Quantum phase of induced dipoles moving in a magnetic field.
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Journal Article↗
Biomedical subjects
X Wei
Publications and source records attributed to X Wei.
Simultaneous determination of theophylline, enoxacin and ciprofloxacin in human plasma and saliva by high-performance liquid chromatography.
A simple reversed-phase high-performance liquid chromatographic method has been developed for the simultaneous determination of theophylline, ciprofloxacin and enoxacin in plasma and saliva. The biological fluid samples were extracted with methylene chloride-isopropyl alcohol prior to isocratic chromatography on a Waters C18 mu Bondapak column. Ultraviolet detection was carried out at 268 nm. The assay is linear for ciprofloxacin and enoxacin (0.05-10 micrograms/ml), and theophylline (0.1-20 micrograms/ml). The assay can be used to investigate the interaction of these two fluoroquinolones with theophylline.
Anti-Infective Agents↗
Use of alpha-N,N-bis[carboxymethyl]lysine-modified peroxidase in immunoassays.
Horseradish peroxidase was activated by periodate oxidation of the carbohydrate moiety and then modified by the covalent attachment of alpha-N,N-bis[carboxyethyl]lysine (CM-Lys) by reductive alkylation using sodium cyanoborohydride. The resultant CM-Lys peroxidase was charged with nickel ions and then used as a specific labeling reagent for histidine-tagged recombinant proteins. This labeling method was effective for proteins that are soluble or insoluble in the absence of chaotropic agents. The labeled proteins were very effective in direct sandwich enzyme-linked immunosorbent assay for detecting antibodies against the protein in sera as demonstrated by assays for antibodies to such diverse viral proteins as hepatitis B surface and core proteins, hepatitis C core and helicase protein (NS3), and retroviral core proteins.
Alkylation↗
Spin dynamics of triplet photoexcitations in C60: Evidence for a dynamic Jahn-Teller effect.
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Journal Article↗
Characterization of the independent and combined effects of two inhibitors on oxidative drug metabolism in rat liver microsomes.
To evaluate how two inhibitors influence oxidative drug metabolism, this study investigated the inhibitory effects of mexiletine with cimetidine and mexiletine with lidocaine, both individually and in combination, on the oxidative metabolism of two probe substrates, aminopyrine and aniline in rat liver microsomes. Mexiletine was a competitive inhibitor of aminopyrine N-demethylation, whereas cimetidine was a mixed type of inhibitor (Ki = 2.00 +/- 0.04 and 0.20 +/- 0.02 mM, respectively). For aniline hydroxylation, mexiletine exhibited a mixed type of inhibition, whereas lidocaine was a noncompetitive inhibitor (Ki = 0.60 +/- 0.07 and 8.50 +/- 0.12 mM, respectively). The combined inhibition of either mexiletine with cimetidine or mexiletine with lidocaine on aminopyrine and aniline metabolism was close to the fully additive effects of the individual compounds when their individual concentrations were below a 2-fold Ki concentration, regardless of the apparent kinetic inhibition type. The combined inhibition was less than fully additive when the individual concentrations were twice the Ki or above. These results demonstrate that, when two inhibitors of oxidative drug metabolism are combined, both the Ki values and the concentrations of inhibitors play important roles in determining the extent of additive inhibition of enzyme activity.
Aminopyrine N-Demethylase↗
Enzymatic characterisation of recombinant murine inducible nitric oxide synthase.
A complementary DNA (cDNA) encoding murine inducible nitric oxide synthase was cloned from activated J774 macrophages. Expression of this cDNA in a baculovirus-insect cell system allowed comparison of the recombinant enzyme with the native homologue. Western blot analysis of activated J774 and baculovirus-infected insect cell cytosols demonstrated reactivity against a protein of 135 kDa. Kinetic studies on the recombinant and native enzymes revealed an absolute requirement for L-arginine and NADPH in order to achieve full activity. In addition, both enzymes were found to have similar maximum velocities and Km values for these two substrates. The nitric oxide synthase antagonists N-guanidino monomethyl L-arginine and N-iminoethyl L-ornithine inhibited both enzymes at a similar rate. Furthermore, comparable concentrations of inhibitor were required to achieve half maximal enzyme inhibition. These results indicate that recombinant inducible NO synthase appears to be pharmacologically indistinguishable from the native enzyme.
Amino Acid Oxidoreductases↗
Voltage-dependent inactivation in a cardiac-skeletal chimeric calcium channel.
The loci for inactivation in calcium channel proteins are unknown. Mechanisms for inactivation may be distributed across Ca2+ channel subunits and appear to be complex, multiple and interacting. We took advantage of the properties of chimeras, constructed between cardiac (H4) and skeletal muscle (Sk4) calcium channel alpha 1 subunits to study the molecular mechanism of inactivation in L-type calcium channels. Sk1H3, a chimeric construct of these two L-type calcium channels, was expressed in Xenopus oocytes in the absence of auxiliary subunits. Sk1H3 incorporated repeat I from skeletal muscle alpha 1 and repeats II, III, IV from heart alpha 1 subunit. Sk1H3 inactivated faster (tau = 300 ms) and more fully than the wild-type H4 with Ba2+ ions as the charge carrier. Thus, inactivation of Sk1H3 was 90% complete after a 5-s conditioning pulse at +20 mV while inactivation of H4 was only 37% complete. Sk1H3 inactivation also developed at more negative potentials with E0.5 = -15 mV as compared to E0.5 = -5 mV for H4. In the presence of external calcium ions, the extent of inactivation significantly increased from 37 to 83% for H4 while inactivation of Sk1H3 was only slightly increased. Inactivation with Ba2+ as the charge carrier was confirmed at the single- channel level where averaged single-channel ensembles showed a similar rate of inactivation. Collectively, these observations demonstrate that Sk1H3 inactivation appears to have a prominent voltage-dependent component. Whether Sk1H3 inactivation involves interactions within repeat I alone or interactions between repeat I and site(s) located in the three other repeats of the alpha 1 subunit has yet to be determined.
Amino Acid Sequence↗
Probing the structure of influenza B hemagglutinin using site-directed mutagenesis.
The crystal structure of the hemagglutinin (HA) of influenza virus A/Aichi/68 (H3N2) from the X-31 reassortant virus was reported in 1981, but as yet there are no X-ray diffraction structures for hemagglutinins of other types or even subtypes of influenza virus. We have used site-directed mutagenesis to probe the structure of the hemagglutinin of influenza B/Hong Kong/8/73. We investigated a region in the globular head domain that is helical in the influenza A HA structure, targeting sidechains that in the H3 HA point toward solvent (Thr196) or into the receptor-binding pocket (Gln197). None of the mutations affected hemagglutination activity, but mutations T196P or Q1971 eliminated binding of a monoclonal antibody. The data suggest that this region of the influenza B HA forms a surface structure different from the alpha-helix of the influenza A HA structure and that it accounts for much of the antigenic activity of influenza B HA.
Amino Acid Sequence↗
Viral dynamics in human immunodeficiency virus type 1 infection.
The dynamics of HIV-1 replication in vivo are largely unknown yet they are critical to our understanding of disease pathogenesis. Experimental drugs that are potent inhibitors of viral replication can be used to show that the composite lifespan of plasma virus and virus-producing cells is remarkably short (half-life approximately 2 days). Almost complete replacement of wild-type virus in plasma by drug-resistant variants occurs after fourteen days, indicating that HIV-1 viraemia is sustained primarily by a dynamic process involving continuous rounds of de novo virus infection and replication and rapid cell turnover.
Antiviral Agents↗
Corticospinal motor neurons in the adult rat: degeneration after intracortical axotomy and protection by ciliary neurotrophic factor (CNTF).
Little is known about the neurotrophic factors that may regulate maintenance, growth, and/or repair of corticospinal motor neurons (CSMN) in the developing or the adult mammal. We have developed an adult rat in vivo model of CSMN injury involving (i) bilateral prelabeling of CSMN with a cervical spinal cord injection of cholera toxin B subunit (CTB), (ii) unilateral axotomy close to the cell bodies by an intracortical lesion between cell layer V and the corpus callosum, and (iii) implantation of a continuous infusion device in the cortical parenchyma near the lesion. Two weeks later, coronal sections of the cortex are immunostained for CTB, and CTB-stained neurons are counted over defined section areas and compared to those on the contralateral (nonlesioned, noninfused) side. CTB-stainable neurons were 30-40% of the control side when the lesion was about 200 microns from the deeper face of the cell layer, and survival increased with increasing lesion depths. The model can be used to assess protective effects of potential CSMN trophic factors. The low survival achieved with the more superficial lesions (200 and 300 microns) was markedly improved by continuous infusion of ciliary neurotrophic factor at 0.1 to 1.0 microgram/day.
Animals↗
Onset of expression of the alpha subunit of Ca2+/calmodulin-dependent protein kinase II and a novel related protein in the developing retina.
Calcium-calmodulin-dependent protein kinase II is an abundant protein in the nervous system and has been associated with many aspects of neuronal function, including events related to synaptic transmission. The purpose of this study is to correlate the onset of expression of this kinase with a specific developmental event in retinal morphogenesis using a monoclonal antibody to the 50-kDa alpha-subunit. Microscopy showed the antigen to be associated with the plexiform layers of the retina. Western blots demonstrated that the onset of expression of the alpha-subunit coincided in time with the initial formation of the plexiform layers. However, the onset of expression of the 50-kDa alpha-subunit was preceded by the earlier embryonic appearance of a related 82.5-kDa antigen that was recognized by the antibody. The amount of this latter protein declined as the amount of the alpha-subunit increased in retinal homogenates. Although this related 82.5 kDa protein disappeared from blots of retinal homogenates after embryonic d 14, it could be detected in concentrated supernatant fractions isolated from the retinae of hatched chicks. Microscopy showed that a subset of retinal cells and their processes contained this antigen in early embryonic chicks. Finally, the 50 kDa alpha-subunit of kinase II and the 82.5 kDa novel antigen were shown to be separable by differential centrifugation.
Animals↗
Alpha-1 subunits of voltage gated Ca2+ channels in the mesencephalon x neuroblastoma hybrid cell line MES23.5.
The identity of alpha 1 subunits from voltage operated Ca2+ channels was determined in the rat/mouse mesencephalon x N18TG2 hybridoma cell line MES23.5, by sequence analysis of reverse transcription-polymerase chain reaction products and antagonist binding. Sequences were derived from the L-(alpha 1D), Q-(alpha 1A) and omega-conotoxin GVIA sensitive N-type (alpha 1B) Ca2+ channel alpha 1 subunits. The amplified fragments, which are homologous to the region between domain III and IV of known alpha 1 subunits, reveal splice variation in the L- and Q-type alpha 1 subunit of MES23.5 cells. The transcripts of alpha 1 subunits in these cells were quantified by RNAase protection assay. The data show the existence of different Ca2+ channel types in a single cell line and may reflect multiple functions of voltage operated Ca2+ channels during growth, differentiation and transmitter release.
Amino Acid Sequence↗
The nuclear matrix: a structural milieu for genomic function.
While significant progress has been made in elucidating molecular properties of specific genes and their regulation, our understanding of how the whole genome is coordinated has lagged behind. To understand how the genome functions as a coordinated whole, we must understand how the nucleus is put together and functions as a whole. An important step in that direction occurred with the isolation and characterization of the nuclear matrix. Aside from the plethora of functional properties associated with these isolated nuclear structures, they have enabled the first direct examination and molecular cloning of specific nuclear matrix proteins. The isolated nuclear matrix can be used for providing an in vitro model for understanding nuclear matrix organization in whole cells. Recent development of high-resolution and three-dimensional approaches for visualizing domains of genomic organization and function in situ has provided corroborative evidence for the nuclear matrix as the site of organization for replication, transcription, and post-transcriptional processing. As more is learned about these in situ functional sites, appropriate experiments could be designed to test molecular mechanisms with the in vitro nuclear matrix systems. This is illustrated in this chapter by the studies of nuclear matrix-associated DNA replication which have evolved from biochemical studies of in vitro nuclear matrix systems toward three-dimensional computer image analysis of replication sites for individual genes.
Animals↗
Dual activation of the cardiac Ca2+ channel alpha 1C-subunit and its modulation by the beta-subunit.
Ca2+ channels are heteromultimeric proteins in which the alpha 1-subunit forms the voltage-dependent Ca(2+)-selective ionic channel. We reported recently that coexpression of the beta-subunit with the cardiac alpha 1-subunit (alpha 1C) facilitates channel opening without affecting either the amplitude or the time course of the gating currents (13). Here we present evidence for the existence of two modes of channel opening. Xenopus oocytes expressing the alpha 1C-subunit alone display two modes of activation as indicated by the double-exponential time course of macroscopic ionic currents and the two open-time distributions of single channels. Coexpression of the beta-subunit potentiates Ca2+ currents by a relative increase of the fast-activating component, an acceleration of the slow component, and a larger proportion of long openings. We propose that multiple modes of gating are encoded in the alpha 1-subunit and that the beta-subunit increases Ca2+ channel opening by favoring a willing mode of gating in which the final transitions leading to channel opening are facilitated. In addition, we show that the carboxy terminus of alpha 1C also modulates the channel-gating behavior.
Animals↗
[Dumbbell like neurinoma at upper cervical vertebra: report of 48 cases].
48 dumbbell like neurinoma at upper cervical vertebra were totally removed operatively and confirmed pathologically. Intermittent pain at neck and occiput limitation of neck movement, and numbness or pain at one or both side limbs were the most common symptoms. In the early stage, the disease was difficalt to recognize. If X-ray film of the cervical vertebra at bioblique position showed an enlarged intervertebral foramen, the diagnosis of neurinoma should be highly considered. MRI could make a definite diagnosis. Vertebral artery angiography is of great value. We also introduced experience in how to protect vertebral artery and respiratory function during operation.
Adolescent↗
Relative potency of mexiletine, lidocaine, and tocainide as inhibitors of rat liver CYP1A1 activity.
Mexiletine and tocainide are lidocaine congeners that share similar chemical structures. Clinical studies suggest that the in vivo inhibitory effect of mexiletine on the CYP1A family of isoforms is substantially greater than that of tocainide. We investigated the inhibitory property of mexiletine, lidocaine, and tocainide on the in vitro activity of the cytochrome P4501A1 (CYP1A1) isozyme in the rat. Hepatic microsomes were prepared from rat livers induced with 3-methylcholanthrene. The rate of ethoxyresorufin-O-dealkylation (EROD) was used as an index of CYP1A1 activity. Vmax and KM of the reactions were determined from Lineweaver-Burk plots. The Ki values for the inhibitors were derived from Dixon plots. Results showed that mexiletine is a competitive inhibitor, lidocaine is a mixed inhibitor, and tocainide is a noncompetitive inhibitor of EROD. The Ki values for mexiletine and tocainide were 0.30 +/- 0.02 mM and 12.4 +/- 0.7 mM, respectively. Two Ki values for lidocaine were determined. They were 0.65 +/- 0.07 mM and 4.1 +/- 1.3 mM, respectively. The relative inhibitory potency of these agents on rat CYP1A1 activity is mexiletine > lidocaine > tocainide. This difference in potency, which is most likely attributable to the change in the chemical composition in the aliphatic chain among the compounds, suggests that these compounds may be useful probes for studying the mechanism of the interaction with the active site of CYP1A1.
Animals↗
Excitons in poly(para-phenylenevinylene).
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Journal Article↗