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M Li

Publications and source records attributed to M Li.

At least 343 records · Page 19Linked to original sources
PubMed2000

The aspartic proteinase from Saccharomyces cerevisiae folds its own inhibitor into a helix.

Aspartic proteinase A from yeast is specifically and potently inhibited by a small protein called IA3 from Saccharomyces cerevisiae. Although this inhibitor consists of 68 residues, we show that the inhibitory activity resides within the N-terminal half of the molecule. Structures solved at 2.2 and 1.8 A, respectively, for complexes of proteinase A with full-length IA3 and with a truncated form consisting only of residues 2-34, reveal an unprecedented mode of inhibitor-enzyme interactions. Neither form of the free inhibitor has detectable intrinsic secondary structure in solution. However, upon contact with the enzyme, residues 2-32 become ordered and adopt a near-perfect alpha-helical conformation. Thus, the proteinase acts as a folding template, stabilizing the helical conformation in the inhibitor, which results in the potent and specific blockage of the proteolytic activity.

Amino Acid Sequence↗
PubMed2000

Minocycline inhibits caspase-1 and caspase-3 expression and delays mortality in a transgenic mouse model of Huntington disease.

Huntington disease is an autosomal dominant neurodegenerative disease with no effective treatment. Minocycline is a tetracycline derivative with proven safety. After ischemia, minocycline inhibits caspase-1 and inducible nitric oxide synthetase upregulation, and reduces infarction. As caspase-1 and nitric oxide seem to play a role in Huntington disease, we evaluated the therapeutic efficacy of minocycline in the R6/2 mouse model of Huntington disease. We report that minocycline delays disease progression, inhibits caspase-1 and caspase-3 mRNA upregulation, and decreases inducible nitric oxide synthetase activity. In addition, effective pharmacotherapy in R6/2 mice requires caspase-1 and caspase-3 inhibition. This is the first demonstration of caspase-1 and caspase-3 transcriptional regulation in a Huntington disease model.

Animals↗
PubMed2000

Applications of display technology in protein analysis.

Display technology refers to a collection of methods for creating libraries of modularly coded biomolecules that can be screened for desired properties. It has become a routine tool for enriching molecular diversity and producing novel types of proteins. The combination of an ever-increasing variety of libraries of modularly coded protein complexxes with the development of innovative approaches to select a wide array of desired properties has facilitated large-scale analyses of protein-protein/protein-substrate interactions, rapid isolation of antibodies (or antibody mimetics) without immunization, and function-based protein analysis. Several practical and theoretical challenges remain to be addressed before display technology can be readily applied to proteomic studies.

Animals↗
PubMed2000

Interactions of Janus Green B with double stranded DNA and the determination of DNA based on the measurement of enhanced resonance light scattering.

A novel assay of DNA with a sensitivity at the nanogram level is proposed based on the measurement of enhanced resonance light scattering (RLS) signals resulting from the interaction of Janus Green B (JGB) with DNA. At pH 6.37 and ionic strength < 0.20, the RLS signals of JGB were greatly enhanced by DNA in the region of 300-650 nm characterized by three peaks at 416.0, 452.0 and 469.2 nm. The binding properties were examined using a Scatchard plot based on the measurement of the enhanced RLS data at 416.0 nm at a high JGB: DNA molar ratio (R > 2.22), and an aggregation mechanism of JGB in the presence of DNA at the nanogram level is proposed. Linear relationships can be established between the enhanced RLS intensity and DNA concentration in the range 0-3.5 micrograms ml-1 for both calf thymus DNA (ctDNA) and fish sperm DNA (fsDNA) if 2.0 x 10(-5) M JGB is employed. The limits of determination were 8.7 ng ml-1 for ctDNA and 9.9 ng ml-1 for fsDNA, respectively. Synthetic samples were analysed satisfactorily.

Azo Compounds↗
PubMed2000

Transforming growth factor-beta 1 in the developing mouse pancreas: a potential regulator of exocrine differentiation.

Transforming growth factor-beta 1 (TGF-beta 1) is known to regulate cell growth, differentiation, and function in developing mammalian systems. Altering TGF-beta 1 expression in the developing pancreas has been shown to affect both exocrine and endocrine development, suggesting that it is an important regulator of pancreatic organogenesis. We proposed to examine the ontogeny of TGF-beta 1 mRNA expression in the developing pancreas, as well as characterize the patterns of relative TGF-beta 1 gene expression and activity. We performed in situ hybridization for TGF-beta 1 on pancreas specimens obtained from CD-1 mice on gestational days 12.5 (E12.5), 15.5 (E15.5), and 18.5 (18.5). We also isolated mRNA from the pancreas on each of these days and performed a semi-quantitative reverse transcriptase polymerase chain reaction (RT-PCR) to assess relative TGF-beta 1 expression as a function of gestational age. Finally, we performed a TGF-beta 1 ELISA with media conditioned by embryonic pancreas from gestational days 15.5 and 18.5. By in situ hybridization, TGF-beta 1 mRNA is expressed exclusively in the E12.5 pancreatic epithelium, sparing the surrounding mesenchyme. As pancreatic organogenesis progresses, TGF-beta 1 mRNA expression localizes predominantly to the developing acini. TGF-beta 1 gene expression appears modest through E15.5 but is upregulated near the end of gestation, at E18.5. TGF-beta 1 activity, by ELISA, is also upregulated at E18.5. TGF-beta 1 may thus be a modulator of pancreatic organogenesis. Modest TGF-beta 1 expression through E15.5 may be permissive for exocrine lineage selection. TGF-beta 1 expression may then become critical for terminal acinar differentiation. Upregulated TGF-beta 1 expression at the end of gestation may be important for islet formation, and it may be necessary to inhibit continued proliferation and differentiation of pluripotent cells within the pancreatic ductal epithelium.

Animals↗
PubMed2000

Vasopressin V1a receptor antagonism does not reverse adrenocorticotrophin-induced hypertension in the rat.

1. The role of arginine vasopressin (AVP) was examined in adrenocorticotrophin (ACTH)-induced hypertension in Sprague-Dawley rats using the non-peptide AVP V1a receptor antagonist OPC 21268. 2. In an acute study, six rats were pretreated with ACTH for 11 days and direct arterial blood pressure (4 h), plasma osmolality and electrolyte concentrations were measured after OPC 21268 gavage. In a chronic study, 40 rats were randomly divided into four groups: (i) sham injection + sham gavage; (ii) ACTH + sham gavage; (iii) sham injection + OPC 21268; or (iv) ACTH + OPC-21268 for 16 days. Systolic blood pressure (SBP), water intake, urine volume (UV), urine osmolality and electrolytes, food intake, bodyweight and plasma osmolality and electrolyte concentrations were measured. 3. In the acute study, direct mean arterial blood pressure did not change with OPC 21268 (122+/-2 and 120+/-3 mmHg at 0 and 240 min, respectively). 4. In the chronic study, OPC 21268 did not affect ACTH-induced rises in blood pressure (from 125+/-2 (control) to 145+/-5 mmHg (group 4) compared with 122+/-3 (control) to 149+/-5 mmHg (group2)). Water intake and UV increased (from 29+/-2 to 83+/-6 mL/day; and from 5+/-1 to 36+/-5 mL/day, respectively) and the change in bodyweight decreased from 0+/-2 to -107+/-7 g. 5. These results suggest that AVP (at the V1a receptor) does not play a significant role in the maintenance of ACTH-induced hypertension.

Adrenocorticotropic Hormone↗
PubMed2000

Role of nitric oxide in adrenocorticotrophin-induced hypertension: L-arginine effects reversed by N-nitro-L-arginine.

1. L-arginine prevents adrenocorticotrophin (ACTH)-induced hypertension in the rat. To confirm that this effect is mediated through the nitric oxide (NO) system, we examined whether N-nitro-L-arginine (NOLA) could reverse the L-arginine-induced blockade of ACTH-induced hypertension. 2. Blood pressure and metabolic parameters were examined in sham-, ACTH-, L-arginine + sham-, NOLA + sham-, ACTH + L-arginine- and ACTH + L-arginine + NOLA-treated Sprague-Dawley rats (n = 40). 3. Adrenocorticotrophin treatment increased systolic blood pressure (SBP), water intake and urine output and decreased bodyweight. N-Nitro-L-arginine alone increased SBP without affecting metabolic variables. L-Arginine alone did not affect blood pressure. The SBP was lower in L-arginine + ACTH- than ACTH-treated rats (P < 0.001), but was higher following ACTH + L-arginine + NOLA than ACTH + L-arginine (P < 0.05). 4. N-Nitro-L-arginine reversed the blood pressure-lowering effect of L-arginine in ACTH-induced hypertension in the rat, supporting the notion that NO plays a role in the hypertension.

Adrenocorticotropic Hormone↗
PubMed2000

Acidic motif responsible for plasma membrane association of the voltage-dependent calcium channel beta1b subunit.

Voltage-dependent calcium channels consist of a pore-forming transmembrane alpha1-subunit, which is known to associate with a number of accessory subunits, including alpha2-delta- and beta-subunits. The beta-subunits, of which four have been identified (beta1-4), are intracellular proteins that have marked effects on calcium channel trafficking and function. In a previous study, we observed that the beta1b-subunit showed selective plasma membrane association when expressed alone in COS7 cells, whereas beta3 and beta4 did not. In this study, we have examined the basis for this, and have identified, by making chimeric beta-subunits, that the C-terminal region, which shows most diversity between beta-subunits, of beta1b is responsible for its plasma membrane association. Furthermore we have identified, by deletion mutations, an 11-amino acid motif present in the C terminus of beta1b but not in beta3 (amino acids 547-556 of beta1b, WEEEEDYEEE), which when deleted, reduces membrane association of beta1b. Future research aims to identify what is binding to this sequence in beta1b to promote membrane association of this calcium channel subunit. It is possible that such membrane association is important for the selective localization or clustering of particular calcium channels with which beta1b is associated.

Animals↗
PubMed2000

Thyrotropin-releasing hormone and its receptor in the cerebellum of inferior olive destroyed rat brain.

To study the pathophysiology of olivopontocerebellar atrophy (OPCA), we destroyed inferior olive nuclei of male Wistar rats using 3-acetyl pyridine (3-AP) + harmaline + niacinamide. These rats showed a sluggish and ataxic gait. To elucidate the relationship between thyrotropin releasing hormone (TRH) in the Purkinje cell of cerebellum and the inferior olive nucleus, we investigated the concentrations of TRH in the cerebellar cortex, nuclei, and medulla oblongata including the inferior olive nuclei using radioimmunoassay method as well as TRH receptor in the Purkinje cells of cerebellum using immunohistochemical method. All statistical comparisons were done using non-parametric tests (Mann-Whitney U-test). We found that two weeks after the treatment, TRH concentrations in the cerebellar cortex as well as nuclei were significantly lower than in the controls but no significant difference in the medulla oblongata was observed between 3-AP treated rats and controls. Moreover, four weeks after the treatment, TRH-receptor positive Purkinje cell counts were significantly fewer than in the controls. These results suggest that TRH in the Purkinje cell of cerebellum may play a role in the ataxic gait observed in the rats whose inferior olive were destroyed.

Animals↗
PubMed2000

L-arginine partially reverses established adrenocorticotrophin-induced hypertension and nitric oxide deficiency in the rat.

BACKGROUND: L-arginine treatment prevents adrenocorticotrophin (ACTH) induced hypertension in the rat. This study examined whether L-arginine treatment could reverse established ACTH hypertension and its effects on markers of decreased NO activity. METHODS: Sixty-four male Sprague-Dawley rats were randomly divided into 6 groups given 12 days of treatment: (1) sham (0.9% NaCl, 0.5 ml/kg, subcutaneously, sc, n = 16); (2) ACTH (0.5 mg/kg/day, sc, n = 16); (3) sham + L-arginine (0.6% in food, from treatment day 8 onwards, n = 10); (4) ACTH + L-arginine (n = 10); (5) sham + D-arginine (0.6% in food, from T 8 onwards) (n = 6); and (6) ACTH + D-arginine (n = 6). Systolic blood pressure, water intake, urine volume, and body weight were measured every second day. At the end of the experiments, plasma and urinary nitrate/nitrite (NOx), plasma amino acid concentrations (in groups 1-4), and urinary cyclic guanosine monophosphate (cGMP) concentrations were measured. RESULTS: Sham, sham + L-arginine, and sham + D-arginine treatments did not affect blood pressure. ACTH increased systolic blood pressure (from 121 +/- 1 to 147 +/- 2 mmHg, p < 0.001, pooled control vs treatment day 12, mean +/- sem), and this was partially reversed by L-arginine (group 4: from 141 +/- 2 on day 8 to 133 +/- 1 mmHg on day 12, n = 10, p < 0.001). In contrast, D-arginine did not affect blood pressure in ACTH-treated rats (group 6). ACTH increased water intake and urine volume and decreased body weight, and L-arginine administration did not alter these parameters. ACTH decreased plasma citrulline (group 1 vs 2: 115 +/- 7 vs 67 +/- 6 micro M/L, n = 16, p < 0.001) and NOx concentrations (group 1 vs 2: 8.3 +/- 0.8 vs 4.5 +/- 0.6 microM/L, n= 10, p < 0.001) and these decreases were reversed by L-arginine treatment (group 4: citrulline 98 +/- 9 micro M/L, NOx 9.1 +/- 1.6 micro M/L, group 2 vs 4, both p < 0.05). ACTH produced marked increases in urinary cGMP excretion (group 1 vs 2: 0.5 +/- 0.1 vs 1.9 +/- 0.4 nmol/24 h, p < 0.01). CONCLUSION: Supplementation with L-arginine partly reversed established ACTH-induced hypertension and restored plasma NOx and citrulline concentrations to levels seen in sham-treated rats. These data are consistent with previous studies suggesting that functional NO deficiency has a role in ACTH-induced hypertension in rats.

Adrenocorticotropic Hormone↗
PubMed2000

Tanshinone II-A inhibits low density lipoprotein oxidation in vitro.

Tanshinone II-A (TSII-A) is a major component of Salvia miltorrhiza Bunge which has long been used for preventing and ameliorating anginal pain in China. However the effect of TSII-A on low density lipoprotein (LDL) oxidation has not been studied. The present study was performed to investigate the effects of TSII-A on LDL oxidation using four oxidizing systems, including copper-, peroxyl radical- and peroxynitrite-initiated and macrophage-mediated LDL oxidation. LDL oxidation was measured in terms of formation of thiobarbituric acid-reactive substances (TBARS), relative electrophoretic mobility (REM) on agarose gel and lag time. In all four systems, TSII-A has apparent antioxidative effects against LDL oxidation, as evidenced by its dose-dependent inhibition of TBARS formation, prolongation of lag time and suppression of increased REM. Regarding the mechanism underlying its antioxidative effect, TSII-A neither scavenged superoxide nor peroxynitrite. It also did not chelate copper. But it has mild peroxyl radical scavenging activity. The direct binding to LDL particles and conformational change of LDL structure by TSII-A were suggested, because it increased negative charge of LDL which was shown by increased REM on agarose gel. In conclusion, TSII-A is an effective antioxidant against LDL oxidation in vitro. The underlying mechanism appears to be related to its peroxyl radical scavenging and LDL binding activity.

Abietanes↗
PubMed2000

An intermediate state of the gamma-aminobutyric acid transporter GAT1 revealed by simultaneous voltage clamp and fluorescence.

The rat gamma-aminobutyric acid transporter GAT1 expressed in Xenopus oocytes was labeled at Cys74, and at one or more other sites, by tetramethylrhodamine-5-maleimide, without significantly altering GAT1 function. Voltage-jump relaxation analysis showed that fluorescence increased slightly and monotonically with hyperpolarization; the fluorescence at -140 mV was approximately 0. 8% greater than at +60 mV. The time course of the fluorescence relaxations was mostly described by a single exponential with voltage-dependent but history-independent time constants ranging from approximately 20 ms at +60 mV to approximately 150 ms at -140 mV. The fluorescence did not saturate at the most negative potentials tested, and the midpoint of the fluorescence-voltage relation was at least 50 mV more negative than the midpoint of the charge-voltage relation previously identified with Na(+) binding to GAT1. The presence of gamma-aminobutyric acid did not noticeably affect the fluorescence waveforms. The fluorescence signal depended on Na(+) concentration with a Hill coefficient approaching 2. Increasing Cl(-) concentration modestly increased and accelerated the fluorescence relaxations for hyperpolarizing jumps. The fluorescence change was blocked by the GAT1 inhibitor, NO-711. For the W68L mutant of GAT1, the fluorescence relaxations occurred only during jumps to high positive potentials, in agreement with previous suggestions that this mutant is trapped in one conformational state except at these potentials. These observations suggest that the fluorescence signals monitor a novel state of GAT1, intermediate between the E*(out) and E(out) states of Hilgemann, D.W., and C.-C. Lu (1999. J. Gen. Physiol. 114:459-476). Therefore, the study provides verification that conformational changes occur during GAT1 function.

Animals↗
PubMed2000

Fibrodysplasia ossificans progressiva, a heritable disorder of severe heterotopic ossification, maps to human chromosome 4q27-31.

Fibrodysplasia ossificans progressiva (FOP) is a severely disabling, autosomal-dominant disorder of connective tissue and is characterized by postnatal progressive heterotopic ossification of muscle, tendon, ligament, and fascia and by congenital malformation of the great toes. To identify the chromosomal location of the FOP gene, we conducted a genomewide linkage analysis, using four affected families with a total of 14 informative meioses. Male-to-male transmission of the FOP phenotype excluded X-linked inheritance. Highly polymorphic microsatellite markers covering all human autosomes were amplified by use of PCR. The FOP phenotype is linked to markers located in the 4q27-31 region (LOD score 3.10 at recombination fraction 0). Crossover events localize the putative FOP gene within a 36-cM interval bordered proximally by D4S1625 and distally by D4S2417. This interval contains at least one gene involved in the bone morphogenetic protein-signaling pathway.

Chromosome Mapping↗
PubMed2000

Antibodies to the major linear neutralizing domains of cytomegalovirus glycoprotein B among natural seropositives and CMV subunit vaccine recipients.

The gB protein (gpUL55) of human cytomegalovirus (CMV) contains C-terminal (AD-1) and N-terminal (AD-2) linear immunodominant neutralizing domains. To measure antibodies to these epitopes, a modified protein (delta-gB) lacking heavily glycosylated intervening regions, the transmembrane domain, and the cytoplasmic domain, was expressed in recombinant baculovirus-infected cells. Eighty-six percent of 600 naturally CMV-seropositive individuals and 93% of 121 gB vaccine recipients had antibodies to delta-gB as detected by enzyme-linked immunosorbent assay (ELISA). The antibody level in vaccinees (median optical density [OD] = 1.73) exceeded that in natural seropositives (median OD = 0.94; p < .0001). Eleven percent of 95 natural seropositives and 7% of 120 gB vaccinees lacked A-gB antibodies but had neutralizing activity. Among subjects with delta-gB antibody, there were weak correlations between antibody level and neutralizing titer. These data suggest that antibodies to linear neutralizing gB domains are highly prevalent in naturally-infected individuals and regularly develop in gB vaccinees. However, for some individuals, discontinuous and/or linear epitopes not represented on delta-gB may be more important in the generation of neutralizing responses.

Adult↗
PubMed2000

Adrenal oncocytic pheochromocytoma.

We report a case of adrenal oncoctyic pheochromocytoma in a 37-year-old woman. The patient presented with a 2-year history of an increase in abdominal girth. Computed tomographic studies revealed a large left adrenal mass, which was subsequently excised. Grossly, the tumor measured 17 x 14 x 8.5 cm, weighed 1,150 g, and had a solid, brown cut surface. Histologically, it consisted of large polygonal tumor cells containing eosinophilic granular cytoplasm and arranged in nesting, alveolar, and trabecular patterns. Electron microscopy revealed closely packed mitochondria and dense-core membrane-bound granules in almost all tumor cells. The latter were immunohistochemically positive for chromogranin, synaptophysin, neuron-specific enolase, neurofilament, serotonin, bombesin, ACTH, vimentin, desmin, S-100 protein, and cytokeratins, including AE1/3, CAM 5.2, cytokeratin 7, and cytokeratin 20. To the best of our knowledge, this is the first reported case of adrenal oncocytic pheochromocytoma confirmed by ultrastructural study. The immunoreactivity of this tumor adds several unusual features to the wide immunohistochemical spectrum of pheochromocytoma.

Adenoma, Oxyphilic↗
PubMed2000

Phase behavior and blue-phase-III-isotropic critical point in (R)-(S) mixtures of a chiral liquid crystal with a direct twist-grain-boundary to blue-phase transition

We have investigated mixtures of the (R) and (S) enantiomers of a chiral liquid crystal, (R)- or (S)-1-methylheptyl 3'-fluoro-4'-(3-fluoro-4-octadecyloxybenzoyloxy)tolane-4-carboxylate using high-resolution adiabatic scanning calorimetry. The pure (R) compound has a direct transition from the twist-grain-boundary to the blue phase without an intermediary chiral nematic phase. For the blue phases a different kind of phase behavior as a function of enantiomeric excess is observed, most probably related to the presence of a twist-grain-boundary-A instead of a chiral nematic phase below the blue phases. The general form of this phase diagram is compared with traditional blue-phase behavior. Furthermore a blue-phase-III-isotropic phase critical point, analoguous to that of a liquid-gas system, is observed, consistent with experimental and theoretical work recently published in this field. Finally, the effect of changing enantiomeric excess on the latent heats of the different first order phase transitions is measured and discussed.

Journal Article↗
PubMed2000

Short-time dynamics of an ising system on fractal structures

The short-time critical relaxation of an Ising model on a Sierpinski carpet is investigated using Monte Carlo simulation. We find that when the system is quenched from high temperature to the critical temperature, the evolution of the order parameter and its persistence probability, the susceptibility, and the autocorrelation function all show power-law scaling behavior at the short-time regime. The results suggest that the spatial heterogeneity and the fractal nature of the underlying structure do not influence the scaling behavior of the short-time critical dynamics. The critical temperature, dynamic exponent z, and other equilibrium critical exponents beta and nu of the fractal spin system are determined accurately using conventional Monte Carlo simulation algorithms. The mechanism for short-time dynamic scaling is discussed.

Journal Article↗