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At least 145 records · Page 8Linked to original sources

PubMed2000

Energy consumption and exhaust emissions in mechanized timber harvesting operations in Sweden.

The study presents an estimation of the energy input and the amount of emissions to air due to fuel, chainsaw and hydraulic oil consumption by heavy duty diesel engine vehicles operating in forest logging operations in Sweden. Exhaust concentrations are given for carbon dioxide, carbon monoxide, nitrogen oxides, hydrocarbons and particulate matter. Three fuel types (rapeseed methyl ester, environmental class 1 and environmental class 3 diesel fuels) and two types of lubricating base oil (mineral- and vegetable-based) were examined. Energy input per unit of timber production (m3ub) was 82 MJ, 11% of which was due to energy consumption during the production phase of the fuel. Emissions during the whole life cycle of the fuels and the base oils are included in the study. The highest CO2 and NOx emissions occurred when rapeseed methyl ester was used as fuel together with rapeseed as base oil for chainsaw and hydraulic oil. The highest HC and CO emissions occurred when environmental class 3 diesel fuel was used.

Air Pollutants, Occupational↗

PubMed1979

DNA methylation: organ specific variations in the methylation pattern within and around ovalbumin and other chicken genes.

The restriction enzymes HhaI and HpaII, whose activity is inhibited by cytosine methylation within their recognition sites, have been utilised as probes to study methylation in the vicinity of the ovalbumin gene in DNA from various chicken tissues. This was complemented by a preliminary study of methylation in the regions of chicken ovotransferrin (conalbumin), ovomucoid and beta-globin genes. From our data we conclude that HaI or HpaII sites can be divided in 3 classes according to their pattern of methylation in different tissues. In the first class of sites (mV class) the extent of methylation varies in different tissues. The patterns obtained show that methylation at the sites located within and around the 3 genes which code for egg white proteins is in general lowest in oviduct of laying hen, where these genes are expressed. However some sites are not methylated (m- class) and others are 95 to 100% resistant (m+ class) to digestion by HhaI or HpaII in the DNAs of all the tissues which were tested. Our study has also revealed a remarkable number of allelic variants for the presence of HhaI or HpaII sites in the region of the ovalbumin gene.

Animals↗

PubMed2006

Tudor, MBT and chromo domains gauge the degree of lysine methylation.

The post-translational modification of histones regulates many cellular processes, including transcription, replication and DNA repair. A large number of combinations of post-translational modifications are possible. This cipher is referred to as the histone code. Many of the enzymes that lay down this code have been identified. However, so far, few code-reading proteins have been identified. Here, we describe a protein-array approach for identifying methyl-specific interacting proteins. We found that not only chromo domains but also tudor and MBT domains bind to methylated peptides from the amino-terminal tails of histones H3 and H4. Binding specificity observed on the protein-domain microarray was corroborated using peptide pull-downs, surface plasma resonance and far western blotting. Thus, our studies expose tudor and MBT domains as new classes of methyl-lysine-binding protein modules, and also demonstrates that protein-domain microarrays are powerful tools for the identification of new domain types that recognize histone modifications.

Histones↗

PubMed2006

Inhibition of MHC class II gene expression in uveal melanoma cells is due to methylation of the CIITA gene or an upstream activator.

Most cells with an intact interferon-gamma receptor and signaling pathway are able to express MHC class II molecules when treated with cytokines such as interferon-gamma and tumor necrosis factor-a. Interestingly, primary uveal melanocytes and most ocular melanoma cells are resistant to interferon-gamma mediated induction of class II MHC genes. This unusual phenotype is hypothesized to be germane to the immune-privileged status to the eye. Via a series of experiments, we have probed the molecular basis of this class II MHC resistant phenotype. We have analyzed the methylation status of the gene encoding the class II transactivator (CIITA), and asked whether treatment of class II MHC resistant ocular melanoma cells with the demethylating agent 5'-azacytidine can restore interferon-gamma inducibility of these class II MHC genes in these cells. The data obtained suggest that the specific blockade in cytokine-induced class II MHC gene expression is due to a suppression of the gene encoding the class II transactivator (CIITA). Treatment with 5' azacytidine restores the ability of these cells to express class II MHC genes upon interferon-gamma treatment. Whilst this is reminiscent of what occurs in another immune-privileged tissue--the placental trophoblast--we show here that silencing of the CIITA gene in uveal melanocytes either involves methylation of distinct nucleotides from those detected in trophoblasts, or involves an upstream activator of CIITA gene expression.

Azacitidine↗

PubMed2006

Cognitive dysfunction in schizophrenia: convergence of gamma-aminobutyric acid and glutamate alterations.

Impairments in certain cognitive functions mediated by the dorsolateral prefrontal cortex, such as working memory, are core features of schizophrenia. Convergent findings suggest that these disturbances are associated with alterations in markers of inhibitory gamma-aminobutyric acid and excitatory glutamate neurotransmission in the dorsolateral prefrontal cortex. Specifically, reduced gamma-aminobutyric acid synthesis is present in the subpopulation of gamma-aminobutyric acid neurons that express the calcium-binding protein parvalbumin. Despite presynaptic and postsynaptic compensatory responses, the resulting impaired inhibitory regulation of pyramidal neurons contributes to a reduction in the synchronized neuronal activity that is required for working memory function. Several lines of evidence suggest that these changes may be either secondary to or exacerbated by impaired signaling via the N-methyl-d-aspartate class of glutamate receptors. These findings suggest specific targets for therapeutic interventions to improve cognitive function in individuals with schizophrenia.

Animals↗

PubMed1982

Methylation of ribonucleic acid in a cell-free system from mouse myeloma cells.

Isolated nuclei incorporate few methyl groups into RNA when they are incubated with S-adenosyl[methyl-3H3]methionine and four ribotriphosphates. When the nuclei were supplemented with a soluble total cell protein extract, the incorporation of methyl groups into RNA was stimulated 3-6-fold. All classes of RNA were methylated. Methylation of the 2'-OH of ribose and the bases of ribosomal RNA occurred predominantly on endogenous ribosomal RNA precursors, with a minority (20%) occurring on the newly synthesized rRNA precursor. Methylation of the tRNA precursor occurred on both endogenous (40%) and newly synthesized (60%) molecules. The methylation of adenosine in hnRNA occurred predominantly on molecules transcribed in vitro and was sensitive to 1 microgram/mL alpha-amanitin. A final site of methylation was the 7 position of guanosine of the cap structure. About 10% of the RNA polymerase II transcripts were capped in vitro. Capping was blocked 90% by 1 microgram/mL alpha-amanitin and was independent of the presence of the cell protein extract.

Animals↗

PubMed1989

A novel class of local antiinflammatory steroids. 1st communication: analogues of methyl 11 beta,17 alpha,21-trihydroxy-3,20-dioxo-pregna-1,4-diene-16 alpha-carboxylate.

A novel class of steroidal 16-esters and amides, 1-8 has been synthesized and evaluated as safer local antiinflammatory agents. These compounds retain the intact ketol side-chain of prednisolone and have an alkanoate ester or carboxamide function at the C-16 of the steroid nucleus. In the cotton pellet granuloma assay a correlation was observed between the size of the C-16 substituent group and the local antiinflammatory activity. The incorporation of a methyl carboxylate group at the C-16 position of prednisolone as in methyl 11 beta,17 alpha,21-trihydroxy-3,20-dioxo-pregna-1,4-diene-16 alpha-carboxylate, 5, resulted in an increase in antiinflammatory activity. The 17-deoxy analogue of 5, 1, retained one-half the activity of prednisolone. These two compounds were further evaluated for their effects on plasma corticosterone, adrenal and thymic weights at their ID50 doses for granuloma formation. Neither 5 nor 1 depressed plasma corticosterone levels or significantly altered adrenal weights. Compound 1 was also devoid of thymolytic activity, whereas 5 produced a 33% thymic involution at its ID50 compared to 47% for prednisolone at its equiactive dose.

Adrenal Glands↗

PubMed1984

Cyclic GMP may serve as a second messenger in peptide-induced muscle degeneration in an insect.

At the end of metamorphosis, the intersegmental muscles of the moth Antheraea polyphemus undergo rapid degeneration in response to the peptide eclosion hormone (EH). Muscle death was preceded by a 22-fold increase in muscle guanosine-3',5'-cyclic monophosphate (cGMP) titers, which peaked 60 min after peptide exposure; adenosine-3'5'-cyclic monophosphate (cAMP) titers remained unchanged. EH induced a dose-dependent increase in muscle cGMP content with a threshold dose similar to that needed to induce cell death. Exogenous cGMP, but not cAMP, mimicked the action of EH. Sodium nitroprusside, a potent stimulator of guanylate cyclase, and methylated xanthines, a class of 3',5'-cyclic-nucleotide phosphodiesterase inhibitors, also induced the selective death of these muscles. It is concluded that an elevation of cGMP level is involved in EH-induced muscle degeneration. The intersegmental muscles become sensitive to EH at the end of adult development in response to the declining titers of the steroid molting hormones, the ecdysteroids. At earlier times, treatment with EH, exogenous cGMP, sodium nitroprusside, or methylated xanthines was ineffective in causing cell death. Nevertheless, treatment with EH at this time resulted in a marked increase in intersegmental-muscle cGMP. Thus, the onset of physiological responsiveness to the peptide hormone presumably results from biochemical changes distal to the EH receptors and guanylate cyclase.

3',5'-Cyclic-AMP Phosphodiesterases↗

PubMed1997

The phospholipid methyltransferases in yeast.

In fungal microorganisms including fission yeast, Schizosaccharomyces pombe and baker's yeast, Saccharomyces cerevisiae, two enzymes are required to catalyze the synthesis of phosphatidylcholine (PC) from phosphatidylethanolamine (PE). The genes encoding the class I and class II phospholipid N-methyltransferases (PLMTs) have been cloned from both yeasts. The class II PLMTs catalyze the first methylation step from PE to phosphatidyl-monomethylethanolamine (PMME). Representatives of the class II type enzymes have been isolated only from yeast and the amino acid sequence of these enzymes contain regions of internal duplication. The class I PLMTs catalyze the last two methylation steps from PMME to PC. The class I PLMTs from both yeasts are homologous to the products of the phosphatidylethanolamine methyltransferase (PEMT) genes isolated from mouse and rat (described in the article by Vance et al. in this volume). Like the mammalian PEMT gene products, the S. cerevisiae class I enzyme can catalyze all three methylation steps to PC biosynthesis. S. cerevisiae strains, in which either the class II or class I enzyme is deleted, grow slowly in the absence of choline and exhibit low levels of PC. However, in S. pombe, mutants lacking either one of the two PLMTs are choline auxotrophs. Thus, both enzymes are required in S. pombe for maximal growth in the absence of exogenous choline. The S. cerevisiae methyltransferase genes are regulated at the level of transcription in response to the soluble precursors, inositol and choline as well as to growth phase. The mechanism of regulation of the S. pombe methyltransferases is not yet understood but appears to occur post-transcriptionally in response to choline availability. In addition, the S. pombe PLMT genes are regulated transcriptionally in response to growth phase.

Amino Acid Sequence↗

PubMed1992

A novel fluorescent fatty acid, 5-methyl-BDY-3-dodecanoic acid, is a potential probe in lipid transport studies by incorporating selectively to lipid classes of BHK cells.

The 5-methyl-BDY-3-dodecanoic acid (B12FA) labelling of BHK cell lipids was analyzed by thin layer and reverse phase column chromatography. Incorporation to phospholipids was selective: over 90% of B12FA label was enriched in phosphatidylcholine. The major molecular species of PC was that containing palmitate as the unlabelled fatty acid. Small amounts of label was also found in other phosphoglycerides, but not in sphingomyelin. Triglycerides and diglycerides constituted the main B12FA-labelled neutral lipid classes; however, no label was found in cholesterol esters. B12FA was degraded to shorter homologues, which had significantly slower lipid incorporation rates. B12FA-labelled cells displayed in a microscope initially green reticular type fluorescence, but later red spherical structures, representing neutral lipid droplets, could also be seen. It is concluded that B12FA does not incorporate indiscriminately to all lipid classes of BHK cells, but is enriched to PC, diglycerides and triglycerides, which could be utilized in studies on lipid transport as well as metabolism.

Animals↗

PubMed1991

Separation of alpha 1 adrenergic and N-methyl-D-aspartate antagonist activity in a series of ifenprodil compounds.

Ifenprodil (1) represents a new class of N-methyl-D-aspartate (NMDA) antagonist. This drug also possesses potent activity at several other brain receptors (most notably alpha 1 adrenergic receptors). We have prepared the enantiomers and diastereomers of ifenprodil along with a series of partial structures in order to explore the basic structure activity relations within this class of compounds. From this study, it is clear that alpha 1 adrenergic and NMDA receptor activities may be separated by selection of the threo relative stereochemistry. Examination of the optical isomers of threo-ifenprodil (2) reveals that no further improvement in receptor selectivity is gained from either antipode. Individual removal of most of the structural fragments from the ifenprodil molecule generally results in less active compounds although fluorinated derivative 9 with threo relative stereochemistry is somewhat more potent and substantially more selective for the NMDA receptor. Finally a minimum structure for activity in this series (14) has been identified. This stripped-down version of ifenprodil possesses nearly equivalent affinity for the NMDA receptor with no selectivity over alpha 1 adrenergic receptors.

Adrenergic alpha-Antagonists↗

PubMed1990

The MHC class II deficiency syndrome: heterogeneity at the level of the response to 5-azadeoxycytidine.

The involvement of DNA methylation in aberrant MHC class II gene expression in EBV-transformed B-cell lines from 2 patients (THF and DGN) with the MHC class II deficiency syndrome (bare lymphocyte syndrome) was investigated. Incubation of the cells in the presence of various concentrations of 5-azadeoxycytidine resulted in the induction of expression of HLA DR genes in the DGN cell line, whereas, in the THF cell line, no effect of 5-azadeoxycytidine treatment on the expression of the HLA DR genes could be detected. Subsequent Southern blot analysis using methylation-sensitive restriction enzymes (ApyI, EcoRII and HhaI) and 5-azadeoxcycytidine-treated and untreated genomic DNA, indicated that the lack of HLA DR-A expression in the DGN cell line is not caused by hypermethylation of the 5' region of the HLA DR-A gene. These results indicate that 5-azadeoxycytidine treatment of the DGN cell line leads to activation of a methylation-sensitive factor that is involved in the regulation of transcription of the DR-A gene. In cell line THF, however, demethylation does not restore the activity of this factor. The lack of MHC class II expression in this cell line is caused by some other defect. The results of our analysis indicate that at least two different factors are involved in regulation of MHC class II gene expression.

Azacitidine↗

PubMed1989

DNA methylation and the regulation of gene expression.

An inverse relationship between a eukaryotic gene's level of methylation and its level of expression has long been recognized, and generally believed to result from reduced binding of postulated activator proteins to methylated target DNAs. There are, however, some genes where there is no apparent correlation between levels of methylation and gene expression, and even a small class where gene activation is correlated with increased methylation of the DNA. I propose a unifying hypothesis to explain these apparently divergent cases: methylation acts to reduce or abolish binding of regulatory proteins to their DNA target sites. In the majority of genes, methylation acts to block binding of activating factors; "indifferent" genes lack such methylation sites, while the minority class, which is more active when methylated, contains methylation sites which block binding of repressor proteins.

DNA↗

PubMed2006

Effects of calcium binding on the side-chain methyl dynamics of calbindin D9k: a 2H NMR relaxation study.

The effects of Ca(2+) binding on the side-chain methyl dynamics of calbindin D(9k) have been characterized by (2)H NMR relaxation rate measurements. Longitudinal, transverse in-phase, quadrupolar order, transverse anti-phase and double quantum relaxation rates are reported for both the apo and Ca(2+)-loaded states of the protein at two magnetic field strengths. The relatively large size of the data set allows for a detailed analysis of the underlying conformational dynamics by spectral density mapping and model-free fitting procedures. The results reveal a correlation between a methyl group's distance from the Ca(2+) binding sites and its conformational dynamics. Several methyl groups segregate into two limiting classes, one proximal and the other distal to the binding sites. Methyl groups in these two classes respond differently to Ca(2+) binding, both in terms of the timescale and amplitude of their fluctuations. Ca(2+) binding elicits a partial immobilization among methyl groups in the proximal class, which is consistent with previous studies of calbindin's backbone dynamics. The distal class, however, exhibits a trend that could not be inferred from the backbone data in that its mobility actually increases with Ca(2+) binding. We have introduced the term polar dynamics to describe this type of organization across the molecule. The trend may represent an important mechanism by which calbindin D(9k) achieves high affinity binding while minimizing the corresponding loss of conformational entropy.

Animals↗

PubMed1988

DNA methylation prevents transfection of genes for specific surface antigens.

Sperm and trophoblast are among the few nucleated human cells that do not express HLA class I antigens. DNA methylation, which is proposed to be a tight mechanism of regulation, may be necessary to turn off these genes. We have investigated the transfectability of HLA class I genes and of the genes for the T-cell differentiation antigens Leu-1 (CD5) and Leu-2 (CD8) in mouse L cells by using human sperm cells and choriocarcinoma cell lines, tumors of trophoblastic origin, as sources of DNA. It was found that DNA from one choriocarcinoma line (JAR) does not transfect genes for HLA, Leu-1, or Leu-2 and that DNA from two other choriocarcinoma lines (BeWo and Ima) transfects only some of the surface markers. Sperm DNA transfects genes for all the surface antigens tested except Leu-1. DNA from control cells and from the line SCH transfects all the markers studied. Southern blots show that all cell types contain apparently intact genes encoding HLA, Leu-1, and Leu-2 and reveal differences in the DNA methylation patterns of genes from different sources of DNA. We treated JAR (the cell line with the lowest transfecting ability) with 5-azacytidine and obtained demethylation of its DNA. This demethylated DNA transfects genes for both HLA class I antigens and Leu-2. Further culture of JAR cells in the absence of 5-azacytidine results in remethylation of their DNA and decreased ability to transfect these surface antigens. These findings indicate that DNA methylation affects the efficiency of transfection of surface antigen genes in L cells.

Cell Line↗

PubMed1997

Crystal structure of the chemotaxis receptor methyltransferase CheR suggests a conserved structural motif for binding S-adenosylmethionine.

BACKGROUND: Flagellated bacteria swim towards favorable chemicals and away from deleterious ones. The sensing of chemoeffector gradients involves chemotaxis receptors, transmembrane proteins that detect stimuli through their periplasmic domains and transduce signals via their cytoplasmic domains to the downstream signaling components. Signaling outputs from chemotaxis receptors are influenced both by the binding of the chemoeffector ligand to the periplasmic domain and by methylation of specific glutamate residues on the cytoplasmic domain of the receptor. Methylation is catalyzed by CheR, an S-adenosylmethionine-dependent methyltransferase. CheR forms a tight complex with the receptor by binding a region of the receptors that is distinct from the methylation site. CheR belongs to a broad class of enzymes involved in the methylation of a variety of substrates. Until now, no structure from the class of protein methyltransferases has been characterized. RESULTS: The structure of the Salmonella typhimurium chemotaxis receptor methyltransferase CheR bound to S-adenosylhomocysteine, a product and inhibitor of the methylation reaction, has been determined at 2.0 A resolution. The structure reveals CheR to be a two-domain protein, with a smaller N-terminal helical domain linked through a single polypeptide connection to a larger C-terminal alpha/beta domain. The C-terminal domain has the characteristics of a nucleotide-binding fold, with an insertion of a small antiparallel beta sheet subdomain. The S-adenosylhomocysteine-binding site is formed mainly by the large domain, with contributions from residues within the N-terminal domain and the linker region. CONCLUSIONS: The CheR structure shares some structural similarities with small molecule DNA and RNA methyltransferases, despite a lack of sequence similarity among them. In particular, there is significant structural preservation of the S-adenosylmethionine-binding clefts; the specific length and conformation of a loop in the alpha/beta domain seems to be required for S-adenosylmethionine binding within these enzymes. Unique structural features of CheR, such as the beta subdomain, are probably necessary for CheR's specific interaction with its substrates, the bacterial chemotaxis receptors.

Amino Acid Sequence↗

PubMed2003

Class I chitinase and beta-1,3-glucanase are differentially regulated by wounding, methyl jasmonate, ethylene, and gibberellin in tomato seeds and leaves.

Class I chitinase (Chi9) and beta-1,3-glucanase (GluB) genes are expressed in the micropylar endosperm cap of tomato (Lycopersicon esculentum) seeds just before radicle emergence through this tissue to complete germination. In gibberellin (GA)-deficient mutant (gib-1) seeds, expression of Chi9 and GluB mRNA and protein is dependent upon GA. However, as expression occurs relatively late in the germination process, we investigated whether the genes are induced indirectly in response to tissue wounding associated with endosperm cap weakening and radicle protrusion. Wounding and methyl jasmonate (MeJA) induced Chi9 expression, whereas ethylene, abscisic acid, sodium salicylate, fusicoccin, or beta-aminobutyric acid were without effect. Chi9 expression occurred only in the micropylar tissues when seeds were exposed to MeJA or were wounded at the chalazal end of the seed. Expression of Chi9, but not GluB, mRNA was reduced in germinating seeds of the jasmonate-deficient defenseless1 tomato mutant and could be restored by MeJA treatment. Chi9 expression during germination may be associated with "wounding" from cell wall hydrolysis and weakening in the endosperm cap leading to radicle protrusion, and jasmonate is involved in the signaling pathway for this response. Among these treatments and chemicals (other than GA), only MeJA and wounding induced a low level of GluB expression in gib-1 seeds. However, MeJA, wounding, and particularly ethylene induced both genes in leaves, whereas GA induced only Chi9 in leaves. Although normally expressed simultaneously during tomato seed germination, Chi9 and GluB genes are regulated distinctly and tissue specifically by hormones and wounding.

Abscisic Acid↗

PubMed1999

The modulatory effect of spermine on the glutamate-NMDA receptor is regionally variable in normal human adult cerebral cortex.

The MK-801, glutamate and polyamine binding sites on the N-methyl-D-aspartate class of glutamate receptors labelled with [3H]MK-801 were characterized in four cortical areas (sensorimotor, superior temporal, mid-frontal and occipital) from seven human adult control cases. Age, post-mortem delay, tissue storage time and sex had no significant effects on any of the parameters measured. Dissociation constants (K(D) values) for MK-801 showed similar mean values in the four cortical areas, whereas receptor densities (B(max) values) showed significant differences between sensorimotor or occipital and superior temporal or mid-frontal cortex. There were marked regional differences in the profiles of the spermine- and glutamate-incremented enhancement of specific [3H]MK-801 binding. The EC(50) for the glutamate enhancement was significantly higher in the occipital than in the mid-frontal and sensorimotor cortex, whereas maximal glutamate-enhanced binding values did not differ. The maximal enhancement of [3H]MK-801 binding by spermine and glutamate varied between the cases, ranging from zero to 40.4+/-9.3 fmol x mg protein(-1) for spermine, and from 85+/-5 to 111+/-10 fmol x mg protein(-1) for glutamate. Maximal spermine enhancement of [3H]MK-801 binding was significantly more variable in superior temporal or mid-frontal than in sensorimotor or occipital cortex. The results suggest that N-methyl-D-aspartate receptor sites, especially the polyamine site, are heterogeneous in human cerebral cortex, and show a high degree of regional and individual variability.

Age Factors↗