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X Lin

Publications and source records attributed to X Lin.

At least 343 records · Page 19Linked to original sources
PubMed1996

[A study on the expression of three cytokine-receptors and airway hyperreactivity in asthmatics after specific provocation].

OBJECTIVE: In order to study the role of T and B lymphocytes activation in the pathogenesis of asthma. METHOD: Pulmonary function tests were performed and percentages of three cytokine receptors and the levels of sIL-2R, sIgE and TIgE were measured in 31 allergic asthmatics and 12 healthy subjects before and after specific provocation. RESULTS: It was found that the serum levels of sIL-2R (t = 5,719, 5,647 P < 0.01), TIgE were measured in 31 allergic asthmatics and 12 healthy (t = 6,306, 7,218 P < 0.01) and percentages of CD+23 (chi(2) -23.43, 18.56 P < 0.01) or CD+(25) (chi(2) = 27.59, 15. 28) cells were significantly higher in asthmatics after challenge than those in controls or in asthmatics before challenge as well; There were significantly negative correlations between sIL-2R and FEV1 or sGaw (r = -0.573, -0.426 P < 0.01), whereas positive correlations between sIL-2R and Raw or percent of IL-2R/CD+(25) cells (r = 0.417, 0.532 P < 0.01); TIgE and percent of Fc epsilon R II/CD+(23) cells (r = 0.603 P < 0.01), respectively. CONCLUSION: These findings suggest that T cell activation, increased serum levels of sIL-2R and increased expression of CD+(25) or CD+(23) on cells, may lead to enhanced AHR in allergic asthmatics.

Adult↗
PubMed1995

VP1 and VP2 capsid proteins of Theiler's virus are targets of H-2D-restricted cytotoxic lymphocytes in the central nervous system of B10 mice.

Resistance to Theiler's virus-induced demyelination maps genetically to the MHC class I D region and is associated with up-regulation of class I products and the presence of MHC-restricted virus-specific cytotoxic CD8+ T cells in the CNS. To determine the targets of the cytotoxic response, transfected C57SV (Kb, Db) cells expressing LP (including the leader peptide, VP4, VP2, and VP3 coding sequences), VP4 (including the leader peptide and VP4), VP2, VP3, VP1, or RP (including P2 and P3) were generated. CNS-infiltrating lymphocytes obtained from virus-infected B10, B10.K (Kk, Dk), B10.RBF (Kb, Df). B10.RFB3 (Kf, Db), and B10.RBQ (Kb, Dq) mice were used as effectors. Specific cytotoxicity to the capsid proteins encoded in the LP construct, VP2 and VP1, was demonstrated to be H-2Db region restricted and was mediated by CD8+ T cells. No Kb-restricted virus-specific cytotoxicity response was observed. No specific cytotoxic response against RP-encoded proteins was observed in the CNS of B10 mice. Therefore, both VP1 and VP2 are targets for an H-2D-restricted cytotoxic immune response against Theiler's virus infection in the CNS of infected resistant B10 mice.

Animals↗
PubMed1995

Lysosome-associated membrane protein-1-mediated targeting of the HIV-1 envelope protein to an endosomal/lysosomal compartment enhances its presentation to MHC class II-restricted T cells.

A subset of endogenously synthesized Ags can be processed for class II-restricted presentation, probably through multiple mechanisms. Processing of exogenous Ags for class II-restricted presentation appears to occur in unique endosomal processing compartments with lysosomal characteristics including the presence of the lysosomal membrane protein LAMP-1. Therefore, we attempted to enhance the efficiency of class II-restricted presentation of an endogenous Ag, the HIV-1 envelope (env) protein, by specifically targeting the Ag to class II processing compartments through the pathway followed by LAMP-1. Because the env protein associates tightly with CD4 shortly after synthesis, we first targeted the env protein using a chimeric CD4 protein consisting of the extracellular domain of CD4 and the transmembrane and cytoplasmic domains of LAMP-1. When co-expressed with this chimeric protein, the env protein was efficiently localized to lysosome-like compartments. Enhanced stimulation of env-specific CD4+ T cell clones by APC expressing the env protein and the CD4-LAMP-1 chimera was readily demonstrated in both cytotoxicity assays and proliferation assays. We also targeted the env protein directly as a chimeric protein consisting of the extracellular domain of the env protein and the transmembrane and cytoplasmic domains of LAMP-1. The proliferative response of env-specific CD4+ T cell clones to the env-LAMP-1 chimera was greatly enhanced compared with wild-type env protein, especially when limiting numbers of stimulator cells were used. The enhanced stimulatory capacity of APC expressing LAMP-1-targeted Ags has important implications for vaccine design.

Antigen Presentation↗
PubMed1995

Effect of vibrissae deprivation on follicle innervation, neuropeptide synthesis in the trigeminal ganglion, and S1 barrel cortex plasticity.

Deprivation of vibrissae from an early age causes plasticity in S1 barrel cortex. This method of deprivation is most likely to induce plasticity by altering the balance of primary afferent activity from the deprived and spared vibrissae. To study whether or not induction or expression of this type of plasticity might be affected by follicle nerve injury caused by the deprivation technique, three different methods of detecting nerve injury were used: counting axon numbers in the distal follicle nerve, quantifying morphological changes in axons, and measuring neuropeptide expression in the trigeminal ganglion cells. First, nerves innervating follicles chronically deprived of vibrissae from birth had the same number of myelinated and unmyelinated axons as nerves from normally reared animals. Second, axons innervating deprived follicles showed no morphological changes in myelination or mitochondria characteristic of damaged nerves. Third, the corresponding nerve cell bodies in the trigeminal ganglion did not show upregulation of galanin or neuropeptide Y expression. In contrast, animals receiving mild injury of the follicle nerve endings (by cauterization of the follicle) showed profound changes in axonal myelination and mitochondria and increases in neuropeptide expression. These results imply that vibrissae deprivation does not act by inducing injury of the follicular nerve, suggesting that changes in the balance of follicle nerve activity are the cause of cortical plasticity. Consistent with this notion, a fourth experiment demonstrated that trimming the vibrissae induces cortical plasticity comparable to that induced by complete vibrissae removal.

Afferent Pathways↗
PubMed1995

ENDOR studies of the primary donor cation radical in mutant reaction centers of Rhodobacter sphaeroides with altered hydrogen-bond interactions.

The electronic structure of the cation radical of the primary electron donor was investigated in genetically modified reaction centers of Rhodobacter sphaeroides. The site-directed mutations were designed to add or remove hydrogen bonds between the conjugated carbonyl groups of the primary donor, a bacteriochlorophyll dimer, and histidine residues of the protein and were introduced at the symmetry-related sites L168 His-->Phe, HF(L168), and M197 Phe-->His, FH(M197), near the 2-acetyl groups of the dimer and at sites M160 Leu-->His, LH(M160), and L131 Leu-->His, LH(L131), in the vicinity of the 9-keto carbonyls of the dimer. The single mutants and a complete set of double mutants were studied using EPR, ENDOR, and TRIPLE resonance spectroscopy. The changes in the hydrogen bond situation of the primary donor were accompanied by changes in the dimer oxidation midpoint potential, ranging from 410 to 710 mV in the investigated mutants [Lin, X., Murchison, H. A., Nagarajan, V., Parson, W. W., Williams, J. C. & Allen, J. P. (1994) Proc. Natl. Acad. Sci. U.S.A. 91, 10265-10269]. It was found that the addition or removal of a hydrogen bond causes large shifts of the spin density between the two halves of the dimer. Measurements on double mutants showed that the unpaired electron can be gradually shifted from a localization on the L-half of the dimer to a localization on the M-half, depending on the hydrogen bond situation. As a control, the effects of the different hydrogen bonds on P.+ in the mutant HL(M202), which contains a BChlL-BPheM heterodimer as the primary donor with localized spin on the BChl aL [Bylina, E. J., & Youvan, D. C. (1988) Proc. Natl. Acad. Sci. U.S.A. 85, 7226-7230; Schenck, C. C., Gaul, D., Steffen M., Boxer S. G., McDowell L., Kirmaier C., & Holten D. (1990) in Reaction Centers of Photosynthetic Bacteria (Michel-Beyerle M. E., Ed.) pp 229-238, Springer, Berlin] were studied. In this mutant only small local changes of the spin densities (< or = 10%) in the vicinity of the hydrogen bonds were observed. The effects of the introduced hydrogen bonds on the spin density distribution of the dimer in the mutants are discussed in terms of different orbital energies of the two BChl a moieties which are directly influenced by hydrogen bond formation. The observed changes of the spin density distribution for the double mutants are additive with respect to the single mutations.(ABSTRACT TRUNCATED AT 400 WORDS)

Cations↗
PubMed1995

The kappa-opioid receptor is primarily postsynaptic: combined immunohistochemical localization of the receptor and endogenous opioids.

Antisera were raised against a synthetic peptide corresponding to the carboxyl terminus of the kappa-opioid receptor (KOR1). Specificity of the antisera was verified by staining of COS-7 cells transfected with KOR1 and epitope-tagged KOR1 cDNAs, by recognition by the antisera of proteins on Western blots of both transfected cells and brain tissue, by the absence of staining of both brain tissue and transfected cells after preabsorption of the antisera with the cognate peptide, and on the strong correlation between the distribution of KOR1 immunoreactivity and that of earlier ligand binding and in situ hybridization studies. Results indicate that KOR1 in neurons is targeted into both the axonal and somatodendritic compartments, but the majority of immunostaining was seen in the somatodendritic compartment. In sections from rat and guinea pig brain, prominent KOR1 staining was seen in the ventral forebrain, hypothalamus, thalamus, posterior pituitary, and midbrain. While the staining pattern was similar in both species, distinct differences were also observed. The distribution of preprodynorphin and KOR1 immunoreactivity was complementary in many brain regions, suggesting that KOR1 is poised to mediate the physiological actions of dynorphin. However, the distribution of KOR1 and enkephalin immunoreactivity was complementary in some regions as well. These results suggest that the KOR1 protein is primarily, but not exclusively, deployed to postsynaptic membranes where it mediates the effects of products of preprodynorphin and possibly preproenkephalin.

Amino Acid Sequence↗
PubMed1995

Correlation between multiple hydrogen bonding and alteration of the oxidation potential of the bacteriochlorophyll dimer of reaction centers from Rhodobacter sphaeroides.

The electronic absorption and vibrational Raman spectra of mutant reaction centers from Rhodobacter sphaeroides bearing multiple site-specific mutations near the primary electron donor (P), a bacteriochlorophyll dimer, are reported. These mutations bear double and triple combinations of single-point mutations that alter the H-bonding interactions between histidine residues and the C2- and C9-conjugated carbonyl groups of the primary donor [Mattioli, T.A., Williams, J.C., Allen, J.P., & Robert, B. (1994) Biochemistry 33, 1636-1643] and change the donor redox midpoint potential from 410 to 765 mV compared to 505 mV for wild type [Lin, X., Murchison, H.A., Nagarajan, V., Parson, W.W., Williams, J.C., & Allen, J.P. (1994) Proc. Natl. Acad. Sci. U.S.A. 91, 10265-10269]. Near-infrared Fourier transform Raman spectroscopy was used to determine the changes in H-bonding interactions of the primary donor in these multiple mutants. The Fourier transform Raman spectra of the mutants exhibit the predicted changes in hydrogen bond interactions of the P carbonyl groups with the protein, and they are consistent with the designed mutations. Moreover, the Raman data verify that the H-bonds formed or broken in the multiple mutants are similar in strength to those observed in the corresponding single mutants. A correlation was observed between the change in P/P.+ redox midpoint potential and the total change in H-bonding interaction energy (from -207 to 364 meV relative to wild type) as gauged by the estimated enthalpy of each H-bond formed or broken on the four conjugated carbonyls of the primary donor. Only minor changes were observed in the optical spectra of the mutant reaction centers, indicating that the addition of H-bonds from histidines has little effect in destabilizing the first electronic excited state of the dimer relative to the ground state. However a blue shift in the dimer absorption band at ca. 890 nm at 20 K was associated with the removal of the H-bond to the C2 acetyl carbonyl group via His L168. A red shift of the oxidized dimer band at ca. 1250 nm was associated with the formation of each H-bond to the C9 keto carbonyl groups.

Hydrogen Bonding↗
PubMed1995

Effect of point mutations on the kinetics and the inhibition of human immunodeficiency virus type 1 protease: relationship to drug resistance.

Mutations of human immunodeficiency virus type 1 (HIV-1) protease at four positions, Val82, Asp30, Gly48, and Lys45 were analyzed for the resulting effects on kinetics and inhibition. In these mutants, Val82 was substituted separately by Asn, Glu, Ala, Ser, Asp, and Gln; Asp30 was individually substituted by Phe or Trp; Gly48 by His, Asp, and Tyr, respectively; and Lys45 by Glu. By examination of the inhibition of a single inhibitor, the differences in Ki values between the native and mutant enzymes can range from very large to insignificant even for the mutants with substitutions at the same position. By examination of a single mutant enzyme, the same broad range of Ki changes was observed for a group of inhibitors: Thus, how much the inhibition changes from the wild-type enzyme to a mutant is dependent on both the mutation and the inhibitor. The examination of Ki changes of inhibitors with closely related structures binding to Val82 mutants also reveals that the change of inhibition involves subsites in which Val82 is not in direct contact, indicating a considerable flexibility of the conformation of HIV protease. For the catalytic activities of the mutants, the kcat and Km values of many Val82 mutants and a Lys45 mutant are comparable to the native enzyme. Surprisingly, Gly48 mutations produce enzymes with catalytic efficiency superior to that of the wild-type enzyme by as much as 10-fold. Modeling of the structure of the mutants suggests that the high catalytic efficiency of some substrates is related to an increase of rigidity of the flap region of the mutants. The examination of the relative changes of inhibition and catalysis of mutants suggests that some of the Val82 and Gly48 mutants are potential resistance mutants. However, the resistance is specific with respect to individual inhibitors.

Amino Acid Sequence↗
PubMed1995

Rearranging the domains of pepsinogen.

Most eukaryotic aspartic protease zymogens are synthesized as a single polypeptide chain that contains two distinct homologous lobes and a pro peptide, which is removed upon activation. In pepsinogen, the pro peptide precedes the N-terminal lobe (designated pep) and the C-terminal lobe (designated sin). Based on the three-dimensional structure of pepsinogen, we have designed a pepsinogen polypeptide with the internal rearrangement of domains from pro-pep-sin (native pepsinogen) to sin-pro-pep. The domain-rearranged zymogen also contains a 10-residue linker designed to connect sin and pro domains. Recombinant sin-pro-pep was synthesized in Escherichia coli, refolded from 8 M urea, and purified. Upon acidification, sin-pro-pep autoactivates to a two-chain enzyme. However, the emergence of activity is much slower than the conversion of the single-chain zymogen to a two-chain intermediate. In the activation of native pepsinogen and sin-pro-pep, the pro region is cleaved at two sites between residues 16P and 17P and 44P and 1 successively, and complete activation of sin-pro-pep requires an additional cleavage at a third site between residues 1P and 2P. In pepsinogen activation, the cleavage of the first site is rate limiting because the second site is cleaved more rapidly to generate activity. In the activation of sin-pro-pep, however, the second site is cleaved slower than the first, and cleavage of the third site is the rate limiting step.(ABSTRACT TRUNCATED AT 250 WORDS)

Amino Acid Sequence↗
PubMed1995

An NMR and spin label study of the effects of binding calcium and troponin I inhibitory peptide to cardiac troponin C.

The paramagnetic relaxation reagent, 4-hydroxy-2,2,6,6-tetramethylpiperidinyl-1-oxy (HyTEMPO), was used to probe the surface exposure of methionine residues of recombinant cardiac troponin C (cTnC) in the absence and presence of Ca2+ at the regulatory site (site II), as well as in the presence of the troponin I inhibitory peptide (cTnIp). Methyl resonances of the 10 Met residues of cTnC were chosen as spectral probes because they are thought to play a role in both formation of the N-terminal hydrophobic pocket and in the binding of cTnIp. Proton longitudinal relaxation rates (R1's) of the [13C-methyl] groups in [13C-methyl]Met-labeled cTnC(C35S) were determined using a T1 two-dimensional heteronuclear single- and multiple-quantum coherence pulse sequence. Solvent-exposed Met residues exhibit increased relaxation rates from the paramagnetic effect of HyTEMPO. Relaxation rates in 2Ca(2+)-loaded and Ca(2+)-saturated cTnC, both in the presence and absence of HyTEMPO, permitted the topological mapping of the conformational changes induced by the binding of Ca2+ to site II, the site responsible for triggering muscle contraction. Calcium binding at site II resulted in an increased exposure of Met residues 45 and 81 to the soluble spin label HyTEMPO. This result is consistent with an opening of the hydrophobic pocket in the N-terminal domain of cTnC upon binding Ca2+ at site II. The binding of the inhibitory peptide cTnIp, corresponding to Asn 129 through Ile 149 of cTnI, to both 2Ca(2+)-loaded and Ca(2+)-saturated cTnC was shown to protect Met residues 120 and 157 from HyTEMPO as determined by a decrease in their measured R1 values. These results suggest that in both the 2Ca(2+)-loaded and Ca(2+)-saturated forms of cTnC, cTnIp binds primarily to the C-terminal domain of cTnC.

Amino Acid Sequence↗
PubMed1995

Effect of glucose on the respiratory burst of circulating neutrophils from asthmatics.

The respiratory burst is dependent on a source of glucose. We wished to investigate the effect of glucose on the superoxide production of circulating neutrophils. Superoxide production of neutrophils was significantly enhanced by glucose concentration of from 1 to 50 mmole/liter in the medium. The neutrophils from asthmatics in both the acute and remission phases showed greater production of superoxide than those of controls. When the neutrophils were made to undergo the respiratory burst, initially in the absence of glucose, and thereafter in the presence of 5 and 20 mmole/liter glucose, the rate of superoxide formation with higher glucose medium was decreased in the control cells but significantly increased in the cells of the acute asthmatics in remission. It is concluded that glucose as an energy source is potentially critical in determining the rate of the respiratory burst and that the neutrophils from asthmatic subjects in some way have an enhanced uptake or metabolism of this substrate. Glycemic status may then have some role in determining the amount of superoxide production, and therefore airway inflammation, in asthma.

Adolescent↗
PubMed1995

Thermopsin.

Explore the source record for details and available documents.

Amino Acid Sequence↗
PubMed1995

Dihydropyridines and verapamil inhibit voltage-dependent K+ current in isolated outer hair cells of the guinea pig.

Dihydropyridines and verapamil are widely used as blockers of voltage-dependent Ca++ channels. In this work we show that these compounds can have a direct blocking action on a class of voltage-activated potassium channels. Voltage-dependent whole-cell currents were recorded from isolated guinea-pig outer hair cells (OHCs) under conditions such that the free Ca++ concentration in both the internal and external solutions was minimized. A substantial Ca(++)-independent K+ current was revealed by this procedure. Both conventional K+ and Ca++ channel ligands inhibited this current. The order of potency (in terms of the half inhibitory concentrations (IC50) of channel inhibitors) was: nimodipine (6 microM) > Bay K 8644 (8 microM) > verapamil (11 microM) > 4-aminopyridine (22 microM) > nifedipine (32 microM) > quinine (49 microM) > TEA (10236 microM). Except for verapamil, these channel ligands reduced the size of the K+ currents without much alteration of the time course of the currents. In contrast, verapamil caused a more than 10-fold increase in the apparent inactivation rate of the K+ currents without significantly altering the activation of the currents. The observation that relatively low concentrations of calcium channel ligands can directly inhibit potassium currents in isolated OHCs indicates that caution should be taken when these pharmacological agents are used as tools for studying cochlear hair cell physiology.

3-Pyridinecarboxylic acid, 1,4-dihydro-2,6-dimethy↗
PubMed1995

Carnitine palmitoyltransferase modulation of hepatic fatty acid metabolism and radio-HPLC evidence for low ketogenesis in neonatal pigs.

A neonatal piglet model was used to study hepatic fatty acid metabolism during the early postnatal period. Hepatocytes were isolated from pigs at birth or after 24 h, in fed or unfed states (n = 4 pigs/group). Cells were incubated with 1 mmol/L [1-(14)C]-octanoate (C8) or -palmitate (C16) in the presence or absence of 1 mmol/L L-carnitine, carnitine plus tetradecylglycidic acid (TDGA; 10 mumol/L) or carnitine plus glucagon (0.5 microgram/L). Accumulation of radiolabel [nmol/(h. 10(6) cells)] in CO2 and acid-soluble products (ASP) was higher (3.5- and 4.5-fold, respectively) from C8 than from C16 (P < 0.0001). Glucagon, carnitine and TDGA had no effect on the oxidation of C8 (P > 0.1). Carnitine addition tended to increase C16 flux to ASP [from 5.3 to 7.6 nmol/(h. 10(6) cells); P < 0.1], whereas carnitine plus TDGA decreased flux (from 7.6 to 2.1; P < 0.001). Esterified products accounted for 70% of metabolized label in control C16 incubations; this was reduced to 62% by carnitine (P < 0.05) and increased to 80% by the addition of carnitine plus TDGA (P < 0.0001). The 1-(14)C flux to CO2 in cells from 24-h-old unfed piglets was 47% lower than from fed pigs (P < 0.01) but 28% higher than in pigs at birth. Radiolabel contained in ASP and total metabolized label were 48% lower from unfed pigs compared with the piglets at birth and 24-h-old fed pigs (P < 0.01) and were paralleled by changes in oxygen consumption.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1995

Blood coagulation and fibrinolysis at rest and in response to maximal exercise before and after a physical conditioning programme.

Twenty-five young subjects were divided into experimental (n = 13) and control (n = 12) groups in order to examine the acute and chronic effects of exercise on blood coagulation and fibrinolysis. Blood coagulation and fibrinolysis variables were ascertained in both groups before and after a physical conditioning programme both at rest and following maximal exercise. The experimental group exercised for 12 weeks [30 min, 3 x week at 70% (6 weeks) and 80% (6 weeks) of maximum heart rate]. The control group maintained normal activity patterns. Significant activation (P < 0.05) of blood coagulation was observed in response to maximal exercise before and after the conditioning programme in both groups in activated partial thromboplastin time (APTT), thrombin clotting time (TCT), factor VIII procoagulant activity (FVIII PA) and factor VIII antigen (FVIII A). Likewise, blood plasminogen activator showed a significant increase (P < 0.05) in response to maximal exercise before and after conditioning in both groups. Although VO2 max following the conditioning programme was significantly increased in the exercise group versus control, no significant changes (P > 0.05) were observed in either group in blood coagulation and fibrinolysis parameters at rest or in response to maximal exercise. It is concluded that maximal exercise transiently accelerates blood coagulation and activates blood fibrinolytic activity, however physical conditioning appears not to influence the haemostatic and fibrinolytic systems at rest or in response to maximal exercise.

Adult↗
PubMed1995

DQCAR microsatellite polymorphisms in three selected HLA class II-associated diseases.

DQCAR is a very polymorphic CA repeat microsatellite located between the HLA DQA1 and DQB1 gene. Previous studies have shown that specific DQCAR alleles are in tight linkage disequilibrium with known HLA DR-DQ haplotypes. Of special interest was the fact that haplotypes containing long CA repeat alleles (DQCAR > 111) were generally more polymorphic within and across ethnic groups. In these latter cases, several DQCAR alleles were found even in haplotypes containing the same flanking DQA1 and DQB1 alleles. In this work, three HLA class II associated diseases were studied using the DQCAR microsatellite. The aim of this study was to test if DQCAR typing could distinguish haplotypes with the same DRB1, DQA1 and DQB1 alleles in control and affected individuals. To do so, patients with selected HLA DR-DQ susceptibility haplotypes were compared with HLA DR and DQ matched controls. This included: Norwegian subjects with Celiac disease and the HLA DRB1*0301, DQA1*05011, DQB1*02 haplotype; Japanese subjects with Type 1 (insulin-dependent) Diabetes Mellitus and the HLA DRB1*0405, DQA1*0302, DQB1*0401 haplotype; and French patients with corticosensitive Idiopathic Nephrotic Syndrome and the HLA DRB1*0701, DQA1*0201, DQB1*0202 haplotype. These specific haplotypes were selected from our earlier work to include one haplotype bearing a short DQCAR allele (celiac disease and DR3,DQ2-DQCAR99) and two haplotypes bearing long DQCAR alleles (Diabetes Mellitus and DR4,DQ4-DQCAR 113 or 115 Idiopathic Nephrotic syndrome and DR7,DQ2-DQCAR 111-121). Additional DQCAR diversity was found in both control and patients bearing haplotypes with long CA repeat alleles. The results indicate that DQCAR typing did not improve specificity in combination with high resolution DNA HLA typing as a marker for these three disorders.

Base Sequence↗