo.

Actions of nucleotides on in vitro humoral immune responses were studied in mice fed a nucleotide-free diet, a nucleotide-free diet plus a mononucleotide-nucleoside mixture or a nucleotide-free diet plus yeast RNA (polynucleotides). Cultured spleen cells from mice fed a nucleotide-free diet produced fewer numbers of antibody-secreting cells in response to a T-dependent antigen, compared with those from controls fed nucleotide-supplemented diets. Immunoglobulin M concentrations in these supernatants were significantly lower in cultured cells from mice fed the nucleotide-free diet or the nucleotide-free diet plus the mononucleotide/nucleoside mixture compared with concentrations in cells from mice fed the nucleotide-free diet plus RNA. Concanavalin A-potentiated cytokine (interleukin-4 and interleukin-5) production by purified T helper cells was also lower in cultured cells from mice fed a nucleotide-free diet than in those from mice fed nucleotide-supplemented diets. In vivo supplementation with the mononucleotide/nucleoside mixture restored impaired in vitro antibody and concanavalin A-potentiated cytokine production in mice fed a nucleotide-free diet. However, addition of RNA to the culture enhanced antibody production in spleen cells from mice of all diet groups. Supplementing the culture with RNA did not enhance mitogen-potentiated cytokine production. This in vitro action of RNA was retained after the removal of oligonucleotides (molecular weight < 1000), but was reduced by modification of bases and cleavage of phosphodiester bonds of RNA. Thus the in vitro action of RNA is mainly attributed to polynucleotides, indicating their potential role in modulation of local humoral immune responses in the body.

Animals↗
PubMed1995

Designing amino acid sequences to fold with good hydrophobic cores.

We present two methods for designing amino acid sequences of proteins that will fold to have good hydrophobic cores. Given the coordinates of the desired target protein or polymer structure, the methods generate sequences of hydrophobic (H) and polar (P) monomers that are intended to fold to these structures. One method designs hydrophobic inside, polar outside; the other minimizes an energy function in a sequence evolution process. The sequences generated by these methods agree at the level of 60-80% of the sequence positions in 20 proteins in the Protein Data Bank. A major challenge in protein design is to create sequences that can fold uniquely, i.e. to a single conformation rather than to many. While an earlier lattice-based sequence evolution method was shown not to design unique folders, our method generates unique folders in lattice model tests. These methods may also be useful in designing other types of foldable polymer not based on amino acids.

Amino Acid Sequence↗
PubMed1995

A simple protein folding algorithm using a binary code and secondary structure constraints.

We describe an algorithm to predict tertiary structures of small proteins. In contrast to most current folding algorithms, it uses very few energy parameters. Given the secondary structural elements in the sequence--alpha-helices and beta-strands--the algorithm searches the remaining conformational space of a simplified real-space representation of chains to find a minimum energy of an exceedingly simple potential function. The potential is based only on a single type of favorable interaction between hydrophobic residues, an unfavorable excluded volume term of spatial overlaps and, for sheet proteins, an interstrand hydrogen bond interaction. Where appropriate, the known disulfide bonds are constrained by a square-law potential. Conformations are searched by a genetic algorithm. The model predicts reasonably well the known tertiary folds of seven out of the 10 small proteins we consider. We draw two conclusions. First, for the proteins we tested, this exceedingly simple potential function is no worse than others having hundreds of energy parameters in finding the right general tertiary structures. Second, despite its simplicity, the potential function is not the weak link in this algorithm. Differences between our predicted structures and the correct targets can be ascribed to shortcomings in our search strategy. This potential function may be useful for testing other conformational search strategies.

Algorithms↗
PubMed1995

Effect of arrest time on the hemodynamic efficacy of precordial compression.

OBJECTIVES: To evaluate the efficacy of conventional threshold levels of coronary perfusion pressure and end-tidal CO2 as predictors of resuscitability after prolonged cardiac arrest. DESIGN: Prospective, randomized, controlled animal study. SETTING: University research laboratory. SUBJECTS: Twenty-one Sprague-Dawley rats, including three groups of seven animals in each group. INTERVENTIONS: Ventricular fibrillation was untreated for 9, 12, or 15 mins. After an additional 5-min interval of precordial compression, external direct current defibrillation was attempted. MEASUREMENTS AND MAIN RESULTS: All animals were successfully resuscitated after 9 mins of ventricular fibrillation but less than one half of the animals were successfully resuscitated after 15 mins of ventricular fibrillation. Each of seven animals survived for 24 hrs after 9 mins of untreated ventricular fibrillation but none of the animals survived after 15 mins of ventricular fibrillation. In this experimental setting, neither coronary perfusion pressure nor end-tidal CO2 produced by precordial compression was predictive of outcomes when the animals underwent progressively longer intervals of untreated cardiac arrest. CONCLUSIONS: The efficacy of precordial compression--as measured by coronary perfusion pressure and end-tidal CO2 concentration after prolongation of untreated cardiac arrest--was not overtly compromised. However, the previously established critical threshold levels of coronary perfusion pressure and end-tidal CO2 failed as predictors of resuscitability after prolonged intervals of untreated cardiac arrest.

Animals↗
PubMed1995

Negative regulation of the vascular smooth muscle alpha-actin gene in fibroblasts and myoblasts: disruption of enhancer function by sequence-specific single-stranded-DNA-binding proteins.

Transcriptional activation and repression of the vascular smooth muscle (VSM) alpha-actin gene in myoblasts and fibroblasts is mediated, in part, by positive and negative elements contained within an approximately 30-bp polypurine-polypyrimidine tract. This region contains binding sites for an essential transcription-activating protein, identified as transcriptional enhancer factor I (TEF-1), and two tissue-restrictive, sequence-specific, single-stranded-DNA-binding activities termed VACssBF1 and VACssBF2. TEF-1 has no detectable single-stranded-DNA-binding activity, while VACssBF1 and VACssBF2 have little, if any, affinity for double-stranded DNA. Site-specific mutagenesis experiments demonstrate that the determinants of VACssBF1 and VACssBF2 binding lie on opposite strands of the DNA helix and include the TEF-1 recognition sequence. Functional analysis of this region reveals that the CCAAT box-binding protein nuclear factor Y (NF-Y) can substitute for TEF-1 in activating VSM alpha-actin transcription but that the TEF-1-binding site is essential for the maintenance of full transcriptional repression. Importantly, replacement of the TEF-1-binding site with that for NF-Y diminishes the ability of VACssBF1 and VACssBF2 to bind to separated single strands. Additional activating mutations have been identified which lie outside of the TEF-1-binding site but which also impair single-stranded-DNA-binding activity. These data support a model in which VACssBF1 and VACssBF2 function as repressors of VSM alpha-actin transcription by stabilizing a local single-stranded-DNA conformation, thus precluding double-stranded-DNA binding by the essential transcriptional activator TEF-1.

Actins↗
PubMed1995

Airway protection during experimental CPR.

BACKGROUND: Experimental studies recently demonstrated that positive pressure ventilation may not be essential for initial cardiopulmonary resuscitation. Nevertheless, oxygen enrichment of inspired gas mixtures and spontaneous gasping were associated with increased resuscitability and survival after cardiac arrest. However, as yet unresolved is the benefit of early airway control under conditions simulating "sudden death" due to ventricular fibrillation. METHODS: Twenty adult, male Sprague-Dawley rats were randomly assigned to one of two groups in which the airway was unprotected or protected by an oropharyngeal airway of our design. Cardiac arrest was induced by an alternating current delivered to the right ventricular endocardium. Oxygen was delivered to a hood that was loosely applied over the head of the each animal at a flow rate of 1 L/min. Precordial compression was initiated after 4 min of untreated ventricular fibrillation and defibrillation was attempted 6 min later. After spontaneous circulation had been restored, a tracheostomy was performed and the animals were mechanically ventilated with 100% oxygen for an additional interval of 1 h. Animals were then returned to their cages and observed for an additional 24 h. RESULTS: Spontaneous circulation was restored in each of the animals who had an oropharyngeal airway and nine of ten animals in the absence of an artificial airway. In each group, seven animals survived for more than 24 h. Animals in which the airway had been protected had significantly greater frequency of spontaneous gasping (28 +/- 13/min vs 13 +/- 9/min; p < 0.05) and significantly higher arterial oxygen saturation (77 +/- 19% vs vs 55 +/- 25%; p < 0.05). CONCLUSION: In the setting of experimental cardiac resuscitation, the insertion of an artificial airway increased the frequency of spontaneous gasping and arterial oxygenation. Nevertheless, no significant differences in resuscitability or postresuscitation survival were associated with insertion of the artificial airway.

Airway Obstruction↗
PubMed1995

Tumor necrosis factor-induced necrosis: a monocyte-mediated hypercoagulable effect.

The mechanisms by which tumor necrosis factor (TNF) exerts its necrotic effects are somewhat obscure. We hypothesize that TNF, by monocyte activation, produces the procoagulant tissue factor, thus leading to a state of hypercoagulability with resultant thrombotic vascular occlusion and tissue necrosis. To test this hypothesis, modified recalcification time values (in minutes +/- standard deviation) were obtained on aliquots of blood with A) 20 microL of albumin, B) 20 microL of saline containing endotoxin, and C) 20 microL of albumin with 450 units of TNF. No differences were noted if the samples were not incubated. We conclude that TNF, can cause tumor (tissue) necrosis, and since incubation is required, TNF alone (without monocyte activation) has no procoagulant activity.

Blood Coagulation↗
PubMed1995

Lessons learned from autopsies at a pediatric teaching hospital.

Twenty-six percent of pediatric patients had discrepant major diagnoses revealed at autopsy. A printed form used to document permission for autopsies improved the autopsy rate. No variables were found to predict the success rate for obtaining autopsies.

Autopsy↗
PubMed1995

[Assessment of effectiveness of AgSD-ZnSD-Azone cream, negative ion irradiation and "moisture burn ointment" in prevention of burn wound infection as judged by changes in LPS, TNF and ET levels].

40 Wistar rats were scalded resulting in 15% TBSA full-thickness burn. Pseudomonas aeruginosa (10(9)/ml) was seeded on the wounds. The animals were divided into 4 groups. AgSD and ZnSD (with Azone) cream was applied to the wounds in the group I. The wounds were irradiated with negative ion current in the group II. The "moisture burn ointment" was applied to the wounds in the group III. Group IV consisted of controls without any treatment. Judging by changes in levels of LPS, TNF and ET, it was shown that the best result was obtained in the group I and II. The "moisture burn ointment" group yielded the poorest results.

Animals↗
PubMed1995

[Analysis of the results of fibrobronchoscopy relevant to x-ray examination in 138 cases with hemoptysis].

Only 90 abnormal cases of the chest X-ray examination were found among 138 patients with hemoptysis. However the main results of the fibrobronchoscopy for 138 cases were: chronic bronchitis and pulmonary inflammation 59 cases (42.8%), bronchogenic carcinoma 41 cases (29.7%), tuberculosis 10 cases (7.2%) and others 28 cases (20.3%). Authors conclude that fibrobronchoscopy can clarify the nature of lesions and the cause of hemoptysis on the basis of chest X-ray examination.

Adenocarcinoma↗
PubMed1995

[Production and application of mouse antiserum to human estrogen receptors].

An antiserum to peptide containing 15 amino acids corresponding to the region-D of human estrogen receptors (hERD) was obtained in mice by immunization with the peptide conjngated to KLH. Using this antiserum, the ER status of paraffin-embeded sections of 95 human breast carcinomas (in which, sections of 31 were both frozen and paraffin-embeded ones) were studied. The corresponding rate for determination of ER status between immunohistochemical staining (IHC) and dextran coated charcoal (DCC) assay was 89.5%. The concordance rate for semiquantitative gradings was 69.3%. In addition, in situ hybridization (ISH) of 15 frozen sections of the samples using digoxigenin labeled dUTP to identify the expression of ER mRNA was also done. The result of ISH was fully consistent with that of IHC (100%). The results show that the mouse antiserum to hERD obtained in this study is specific and sensitive for IHC assay of ER and IHC is a valuable adjunct and/or alternative to the biochemical method for determination of the ER status of breast cancer.

Animals↗