PubMed Health⌕ Search

SEARCH · PubMed Health

Results for “variable methylation”

Explore indexed PubMed citations for clinical trials, systematic reviews and public health research. Read source abstracts and follow each citation to its original PubMed record.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 361 records · Page 20Linked to original sources
PubMed2001

X-ray structure of bovine pancreatic phospholipase A2 at atomic resolution.

Using synchrotron radiation and a CCD camera, X-ray data have been collected from wild-type bovine pancreatic phospholipase A(2) at 100 K to 0.97 A resolution allowing full anisotropic refinement. The final model has a conventional R factor of 9.44% for all reflections, with a mean standard uncertainty for the positional parameters of 0.031 A as calculated from inversion of the full positional least-squares matrix. At 0.97 A resolution, bovine pancreatic phospholipase A(2) reveals for the first time that its rigid scaffolding does not preclude flexibility, which probably plays an important role in the catalytic process. Functionally important regions (the interfacial binding site and calcium-binding loop) are located at the molecular surface, where conformational variability is more pronounced. A cluster of 2-methyl-2,4-pentanediol molecules is present at the entrance of the hydrophobic channel that leads to the catalytic site and mimics the fatty-acid chains of a substrate analogue. Bovine pancreatic phospholipase A(2) at atomic resolution is compared with previous crystallographic structures and with models derived from nuclear magnetic resonance studies. Given the high structural similarity among extracellular phospholipases A(2) observed so far at lower resolution, the results arising from this structural analysis are expected to be of general validity for this class of enzymes.

Animals↗
PubMed1988

Characterization of Vibrio metschnikovii and Vibrio gazogenes by DNA-DNA hybridization and phenotype.

Vibrio metschnikovii and Vibrio gazogenes are two new Vibrio species that have been little studied. Thirteen strains of V. metschnikovii were highly related to the type strain, NCTC 8443, by DNA-DNA hybridization. Relatedness values were 83 to 90% at 60 degrees C and 75 to 84% at the more stringent 75 degrees C. Divergence values ranged from 0.7 to 1.9. Strains of V. metschnikovii were oxidase negative and did not reduce nitrate to nitrite. The other phenotypic characteristics agreed with published data. Twenty-three strains of V. gazogenes were isolated from salt marshes and marshy areas on the coast of North and South Carolina. A new medium, marine agar supplemented with an additional 2.5% agar, reduced the problem of swarming by marine Vibrio species and enhanced the isolation of V. gazogenes and other organisms. By DNA-DNA hybridization, 22 of 23 strains were 76% or more related to the type strain of V. gazogenes, ATCC 29988. However, four DNA hybridization subgroups were defined on the basis of divergence values and/or phenotype. Strains of DNA group 1 were more highly related to each other, and this group contained the type strain and six other strains. Strains of DNA group 2 were more highly related to each other, and this group contained reference strain ATCC 43942 and 14 other strains. Strains of DNA group 1 did not ferment melibiose or D-sorbitol (one strain was sorbitol positive), but strains of DNA group 2 fermented both sugars. A revised phenotypic description of V. gazogenes based on 24 strains was written on the basis of reactions (within 2 days of incubation) at 25 degrees C in media supplemented with Na+, K+, and Mg2+. Positive results (100% positive unless indicated) included motility; gas production during fermentation (96% at 2 days, 100% at 3 to 7 days); growth in nutrient broth with the addition of 1% NaCl (88%), 2% NaCl, 3.5% NaCl, 6% NaCl, 8% NaCl, and 10% NaCl (92%); dry red or orange colonies on marine agar; and fermentation of L-arabinose, cellobiose, D-galactose (88%), D-glucose, lactose (88%), maltose, D-mannitol (96%), D-mannose, salicin, sucrose, trehalose, and D-xylose. Negative results included oxidase; nitrate reduction to nitrite (4% positive); indole production; lysine decarboxylase; ornithine decarboxylase; arginine dihydrolase; swarming; growth on TCBS agar; growth in nutrient broth with 0% NaCl, 0.1% NaCl, 0.2% NaCl, 0.3% NaCl, and 0.4% NaCl (8% positive); and fermentation of adonitol, D-arabitol, dulcitol, erythritol, D-galacturonate, i-inositol, alpha-methyl-D-glucoside, raffinose, and L-rhamnose. Variable results were found for the Voges-Proskauer reaction (62% positive), growth in nutrient broth plus 0.5% NaCl (29%) and 12% NaCL (42%), and fermentation of melibiose (71%) and D-sorbitol (71%).

DNA, Bacterial↗
PubMed2003

Retinogeniculate synaptic properties controlling spike number and timing in relay neurons.

Retinal ganglion cells (RGC) transmit visual signals to thalamocortical relay neurons in the lateral geniculate nucleus via retinogeniculate synapses. Relay neuron spike patterns do not simply reflect those of RGCs, but the mechanisms controlling this transformation are not well understood. We therefore examined synaptic properties controlling the strength and precision of relay neuron firing in mouse (p28-33) brain slices using physiological stimulation patterns and a combination of current clamp and dynamic clamp. In tonic mode (-55 mV), activation of single RGC inputs elicited stereotyped responses in a given neuron. In contrast, responses in different neurons varied from unreliable, to faithfully following, to a gain in the number of spikes. Dynamic clamp experiments indicated these different responses primarily reflected variability in the amplitudes of the N-methyl-d-aspartate (NMDA) and AMPA components. Each of these components played a distinct role in transmission. The AMPA component evoked a single precisely timed, short-latency spike per stimulus, but efficacy decreased during repetitive stimulation due to desensitization and depression. The NMDA component elicited longer-latency spikes and multiple spikes per stimulus and became more effective during repetitive stimuli that led to NMDA current summation. We found that in burst mode (-75 mV), where low-threshold calcium spikes are activated, AMPA and NMDA components and synaptic plasticity influenced spike number, but no combination enabled relay cells to faithfully follow the stimulus. Thus the characteristics of AMPA and NMDA currents, the ratio of these currents and use-dependent plasticity interact to shape how RGC activity is conveyed to relay neurons.

Action Potentials↗
PubMed2000

Cloning and functional expression of the hNPY Y5 receptor in human endometrial cancer (HEC-1B) cells.

Aiming to develop a functional assay for the human NPY Y5 receptor based on adenylyl cyclase activity, HEC-1B cells, in which cAMP synthesis can be efficiently stimulated with forskolin, were selected for the transfection with the pcDNA3-Y5-FLAG and the pcDEF3-Y5 vectors. After optimization of the transfection procedure, the binding of [3H]propionyl-NPY to transiently and stably expressed Y5 receptors was determined. The affinities of NPY, NPY derivatives, and rPP (pNPY > or = p(Leu31Pro34)NPY = p(2-36)NPY > or = p(D-Trp32)NPY > p(13-36)NPY > rPP) were in accordance with the NPY Y5 receptor subtype. For [3H]propionyl-pNPY approximately 1.7 x 10(5) and 1 x 10(6) binding sites per transiently and stably transfected cell, respectively, were determined. The KD values were 2.4 +/- 0.4 and 1.7 +/-0.2 nM, respectively. Due to the high expression of the receptor protein, both stably and transiently transfected cells can be conveniently used in routine radioligand binding studies. By contrast, functional assays were only feasible with HEC-1B cells stably expressing the Y5 receptor. In these cells, 10 nM pNPY inhibited the forskolin-stimulated cAMP synthesis by 75%. This effect was partially antagonized by the Y5 antagonist N-¿trans-[4-(2-naphthylmethylamino)-methyl]cyclohexylmethyl) naphthalene-2-sulfonamide. Although the genetic variability of cancer cells is in principle incompatible with a stable phenotype, both ligand binding characteristics and functionality of the Y5 receptor remained unchanged for more than 30 passages.

Cloning, Molecular↗
PubMed1995

[Fragile X syndrome: clinical and molecular genetics correlations].

The fragile X form of mental retardation is presently recognized as the most frequent hereditable cause of mental impairment. The estimated frequency among males is 1 in 1250, and 1 in 2000 among females. Beside mental impairment and behavioural disturbance with hyperactivity and autistic features, the patients are characterized by morphological anomalies, such as an oblong face, broad, rectangular chin, large protruding ears and macro-orchidism. A less severe clinical expression can be found among females heterozygotes of the disorder, manifesting mainly as learning disability. The disorder is associated with the expression of a fragile site at Xq27.3 under conditions of folate depletion in the chromosome culture medium. The molecular mechanism is based on the expansion of a trinucleotide repeat [CCG]n in the promoter region of the FMR1 gene resulting in methylation of the gene. The trinucleotide repeat shows variable lengths of 6 to 53 repeats in the general population, 60 to 200 repeats in carriers of a premutation and over 200 repeats in patients with fragile X syndrome.

Adult↗
PubMed1996

Reactivity of purified complement component 3b with bovine neutrophils and modulation of complement receptor 1.

OBJECTIVE: To study binding of purified complement component C3b to bovine blood and mammary neutrophils (PMN) after various treatments and determine their ability to modulate receptor numbers. DESIGN: Cell isolation, activation, and flow cytometric studies. ANIMALS: Healthy lactating Holstein cattle. PROCEDURE: Complement component C3b (18,300 kd) was isolated from bovine serum by column chromatography, and flow cytometric assays using fluorescein isothiocyanate-labeled C3b were developed to evaluate binding to PMN complement receptor 1. Multiple substances were tested to determine their overall effect on C3b binding to PMN. Blood and milk PMN were isolated by differential centrifugation and exposed to optimal concentrations of recombinant human C5a, formyl-methyl leucyl phenylalanine, recombinant bovine interferon-gamma, variable concentrations of phorbol myristate acetate (0.01 to 100 ng), calcium ionophore A23187, serum-opsonized zymosan, zymosan-activated serum (ZAS), zymosan-activated plasma (ZAP), and hydrocortisone acetate (25 and 70 ng). Additionally, mammary and blood PMN were preincubated in skim milk and whey. RESULTS: Variable concentrations of phorbol myristate acetate caused a dose-dependent increase in percentage of PMN binding C3b, and increased the amount of C3b bound per cell. Significant increases were observed after PMN treatment with calcium ionophore, serum opsonized zymosan, ZAS, and ZAP; conversely, incubation of PMN with hydrocortisone acetate resulted in reduced overall binding of C3b. Mammary PMN consistently bound more C3b, which was attributed to their activation during migration into the mammary gland. Binding of C3b was inhibited by skim milk. Activation of blood PMN with PMA, ZAS, and ZAP elicited larger responses than those observed for mammary PMN. CONCLUSIONS: Modulation of complement receptors on bovine PMN is possible. Additionally, significant difference between the level of binding of C3b to blood and milk PMN, with milk PMN having higher binding, may be attributable to migration of PMN into the mammary gland, causing increased receptor expression. CLINICAL RELEVANCE: Contribution to a greater understanding of the role of complement in bovine immunologic systems, leading to testing for in vivo enhancement of bovine immune responses to invading pathogens.

Animals↗
PubMed1996

Superficial versus deep: options in venous drainage of the radial forearm free flap.

We performed a fresh cadaver dissection study of the superficial venous system (cephalic vein and its branches) and the deep venous system (venae comitantes) of the radial forearm to assess the suitability of each system for venous anastomosis during free tissue transfer. We used methyl methacrylate to evaluate vessel diameters and anatomic variability of both venous systems. Colored radiopaque injectate allowed us to combine anatomic dissection with tissue radiographs. We discovered the cephalic vein to invariably be of larger caliber than the venae comitantes. Ensuring capture of the cephalic vein in the flap necessitated additional dorsoradial subcutaneous dissection beyond the boundaries of the skin flap in four of ten specimens. The vessel diameters of the venae comitantes in four cadavers were less than 2 mm. Proximal confluence of the two venae comitantes, and communication between the deep and superficial venous systems were encountered in only four cases. In these cases, had an anastomotic site been chosen proximal to such a communication to ensure greater vessel caliber, pedicle length probably would have made free tissue transfer unwieldy. We recommend mapping the course of the cephalic vein before flap elevation and maintaining a wide proximal subcutaneous pedicle to capture the best possible superficial drainage system. If the superficial venous system has been damaged (as by previous intravenous catheterization), one may not necessarily be able to rely on the vessel caliber of the deep venae comitantes for microvenous anastomosis.

Brachial Artery↗
PubMed2006

Opioid-binding protein/cell adhesion molecule-like (OPCML) gene and promoter methylation status in women with ovarian cancer.

OBJECTIVE: The expression profile of the OPMCL gene was studied to find out if there was any evidence of a CpG island methylator phenotype and if there was an association of CpG island methylation with the gene downregulation in women with ovarian cancer. MATERIAL AND METHODS: Expression of OPCML in 43 ovarian cancer tumor samples and in 4 normal ovaries was determined by RT-PCR. Methylation status of OPCML promoter region was studied with methylation-specific PCR (MSP) method. Possible associations with selected clinicopathologic variables: FIGO stage, histological grade, patient's age and menopausal status were tested. RESULTS: In all normal ovarian samples OPCML mRNA was present, but it was not detectable in 24 of 43 ovarian cancer cases. We have not found the relationship between age and menopausal status with the presence of RTPCR product of OPCML. Hypermethylation of OPCML was not correlated to FIGO stage, however, in 80% of cases with methylated OPCML early clinical stage was also present. Tumor grading and histological type had no significant influence on the presence of hypermethylation of OPCML gene. In 20 of 43 cases of ovarian cancer methylated product of MSP amplification was present. In a group of OPCMLmRNA-negative tumors there were 75% of cases with hypermethylated exon of OPCML and the correlation between these variables was statistically significant (chi2 =17.7; p=0,00003). No promoter hypermethylation of the studied gene was found in normal ovaries. CONCLUSIONS: Reduced OPCMPL gene expression in ovarian cancer in comparison to normal ovaries could be related to the hypermethylation of promoter region. This epigenetic alteration may be the reason of gene silencing and the loss of suppressor function.

Adult↗
PubMed1989

Multifactorial hamster respiratory carcinogenesis with interdependent effects of cannula-induced mucosal wounding, saline, ferric oxide, benzo[a]pyrene and N-methyl-N-nitrosourea.

The carcinogenic response induced in the respiratory tract of Syrian golden hamsters by repeated intratracheal instillations of benzo[a]pyrene (BP) adsorbed to ferric oxide (Fe2O3) particles suspended in saline, is shown to result from the interactions of these factors and cannula-induced tracheal wounding. Previous acute studies of intratracheal cannulation (ITC) versus intralaryngeal cannulation (ILC) showed that tracheal cell proliferation increased significantly in ITC-induced mucosal wounds. Only mild increases in intrapulmonary cell proliferation were produced by Fe2O3-saline given by ILC or ITC (Keenan et al., Cancer Res., 49: 1521-1527, 1989). The present chronic studies included the following variables: a single instillation by ILC of N-methyl-N-nitrosourea (MNU) at 5 weeks of age; 15 weekly treatments (beginning at 7 weeks of age) by ILC or ITC alone, or with instillations of saline, or Fe2O3-saline, or BP-Fe2O3-saline; and appropriate controls. Repeated ITC-induced tracheal wounds caused persistent tracheal epithelial hyperplasia, metaplasia and/or atrophy and submucosal fibroplasia during the observation period of 22 to 78 weeks of age (the time of terminal sacrifice). Tracheal cancers (in situ or invasive carcinomas) were seen only in those hamsters which had received repeated ITC and one or both carcinogens. The cancer latency was shortest and the incidence of tracheal (50%) and main-stem bronchial (21%) cancers highest in hamsters given MNU and repeated ITC with BP-Fe2O3-saline. Hamsters given carcinogens by ILC (which induced laryngeal but not tracheal wounds) developed proliferative lesions and cancers of the larynx but no tracheobronchial cancers. These data show the singular importance of repeated ITC-induced intratracheal wounding as an enhancing factor in this respiratory carcinogenesis model. The findings suggest that the mechanism of tumor enhancement involves not only changes in target epithelial cell proliferation, but also alterations in normal epithelial-mesenchymal interactions during tracheal regeneration from repeated chronic submucosal inflammation and mesenchymal repair. In the present experimental model, a single dose of MNU at 5 weeks of age, repeated instilled doses of BP, and tracheal mucosal wounding were each found to be important determinants of the carcinogenic response. Additional effects were observed for instilled Fe2O3 particles, and possibly saline. Interplay of all these factors, as well as of genetic, nutritional, and infectious factors, are considered in relation to risk assessment and prevention.

Animals↗
PubMed1995

CpG methylation represses the activity of the rat prolactin promoter in rat GH3 pituitary cell lines.

In the present report, we have investigated the role of DNA methylation on the binding and trans-acting properties of transcription factors involved in the regulation of the rat prolactin (rPRL) gene, specifically Pit-1. To this aim we took advantage of a model system composed of three GH3 rat pituitary tumor cell lines that greatly differed in the extent of rPRL gene methylation and in the level of rPRL gene expression. Northern blot analyses indicated that identical species of Pit-1 mRNA were present to similar extent in the three GH3 cell lines. Electrophoretic mobility shift assays further demonstrated that Pit-1 was present in nuclear extracts and displayed equal affinities to bind the 1P responsive element encompassing the -65 to -38 region of the rPRL promoter, whatever the GH3 cell line tested. These data suggested that differential expression of the rPRL gene among cell lines did not result from variable amounts of Pit-1. By combining in vitro methylation and transient transfection experiments with a rPRL promoter-driven CAT construct, we showed that extensive methylation at CpG sites abolished the expression of the reporter gene. Furthermore, in vivo competition assays demonstrated that CpG methylation inhibited gene expression by preventing the binding of transcription factors We propose that related mechanisms linked to DNA methylation might alter the activity of the endogenous PRL gene in the low expressing cell line.

Animals↗
PubMed1996

Variability in biological exposure indices using physiologically based pharmacokinetic modeling and Monte Carlo simulation.

By using physiologically based pharmacokinetic (PBPK) modeling coupled with Monte Carlo simulation, the interindividual variability in the concentrations of chemicals in a worker's exhaled breath and urine were estimated and compared with existing biological exposure indices (BEIs). The PBPK model simulated an exposure regimen similar to a typical workday, while exposure concentrations were set to equal the ambient threshold limit values (TLVs) of six industrial solvents (benzene, chloroform, carbon tetrachloride, methylene chloride, methyl chloroform, and trichloroethylene). Based on model predictions incorporating interindividual variability, the percentage of population protected was derived using TLVs as the basis for worker protection. Results showed that current BEIs may not protect the majority or all of the workers in an occupational setting. For instance, current end-expired air indices for benzene and methyl chloroform protect 95% and less than 10% of the worker population, respectively. Urinary metabolite concentrations for benzene, methyl chloroform, and trichloroethylene were also estimated. The current BEI recommendation for phenol metabolite concentration at the end-of-shift sampling interval was estimated to protect 68% of the worker population, while trichloroacetic acid (TCAA) and trichloroethanol (TCOH) concentrations for methyl chloroform exposure were estimated to protect 54% and 97%, respectively. The recommended concentration of TCAA in urine as a determinant of trichloroethylene exposure protects an estimated 84% of the workers. Although many of the existing BEIs considered appear to protect a majority of the worker population, an inconsistent proportion of the population is protected. The information presented in this study may provide a new approach for administrative decisions establishing BEIs and allow uniform application of biological monitoring among different chemicals.

Humans↗
PubMed1978

Metabolism of 3, 4-dihydroxyphenylalanine, its metabolites and analogues in vivo in the rat: urinary excretion pattern.

The metabolism and interrelationships of orally and intraperitoneally administered L-dopa, related amino acids and their metabolites have been studied 2. Amino acids were decarboxylated. N-Methyldopa formed dopamine but not epinine. D-Dopa was absorbed from the intestine and metabolized by a series of reactions which resulted in greater decarboxylation than was observed after L-dopa. Transamination was a minor pathway. 3. m-Hydroxylated phenylpyruvic acids were poorly reduced, but vanilpyruvic acid was reduced fairly readily. Lactic acids were largely unchanged. Lactic and pyruvic acids formed phenylethylamines and their metabolites. Small amounts of phenylpyruvic acids may be decarboxylated to phenylacetic acids. 4. Glycine conjugates were formed from phenylacetic acids, a partially reversible change 3,4-Dihydroxyphenylacetic acid was metabolized to homovanillic and m-hydroxyphenylacetic acids, especially when given orally. Little 3-hydroxy-4-methoxyphenylacetic acid was oxidized to 3,4-dihydroxyphenylacetic acid but some increase in m-hydroxyphenylacetic acid excretion was observed. 5. 2-Phenylethanol analogues were largely converted to the corresponding acids. 3,4-Dihydroxyphenylethanol was partially m-O-methylated before oxidation. 6. beta-Phenylethylamine analogues were oxidized mainly to phenylacetic acids. but a variable amount of analogous phenylethanol was also formed, especially from m-tyramine. Dopamine was O-methylated, a process not readily reversible. It was also p-dehydroxylated following oral and intraperitoneal administration but not after oral neomycin; biliary excretion of amines may be involved in this sequence of events. N-Methylated amines were oxidized less readily than the parent amine. 7. Differences in route of administration resulted in quantitative changes in degradation pathways, an effect deriving, to some extent, from p-dehydroxylation and O-methylation in the gut.

Alcohols↗
PubMed2003

The effect of dietary folate on genomic and p53-specific DNA methylation in rat colon.

Folate is an important mediator in the transfer of methyl groups for DNA methylation, abnormalities of which are considered to play an important mechanistic role in colorectal carcinogenesis. This study investigated the time-dependent effects of dietary folate on genomic and p53 (in the promoter region and exons 6-7) DNA methylation in rat colon, and how these changes are related to steady-state levels of p53 transcript. Despite a marked reduction in plasma and colonic folate concentrations, a large increase in plasma homocysteine (an accurate inverse indicator of folate status), and a progressive decrease in colonic S-adenosylmethionine (SAM; the primary methyl donor for methylations) to S-adenosylhomocysteine (SAH; a potent inhibitor of methylations) ratio, isolated folate deficiency did not induce significant genomic DNA hypomethylation in the colon. Paradoxically, isolated folate deficiency increased the extent of genomic DNA methylation in the colon at an intermediate time point (P = 0.022). Folate supplementation did not modulate colonic SAM, SAH and SAM to SAH ratios, and genomic DNA methylation at any time point. The extent of p53 methylation in the promoter and exons 6-7 was variable over time at each of the CpG sites examined, and no associations with time or dietary folate were observed at any CpG site except for site 1 in exons 6-7 at week 5. Dietary folate deprivation progressively decreased, whereas supplementation increased, steady-state levels of p53 transcript over 5 weeks (P < 0.05). Steady-state levels of p53 mRNA correlated directly with plasma and colonic folate concentrations (P = 0.41-0.49, P < 0.002) and inversely with plasma homocysteine and colonic SAH levels (r = -0.37-0.49, P < 0.006), but did not significantly correlates with either genomic or p53 methylation within the promoter region and exons 6-7. The data indicate that isolated folate deficiency, which significantly reduces steady-state levels of colonic p53 mRNA, is not associated with a significant degree of genomic or p53 DNA hypomethylation in rat colon. This implies that neither genomic or p53 hypomethylation within exons 6-7 nor aberrant p53 methylation within the promoter region is likely a mechanism by which folate deficiency enhances colorectal carcinogenesis in the rat.

Animals↗
PubMed1989

Effects of phencyclidine and other N-methyl-D-aspartate antagonists on the schedule-controlled behavior of rats.

The behavioral effects of phencyclidine (PCP) were compared with those of several compounds known to antagonize the actions of N-methyl-D-aspartate using two patterns of schedule-controlled responding in rats. Rates of variable interval responding suppressed by punishment were increased greatly by the benzodiazepine chlorodiazepoxide and showed small increases after MK-801 [(+)-5-methyl-10,11-dihydro-5H-dibenzo[a,d]cyclohepten-5,10-imine] . However, no consistent increases in response rates were produced by PCP, by the stereoisomers of N-allylnormetazocine (NANM: SKF 10,047) or by the anti-ischemic drug, ifenprodil. Small doses of PCP did increase rates of unpublished variable interval responding, as did a low dose of MK-801. Timing behavior maintained by a differential reinforcement of low rate schedule was disrupted by all the compounds studied. Response rates were increased by at least one dose of PCP, MK-801, (+)-NANM and 3-(2-carboxypiperazine-4-yl)propyl-1-phosphonic acid. The effect of MK-801, however, was considerably greater than that of the other compounds. Ifenprodil and (-)-NANM did not increase rates of responding but, at high doses, produced decreases in reinforcement frequency indicating that efficient timing behavior had been disrupted. These results show that although PCP, MK-801 and (+)-NANM produce generally similar behavioral effects, there may also be some differences between the compounds, notably a more consistent effect of MK-801 on punished responding. These behavioral effects may be related to antagonism of N-methyl-D-aspartate but ifenprodil, which is also an N-methyl-D-aspartate antagonist, does not show a similar behavioral profile.

Animals↗
PubMed1989

Solution structure of a tRNA with a large variable region: yeast tRNASer.

Different chemical reagents were used to study the tertiary structure of yeast tRNASer, a tRNA with a large variable region: ethylnitrosourea, which alkylates the phosphate groups; dimethylsulphate, which methylates N-7 of guanosine and N-3 of cytosine; and diethylpyrocarbonate, which modifies N-7 of adenine. The non-reactivity of N-3 of cytidine 47:1, 47:6, 47:7 and 47:8 and the reactivity of cytidine 47:3 confirms the existence of a variable stem of four base-pairs and a short variable loop of three residues. For the N-7 positions in purines, accessible residues are G1, G10, Gm18, G19, G30, I34, G35, A36, i6A37, G45, G47, G47:5, G47:9 and G73. The protection of N-7 atoms of residues G9, G15, A21, A22 and G47:9 reflects the tertiary folding. Strong phosphate protection was observed for P8 to P11, P20:1 to P22, P48 to P50 and for P59 and P60. A model was built on a PS300 graphic system on the basis of these data and its stereochemistry refined. While trying to keep most tertiary interactions, we adapted the tertiary folding of the known structures of tRNAAsp and tRNAPhe to the present sequence and solution data. The resulting model has the variable arm not far from the plane of the common L-shaped structure. A generalization of this model to other tRNAs with large variable regions is discussed.

Adenine↗
PubMed2002

Infrequent occurrence of age-dependent changes in CpG island methylation as detected by restriction landmark genome scanning.

Hypermethylation of CpG islands, resulting in the inactivation of tumor suppressor genes, is an early event in the development of some malignancies. Recent studies suggest that this abnormal methylation may be a function of aging. The number of CpG islands that methylate with age is unknown. We used restriction landmark genome scanning (RLGS) to approximate the extent to which CpG islands change methylation status during aging. Comparison of more than 2000 loci in T lymphocytes isolated from newborn, middle age, and elderly people revealed that 29 loci ( approximately 1%) changed methylation status during aging, with 23 increasing methylation, and six decreasing. The same subset also changed methylation status with age in the esophagus, lung, and pancreas, but in variable directions. Virtual genome scanning identified one of these loci as a member of the forkhead family, recently implicated in aging, and another as an EST fragment. The methylation status of both correlated with level of expression. Confirming studies in multiple tissues from normal and DNMT1(+/-) mice demonstrated only one age dependent change in the methylation of more than 2000 loci, occurring in liver and kidney. These results indicate that the methylation status of the majority of CpG islands in both mice and humans is tightly controlled during aging, and that changes are infrequent and in humans confined to a specific subset of genes.

Adult↗
PubMed1993

Selective antagonism of native and cloned kainate and NMDA receptors by polyamine-containing toxins.

Antagonism of rat excitatory amino acid receptors by a synthetic analog [philanthotoxin-343 (PhTX-343)] of a polyamine amide, wasp toxin (philanthotoxin-433) and a structurally related spider toxin, argiotoxin-636 (ArgTX-636), was examined in Xenopus oocytes injected with rat brain RNA or RNA transcribed from the excitatory amino acid receptor clones GluR1, GluR2 and NMDAR1. Antagonism of both kainate- and N-methyl-D-aspartate (NMDA)-elicited responses by PhTX-343 and ArgTX-636 was reversible, noncompetitive and partly voltage-dependent. Dose-inhibition curves were constructed using EC50 concentrations of kainate (100 microM) and N-methyl-D-aspartate (33 microM) in the presence of variable concentrations of ArgTX-636 and PhTX-343. In oocytes injected with rat brain RNA, IC50s for antagonism of kainate-induced currents were similar, i.e., 0.07 microM and 0.12 microM for ArgTX-636 and PhTX-343, respectively, whereas IC50s for antagonism of NMDA-induced currents were dissimilar, i.e., 0.04 microM for ArgTX-636 and 2.5 microM for PhTX-343. In oocytes expressing NMDAR1, IC50s were similar to those for the antagonism of NMDA-induced currents of oocytes injected with rat brain RNA. PhTX-343 and ArgTX-636 were more or less equally potent (IC50s were 2.8 microM and 3.4 microM, respectively) antagonists of the response of GluR1 to 100 microM kainate. However, GluR1 was approximately 50 times less sensitive to the toxins than non-N-methyl-D-aspartate receptors expressed in oocytes injected with rat brain RNA. Receptors co-expressed from GluR1 + GluR2 were virtually insensitive to PhTX-343 (IC50 = 270 microM) and to ArgTX-343 (IC50 approximately 300 microM).

Animals↗