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Biomedical subjects

S Hong

Publications and source records attributed to S Hong.

At least 73 records · Page 4Linked to original sources
PubMed2001

[A survey of pollens in Chongqing].

OBJECTIVE: In order to investigate the variety of the airborne pollen in Chongqing. METHOD: The diffusions pattern of airborne pollens in two areas of Chongqing was investigated for one year from October 1999 to September 2000. The slides were exposed daily through one year. RESULT: The peak of spreading was in March in spring and in Autumn from September to October. The test on the pollen patients shows that the main resulting pollen is in Autumn. CONCLUSION: The airborne pollen peak in Chongqing in spring prone to the influence of temperature, wind power and rain amount.

Allergens↗
PubMed2000

RbcS suppressor mutations improve the thermal stability and CO2/O2 specificity of rbcL- mutant ribulose-1,5-bisphosphate carboxylase/oxygenase.

In the green alga Chlamydomonas reinhardtii, a Leu(290)-to-Phe (L290F) substitution in the large subunit of ribulose-1, 5-bisphosphate carboxylase/oxygenase (Rubisco), which is coded by the chloroplast rbcL gene, was previously found to be suppressed by second-site Ala(222)-to-Thr and Val(262)-to-Leu substitutions. These substitutions complement the photosynthesis deficiency of the L290F mutant by restoring the decreased thermal stability, catalytic efficiency, and CO(2)/O(2) specificity of the mutant enzyme back to wild-type values. Because residues 222, 262, and 290 interact with the loop between beta strands A and B of the Rubisco small subunit, which is coded by RbcS1 and RbcS2 nuclear genes, it seemed possible that substitutions in this loop might also suppress L290F. A mutation in a nuclear gene, Rbc-1, was previously found to suppress the biochemical defects of the L290F enzyme at a posttranslational step, but the nature of this gene and its product remains unknown. In the present study, three nuclear-gene suppressors were found to be linked to each other but not to the Rbc-1 locus. DNA sequencing revealed that the RbcS2 genes of these suppressor strains have mutations that cause either Asn(54)-to-Ser or Ala(57)-to-Val substitutions in the small-subunit betaA/betaB loop. When present in otherwise wild-type cells, with or without the resident RbcS1 gene, the mutant small subunits improve the thermal stability of wild-type Rubisco. These results indicate that the betaA/betaB loop, which is unique to eukaryotic Rubisco, contributes to holoenzyme thermal stability, catalytic efficiency, and CO(2)/O(2) specificity. The small subunit may be a fruitful target for engineering improved Rubisco.

Amino Acid Sequence↗
PubMed2000

Enhancement of paclitaxel production by temperature shift in suspension culture of Taxus chinensis.

Effect of temperature shift during culture period on cell growth and paclitaxel was investigated to optimize paclitaxel production in suspension culture of Taxus chinensis. Cell growth showed the optimum at 24 degrees C while paclitaxel synthesis showed the maximum at 29 degrees C. To minimize the inhibitory effect of higher temperature on cell growth, temperature was shifted after a certain period of culture time at 24 degrees C. Paclitaxel synthesis in plant cell culture increased dramatically during day 14 to day 21 regardless of treatment, reaching the maximum production of 137.5 mg paclitaxel/L. When the temperature was maintained at 29 degrees C after day 21, the specific productivity of paclitaxel was sustained for prolonged period of 42 days. The possible relationship between temperature and paclitaxel synthetic pathway was also suggested.

Journal Article↗
PubMed2000

Apicidin, a histone deacetylase inhibitor, inhibits proliferation of tumor cells via induction of p21WAF1/Cip1 and gelsolin.

Apicidin [cyclo(N-O-methyl-L-tryptophanyl-L-isoleucinyl-D-pipecolinyl -L-2-amino-8-oxodecanoyl)] is a fungal metabolite shown to exhibit antiparasitic activity by the inhibition of histone deacetylase (HDAC). In this study, we evaluated apicidin as a potential antiproliferative agent. Apicidin showed a broad spectrum of antiproliferative activity against various cancer cell lines, although with differential sensitivity. The antiproliferative activity of apicidin on HeLa cells was accompanied by morphological changes, cell cycle arrest at G1 phase, and accumulation of hyperacetylated histone H4 in vivo as well as inhibition of partially purified HDAC in vitro. In addition, apicidin induced selective changes in the expression of p21WAF1/Cip1 and gelsolin, which control the cell cycle and cell morphology, respectively. Consistent with increased induction of p21WAF1/Cip1, phosphorylation of Rb protein was markedly decreased, indicating the inhibition of cyclin-dependent kinases, which became bound to p21WAF1/Cip1. The effects of apicidin on cell morphology, expression of gelsolin, and HDAC1 activity in vivo and in vitro appeared to be irreversible, because withdrawal of apicidin did not reverse those effects, whereas the induction of p21WAF1/Cip1 by apicidin was reversible. Taken together, the results suggest that induction of histone hyperacetylation by apicidin is responsible for the antiproliferative activity through selective induction of genes that play important roles in the cell cycle and cell morphology.

3T3 Cells↗
PubMed2000

Mitochondrial F(0)F(1) ATP synthase. Subunit regions on the F1 motor shielded by F(0), Functional significance, and evidence for an involvement of the unique F(0) subunit F(6).

Studies reported here were undertaken to gain greater molecular insight into the complex structure of mitochondrial ATP synthase (F(0)F(1)) and its relationship to the enzyme's function and motor-related properties. Significantly, these studies, which employed N-terminal sequence, mass spectral, proteolytic, immunological, and functional analyses, led to the following novel findings. First, at the top of F(1) within F(0)F(1), all six N-terminal regions derived from alpha + beta subunits are shielded, indicating that one or more F(0) subunits forms a "cap." Second, at the bottom of F(1) within F(0)F(1), the N-terminal region of the single delta subunit and the C-terminal regions of all three alpha subunits are shielded also by F(0). Third, and in contrast, part of the gamma subunit located at the bottom of F(1) is already shielded in F(1), indicating that there is a preferential propensity for interaction with other F(1) subunits, most likely delta and epsilon. Fourth, and consistent with the first two conclusions above that specific regions at the top and bottom of F(1) are shielded by F(0), further proteolytic shaving of alpha and beta subunits at these locations eliminates the capacity of F(1) to couple a proton gradient to ATP synthesis. Finally, evidence was obtained that the F(0) subunit called "F(6)," unique to animal ATP synthases, is involved in shielding F(1). The significance of the studies reported here, in relation to current views about ATP synthase structure and function in animal mitochondria, is discussed.

Adenosine Triphosphate↗
PubMed2000

CD8+ T cells rapidly acquire NK1.1 and NK cell-associated molecules upon stimulation in vitro and in vivo.

NKT cells express both NK cell-associated markers and TCR. Classically, these NK1.1+TCRalphabeta+ cells have been described as being either CD4+CD8- or CD4-CD8-. Most NKT cells interact with the nonclassical MHC class I molecule CD1 through a largely invariant Valpha14-Jalpha281 TCR chain in conjunction with either a Vbeta2, -7, or -8 TCR chain. In the present study, we describe the presence of significant numbers of NK1.1+TCRalphabeta+ cells within lymphokine-activated killer cell cultures from wild-type C57BL/6, CD1d1-/-, and Jalpha281-/- mice that lack classical NKT cells. Unlike classical NKT cells, 50-60% of these NK1.1+TCRalphabeta+ cells express CD8 and have a diverse TCR Vbeta repertoire. Purified NK1.1-CD8alpha+ T cells from the spleens of B6 mice, upon stimulation with IL-2, IL-4, or IL-15 in vitro, rapidly acquire surface expression of NK1.1. Many NK1.1+CD8+ T cells had also acquired expression of Ly-49 receptors and other NK cell-associated molecules. The acquisition of NK1.1 expression on CD8+ T cells was a particular property of the IL-2Rbeta+ subpopulation of the CD8+ T cells. Efficient NK1.1 expression on CD8+ T cells required Lck but not Fyn. The induction of NK1.1 on CD8+ T cells was not just an in vitro phenomenon as we observed a 5-fold increase of NK1.1+CD8+ T cells in the lungs of influenza virus-infected mice. These data suggest that CD8+ T cells can acquire NK1.1 and other NK cell-associated molecules upon appropriate stimulation in vitro and in vivo.

Animals↗
PubMed2000

Proton-coupled electron transfer at the Q(o) site: what type of mechanism can account for the high activation barrier?

In Rhodobacter sphaeroides, transfer of the first electron in quinol oxidation by the bc(1) complex shows kinetic features (a slow rate (approx. 1.5 x 10(3)/s), high activation energy (approx. 65 kJ/mol) and reorganization energy, lambda (2.5 V)) that are unexpected from Marcus theory and the distances shown by the structures. Reduction of the oxidized iron-sulfur protein occurs after formation of the enzyme-substrate complex, and involves a H-transfer in which the electron transfer occurs through the approx. 7 A of a bridging histidine forming a H-bond with quinol and a ligand to 2Fe-2S. The anomalous kinetic features can be explained by a mechanism in which the electron transfer is constrained by coupled transfer of the proton. We discuss this in the context of mutant strains with modified E(m,7) and pK for the iron-sulfur protein, and Marcus theory for proton-coupled electron transfer. We suggest that transfer of the second proton and electron involve movement of semiquinone in the Q(o) site, and rotation of the Glu of the conserved -PEWY- sequence. Mutational studies show a key role for the domain proximal to heme b(L). The effects of mutation at Tyr-302 (Tyr-279 in bovine sequence) point to a possible linkage between conformational changes in the proximal domain, and changes leading to closure of the iron-sulfur protein access channel at the distal domain.

Bacterial Proteins↗
PubMed2000

Binding of beta-carbolines and related agents at serotonin (5-HT(2) and 5-HT(1A)), dopamine (D(2)) and benzodiazepine receptors.

A large series of beta-carbolines was examined for their ability to bind at [3H]agonist-labeled 5-HT(2A) serotonin receptors. Selected beta-carbolines were also examined at 5-HT(2C) serotonin receptors, 5-HT(1A) serotonin receptors, dopamine D(2) receptors, and benzodiazepine receptors. Indolealkylamines and phenylisopropylamines were also evaluated in some of these binding assays. The beta-carbolines were found to bind with modest affinity at 5-HT(2A) receptors, and affinity was highly dependent upon the presence of ring substituents and ring saturation. The beta-carbolines displayed little to no affinity for 5-HT(1A) serotonin receptors, dopamine D(2) receptors and, with the exception of beta-CCM, for benzodiazepine receptors. Examples of beta-carbolines, indolealkylamines (i.e. N,N-dimethyltryptamine analogs), and phenylisopropylamines have been previously shown to produce common stimulus effects in animals trained to discriminate the phenylisopropylamine hallucinogen DOM (i.e. 1-(2, 5-dimethoxy-4-methylphenyl)-2-aminopropane) from vehicle. Although the only common receptor population that might account for this action is 5-HT(2A), on the basis of a lack of enhanced affinity for agonist-labeled 5-HT(2A) receptors, as well as on their lack of agonist action in the PI hydrolysis assay, it is difficult to conclude that the beta-carbolines behave in a manner consistent with that of other classical hallucinogens.

Animals↗
PubMed2000

alpha -galactosylceramide-activated Valpha 14 natural killer T cells mediate protection against murine malaria.

Natural killer T (NKT) cells are a unique population of lymphocytes that coexpress a semiinvariant T cell and natural killer cell receptors, which are particularly abundant in the liver. To investigate the possible effect of these cells on the development of the liver stages of malaria parasites, a glycolipid, alpha-galactosylceramide (alpha-GalCer), known to selectively activate Valpha14 NKT cells in the context of CD1d molecules, was administered to sporozoite-inoculated mice. The administration of alpha-GalCer resulted in rapid, strong antimalaria activity, inhibiting the development of the intrahepatocytic stages of the rodent malaria parasites Plasmodium yoelii and Plasmodium berghei. The antimalaria activity mediated by alpha-GalCer is stage-specific, since the course of blood-stage-induced infection was not inhibited by administration of this glycolipid. Furthermore, it was determined that IFN-gamma is essential for the antimalaria activity mediated by the glycolipid. Taken together, our results provide the clear evidence that NKT cells can mediate protection against an intracellular microbial infection.

Animals↗
PubMed2000

Specificity and efficiency of Cre-mediated recombination in Emx1-Cre knock-in mice.

Emx1 is a mouse homologue of the Drosophila homeobox gene empty spiracles and its expression is restricted to the neurons in the developing and adult cerebral cortex and hippocampus. We reported previously the creation of a line of transgenic mice in which the cre gene was placed directly downstream of the putative Emx1 promoter using ES cell technology. We showed that Cre protein was present in the cerebral cortex of the transgenic mice and was able to mediate loxP-specific recombination in vitro. In the present study, the specificity and efficiency of the cre-mediated recombination were determined using three independent lines of reporter mice and a combination of histochemical staining, neuronal culture, and Southern detection of the genomic DNA. Our results showed that the recombination was highly efficient in all three lines of reporter mice tested and confirmed that the deletion was restricted to the neurons in the cerebral cortex and hippocampus. Furthermore, we have determined that the recombination efficiency in the cerebral cortex was 91%. Our results suggest that Emx1 is not expressed in every neuron in the developing and adult cerebral cortex. This line of cre mice should contribute to the studies of cortical development and plasticity.

Animals↗
PubMed2000

Localization of C-terminal domains required for the maximal activity or for determination of substrate preference of maize branching enzymes.

Previous analysis of a chimeric enzyme mBEII-IBspHI, in which the C-terminal 229 amino acids of maize endosperm branching enzyme isoform II (mBEII) are replaced by the corresponding 284 amino acids of isoform I (mBEI), suggested that the carboxyl terminus of maize branching enzymes may be involved in catalytic efficiency and substrate preference. In the present study, additional hybrids of mBEI and mBEII were generated and expressed in Escherichia coli BL21 (DE3) to dissect the structure/function relationships of the C-terminal regions of maize branching enzymes. A truncated form of purified mBEII-IBspHI, which lacks the C-terminal 58 amino acids, retained similar levels of V(max) in branching activity, K(m) for reduced amylose AS 320, and substrate preference for amylose than amylopectin when compared to mBEII-IBspHI. This indicates that the C-terminal extension derived from mBEI is not required for either catalysis or substrate preference. However, deletion of an additional 87 amino acids from the carboxyl terminus resulted in complete loss of activity. Replacement of the deleted C-terminal additional 87 amino acids with the corresponding 79 amino acids from mBEII restored 25% of the mBEII-IBspHI branching activity without altering substrate preference. It thus appears that a C-terminal region encompassing Leu649-Asp735 of mBEII-IBspHI is required for maximum catalytic efficiency. Another C-terminal region, residues Gln510-Asp648, of mBEII-IBspHI (Gln476-Asp614 of mBEI) may be involved in substrate-preference determination.

1,4-alpha-Glucan Branching Enzyme↗
PubMed2000

A nanoplotter with both parallel and serial writing capabilities

The development of an eight-pen nanoplotter capable of doing parallel dip-pen nanolithography (DPN) is reported. Because line width and patterning speed in DPN are independent of contact force, only one of the tips in the parallel writing mode (the "imaging" tip) has a feedback system to monitor tip position and to write the pattern; all other tips reproduce what occurs at the imaging tip in a passive fashion. Proof-of-concept experiments that demonstrate eight-pen parallel writing, ink and rinsing wells, and "molecular corralling" via a nanoplotter-generated structure are reported.

Journal Article↗
PubMed2000

Relative contributions of distinct MHC class I-dependent cell populations in protection to tuberculosis infection in mice.

A necessary role for cytotoxic T lymphocytes in protection against Mycobacterium tuberculosis (MTB) has been suggested by studies of the beta2-microglobulin-deficient mouse, which is unable to present antigens through MHC class I and class I-like molecules and invariably succumbs early after infection. To identify the relative contributions of distinct putative MHC class I-dependent cell populations in protection against tuberculosis, we compared a variety of gene-disrupted mouse strains for susceptibility to MTB infection. Among the strains tested, the most susceptible mice, as measured by survival time and bacterial loads, were the beta2-microglobulin(-/-), followed by transporter associated with antigen processing deficient (TAP1(-/-)), CD8alpha(-/-), perforin(-/-), and CD1d(-/-) mice. These findings indicated that (i) CD8(+) T cells contribute to protection against MTB, and their protective activity is only partially dependent on perforin; (ii) beta2-microglobulin-dependent T cell populations distinct from CD8(+) T cells also contribute to anti-MTB immunity; and (iii) protective immune mechanisms are predominantly TAP-dependent, although TAP-independent mechanisms also contribute to protection. Because CD1d-deficient animals were fully resistant to MTB, other TAP-independent mechanisms must contribute to protection. We suggest here that both classical and nonclassical MHC class I-restricted T cells, distinct from CD1d-restricted cells, may be involved in protective immune responses against tuberculosis.

Animals↗
PubMed2000

ATP synthases in the year 2000: evolving views about the structures of these remarkable enzyme complexes.

This introductory article briefly summarizes how our views about the structural features of ATP synthases (F0F1) have evolved over the past 30 years and also reviews some of our current views in the year 2000 about the structures of these remarkably unique enzyme complexes. Suffice it to say that as we approach the end of the first year of this new millinium, we can be conservatively confident that we have a reasonably good grasp of the overall "low-resolution" structural features of ATP synthases. Electron microscopy techniques, combined with the tools of biochemistry, molecular biology, and immunology, have played the leading role here by identifying the headpiece, basepiece, central stalk, side stalk, cap, and in the mitochondrial enzyme, the collar around the central stalk. We can be reasonably confident also that we have a fairly good grasp of much of the "high-resolution" structural features of both the F1 moiety comprised of fives subunit types (alpha, beta, gamma, delta, and epsilon) and parts of the F0 moiety comprised of either three (E. coli) or at least ten (mitochondria) subunit types. This information acquired in several different laboratories, either by X-ray crystallography or NMR spectroscopy, includes details about the active site and subunit relationships. Moreover, it is consistent with recently reported data that the F1 moiety may be an ATP driven motor, which, during ATP synthesis, is driven in reverse by the electrochemical proton gradient generated by the electron transport chain. The real structural challenges of the future are to acquire at high resolution "complete" ATP synthase complexes representative of different stages of the catalytic cycle during ATP synthesis and representative also of key regulatory states.

Crystallography, X-Ray↗
PubMed2000

ATP synthases in the year 2000: defining the different levels of mechanism and getting a grip on each.

ATP synthases are unusually complex molecules, which fractionate most readily into two major units, one a water soluble unit called F(1) and the other a detergent soluble unit called F(0). In almost all known species the F(1) unit consists of 5 subunit types in the stoichiometric ratio alpha(3)beta(3)gammadeltaepsilon while the F(0) unit contains 3 subunit types (a, b, and c) in E. coli, and at least 10 subunit types (a, b, c, and others) in higher animals. It is now believed by many investigators that during the synthesis of ATP, protons derived from an electrochemical gradient generated by an electron transport chain are directed through the F(0) unit in such a way as to drive the rotation of the single gamma subunit, which extends from an oligomeric ring of at least 10 c subunits in F(0) through the center of F(1). It is further believed by many that the rotating gamma subunit, by interacting sequentially with the 3 alphabeta pairs of F(1) (360 degrees cycle) in the presence of ADP, P(i), and Mg++, brings about via "power strokes" conformational/binding changes in these subunits that promote the synthesis of ATP and its release on each alphabeta pair. In support of these views, studies in several laboratories either suggest or demonstrate that F(0) consists in part of a proton gradient driven motor while F(1) consists of an ATP hydrolysis driven motor, and that the gamma subunit does rotate during F(1) function. Therefore, current implications are that during ATP synthesis the former motor drives the latter in reverse via the gamma subunit. This would suggest that the process of understanding the mechanism of ATP synthases can be subdivided into three major levels, which include elucidating those chemical and/or biophysical events involved in (1) inducing rotation of the gamma subunit, (2) coupling rotation of this subunit to conformational/binding changes in each of the 3 alphabeta pairs, and (3) forming ATP and water (from ADP, P(i), and Mg(++)) and then releasing these products from each of the 3 catalytic sites. Significantly, it is at the final level of mechanism where the bond breaking/making events of ATP synthesis occur in the transition state, with the former two levels of mechanism setting the stage for this critical payoff event. Nevertheless, in order to get a better grip in this new century on how ATP synthases make ATP and then release it, we must take on the difficult challenge of elucidating each of the three levels of mechanism.

Adenosine Triphosphate↗
PubMed2000

Validity of measures of cognitive processes and general ability for learning and performance on highly complex computerized tutors: is the g factor of intelligence even more general?

Theoretical arguments and analyses from 2 studies provide compelling evidence that computerized measures of information-processing skills and abilities are highly useful supplements to more traditional, paper-based measures of general mental ability for predicting individuals' capacity to learn from and perform on highly challenging, multifaceted tutors. These tutors were designed to emulate learning and performance in complex, real-world settings. Hierarchical confirmatory factor analysis provided evidence that a general, higher order factor model with general ability at the apex could quite adequately and singularly account for the individual-differences data, both traditional and cognitive-process measures. Results are interpreted in light of the utility and generality of human cognitive abilities.

Cognition↗
PubMed2000

Natural killer cells determine the outcome of B cell-mediated autoimmunity.

Natural killer (NK) cells can affect the outcome of adaptive immune responses. NK cells, but not NK1.1+T cells, were found to participate in the development of myasthenia gravis (a T cell-dependent, B cell- and antibody-mediated autoimmune disease) in C57BL/6 mice. The requirement for NK cells was reflected by the lack of a type I helper T cell response and antibodies to the acetylcholine receptor in both NK1.1+ cell-depleted and NK cell-deficient IL-18-/- mice. These findings establish a previously unrecognized link between NK cells and autoreactive T and B cells.

Amino Acid Sequence↗