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T Farkas

Publications and source records attributed to T Farkas.

At least 55 records · Page 3Linked to original sources
PubMed1997

Ether lipid composition and molecular species alterations in carp brain (Cyprinus carpio L.) during normoxic temperature acclimation.

Carp (Cyprinus carpio L.) whole brain was used to investigate the thermal acclimation changes under normoxic conditions of three-subclasses (alkenylacyl-, alkylacyl- and diacyl-subclasses) of choline glycerophospholipids (CGP), ethanolamine glycerophospholipids (EGP) and inositol glycerophospholipids (IGP) as well as their acyl chain profiles and molecular species composition. The alkenylacyl subclass of CGP and IGP and the alkylacyl subclass of CGP and EGP varied significantly during summer (25 degrees C) acclimation compared to winter (5 degrees C). The levels of alkenylacyl and alkylacyl-CGP, alkylacyl-EGP and alkenylacyl-IGP were 17.3-, 3.7-, 3.5- and 1.3-fold higher in the summer, respectively, while the alkenylacyl EGP was moderately lower. The levels of diacyl subclasses from CGP and IGP were considerably lower in the summer to compensate for the higher proportion of alkenylacyl and alkylacyl subclasses. Significant changes of ether phospholipids and the reorganization of the molecular species composition of all lipid subclasses may be associated with the "fine tuning" of the physical properties of the cellular membranes in carp brain due to temperature acclimation. The overall acyl chain profile of the three subclasses of carp brain phospholipids showed differences in composition depending upon the subclass of the individual phospholipid. Generally the polyunsaturated fatty acid (PUFA) chain composition increased relative to monounsaturated fatty acid (MUFA) and saturated fatty acids (SFA) during winter acclimation. Docosahexaenoic acid (DHA) was richer in the winter compared to summer. However, no DHA was found in ether-containing species of IGP from either winter or summer, except for 2% in alkylacyl-IGP during the summer. The above observations suggest that the content of ether phospholipids (alkenylacyl and alkylacyl) as well as the reorganization of the molecular species composition of all phospholipids may serve to maintain a functional fluid-crystalline state to preserve the signaling functions in carp brain.

Acclimatization↗
PubMed1997

Composition and Biophysical Properties of Lipids in Xenorhabdus nematophilus and Photorhabdus luminescens, Symbiotic Bacteria Associated with Entomopathogenic Nematodes.

Primary and secondary forms of Photorhabdus luminescens Hm and Xenorhabdus nematophilus N2-4 were grown at 18 and 28(deg)C for 24 to 96 h, and we made determinations of the fatty-acid compositions of total lipids and of the fluidity measured by 5-doxyl-stearic acid embedded in liposomes made from total lipids. The levels of the unsaturated fatty acids 16:1 and 18:1 (those with chain lengths of 16 or 18 and one double bond) generally were higher in primary-phase variants of P. luminescens grown at 18(deg)C than in those grown at 28(deg)C. Prolonged culture at 18(deg)C caused the level of 18:1 to fall and reach that observed at 28(deg)C. The ratio of saturated to unsaturated fatty acids rose with prolonged culture times in variants of each species at both phases. When grown at 18(deg)C, the proportion of 16:1 in X. nematophilus was lower than in P. luminescens; the patterns of temperature-induced changes were similar in these species. X. nematophilus contained a greater percentage of short-chain fatty acids (i.e., with chain lengths of <14.0) than P. luminescens. Lipid liposomes from primary and secondary cultures of both bacterial species grown at 18(deg)C were more ordered (i.e., less fluid) than those grown at 28(deg)C. This result suggests the surprising absence of homeoviscous adaptation of membranes to temperature. Also, liposomes from primary cultures were more ordered than those from secondary cultures and membranes from primary cultures of P. luminescens were more ordered at both culture temperatures than membranes from X. nematophilus. The biological significance of the effect of growth conditions on membrane biophysical properties in these bacteria is discussed.

Journal Article↗
PubMed1997

Terminal inverted repeats of insertion sequence IS30 serve as targets for transposition.

In the present study, we demonstrate that the terminal inverted repeats of the Escherichia coli insertion sequence IS30 are functional target sites for the transposition of the (IS30)2 dimer, which represents an intermediate structure in the transposition of IS30. Comparative analysis of various target regions revealed that the left and right ends differ in their "attractivity." In our experiments, the joined left and right ends, i.e., the (IS30)2 intermediate structure, was found to be the most preferred target. It was also shown that flanking sequences can influence the target activity of the terminal repeats. The functional part of the target region was localized in the inverted repeats by means of mutational analysis, and it corresponds to the binding site of IS30 transposase. Insertion of 1 bp into the right inverted repeat resulted in unusual target duplication accompanied by gene conversion. The choice of the terminal inverted repeats as targets in transposition leads to the reconstruction of the (IS30)2 structure, which may induce a cascade of further rearrangements. Therefore, this process can play a role in the evolution of the genome.

Binding Sites↗
PubMed1996

The construction and characterization of an effective transpositional system based on IS30.

We constructed an in vivo system to detect transpositional rearrangements induced by the insertion sequence IS30. The transposase protein expressed from the transposase producer plasmids catalyzed rearrangements on different target sequences presented in trans. High yields, up to 83%, of transpositional frequencies were observed. The frequency of rearrangements correlated with the amount of transposase protein produced and the attractivity of the target sequences. Alteration in the frequency of transposition was observed in the recA- E. coli strains JM109 and TG2. Remarkable structural and functional analogy was found with site-specific recombination systems.

DNA Nucleotidyltransferases↗
PubMed1996

Stimulus-dependent muscarinic effects on evoked unit activity in the rat barrel cortex.

The cerebral cortex receives a prominent cholinergic innervation, which is thought to play an important role in the regulation of its normal function. Electrophysiological studies have shown that activation of muscarinic cholinergic receptors results in a marked enhancement of excitatory stimuli onto cortical neurons. In the present study, we examined the effects of acetylcholine (ACh) and its muscarinic agonists (applied by pressure injection) on the response components of individual cortical neurons in layers IV and V of the rat somatosensory cortex in identified barrels (C2 and C3). It was found that the muscarinic agonists could modify the evoked unit activity (in most cases, they caused units to respond to previously minimally effective whisker stimuli), but the modulatory effect was highly dependent on the stimulus parameters, and in most cases, the effect was limited to only one component of 'on' or 'off' responses consisting of 2-4 spikes.

Acetylcarnitine↗
PubMed1996

The mechanism of inhibitory effect of eicosapentaenoic acid on phagocytic activity and chemotaxis of human neutrophil granulocytes.

Free eicosapentaenoic acid (EPA) was found to inhibit dose dependently the chemiluminescence of human neutrophil granulocytes phagocytosing zymosan and their chemotaxis induced by C5a-containing zymosan-activated serum (ZAS) and platelet-activating factor. Rigidification of plasma membranes in the ZAS-treated cells could be observed by measuring the fluorescence anisotropy. The cells were labeled by 3-[p-(6-phenyl-1,3,5-hexatrienoil) phenyl] propionic acid, reporting plasma membrane for determination of membrane fluidity. In resting, nonstimulated neutrophils, EPA dose dependently increased the fluidity of plasma membrane. In zymosan-activated cells, however, after a short fluidization, the basic effect of EPA was a rigidification compared to very low fluorescence anisotropy values of activated control cells. This diminished fluidity, increased membrane stability of plasma membranes can be one of the reasons for the decreased functions (phagocytosis and chemotaxis) of human EPA-treated neutrophils.

Cell Membrane↗
PubMed1996

Involvement of phospholipid molecular species in controlling structural order of vertebrate brain synaptic membranes during thermal evolution.

Fluorescence anisotropy parameter of [p-(6-phenyl)-1,3,5-hexatrienyl]phenyl-propionic acid (DPH-PA) and 1-(4-trimethylammoniumphenyl)-6-phenyl-1,3,5-hexatriene (TMA-DPH) embedded in synaptic plasma membranes prepared from brains of cold (5 degrees C) and warm (22 degrees C) adapted fish (Cyprinus carpio L.), rat (Rattus norvegicus) and bird (Branta canadensis), was studied. Fatty acid composition of total lipids as well as molecular species composition of diacyl phosphatidylcholines and phosphatidylethanolamines was also determined. The amount of long-chain polyunsaturated fatty acids decreased with increasing body temperature. There was a near-complete compensation of membrane structural order for environmental/body temperature over the evolutionary scale as seen by DPH-PA. Using TMA-DPH, the compensation was partial with rat and bird. Since DPH-PA and TMA-DPH differ in their charges, it is proposed, that the former reported membrane regions rich in cationic or zwitterionic (neutral) phospholipids and the latter, membrane regions rich in negatively charged phospholipids in the synaptic plasma membranes. Many different molecular species (20-25) of diacyl phosphatidylcholines and diacyl phosphatidylethanolamines were identified. The level of 16:0/22:6 phosphatidylcholine decreased while disaturated phosphatidylcholines increased with increase of environmental/body temperature from the fish through the bird. Level of 1-monoenoic, 2-polyenoic phosphatidylethanolamines also decreased with an increase in environmental/body temperature. Experiments using vesicles made of mixed synthetic phosphatidylcholine vesicles (16:0/16:0, 16:0/18:1, 16:0/22:6 in various proportions) showed that increase in disaturated phosphatidylcholine species does not explain the observed complete adjustment of membrane structural order in synaptic plasma membranes. Change in level of 1-monoenoic, 2-polyenoic phosphatidylethanolamines might be one of the factors involved in controlling the biophysical properties of the membrane according to the temperature.

Animals↗
PubMed1996

Serological survey on the prevalence of chicken anaemia virus infection in Hungarian chicken flocks.

A serological survey on the prevalence of chicken anaemia virus (CAV) infection was performed by using the indirect immunofluorescence (IF) and the virus neutralization (VN) tests in commercial Hungarian chicken populations. By the indirect IF test, a total of 846 serum samples from 13 meat-type parent flocks of two breeds were investigated between 10 and 62 weeks of age. All flocks were found to be positive for anti-CAV antibodies, and the rates of antibody-positive birds among flocks ranged from 40 to 93.3% and with an average of 73.3%. From nine 1-day- to 9-week-old progeny broiler flocks, 96 serum samples were tested. In the 3 flocks, sampled at the hatchery, 75 to 100% (average 86.4%) of the 22 tested birds were antibody positive. From the 6 flocks, tested between 4 to 9 weeks of age, 3 were antibody negative at 4 and 5 weeks of age, whereas in the 3 remaining 6- to 9-week-old flocks 10 to 20% (average 13.5%) of the birds were antibody positive. In egg-laying parent flocks of 14 and 35 weeks old, 54.4 and 71.7% of the tested 79 and 46 birds had antibodies to CAV, respectively. By the VN test, a total of 670 serum samples from 9 meat-type parent flocks aged between 11 and 37 weeks were investigated. The rate of antibody positivity in flocks was always over 80% and averaged 90.9%. From 7 progeny broiler flocks, 261 serum samples were tested between one day and 7 weeks of age, and the rates of seropositivity in flocks were between 93.3 to 100% and averaged 96.9%. In an egg-laying parent flock, 89.2% of the tested 102 birds had neutralizing antibodies to CAV at 35 weeks old. It was concluded that CAV is widespread in Hungarian commercial chicken populations. Though, according to simultaneous examination of 195 flock sera, the VN test revealed 11.3% more antibody-positive birds, the indirect IF test was found suitable for serological surveys at flock(s) level, provided that sufficient numbers of individual chicks were tested.

Animals↗
PubMed1996

Cloning and sequencing of the genome of chicken anaemia virus (CAV) TK-5803 strain and comparison with other CAV strains.

The complete genomic sequence of chicken anaemia virus (CAV) TK-5803 strain was determined. Comparisons of sequence data showed 37 nucleotide differences between TK-5803 and Cux-1, 38 nucleotide differences between TK-5803 and 26P4, and 48 nucleotide differences between TK-5803 and 82-2. There were 65 nucleotide differences in the largest open reading frame (ORF3) between TK-5803 and one Australian isolate. Base changes introduced amino acid changes at 6 positions in the C-terminal half of VP3, at 4 positions in the C-terminal quarter of VP2 and at 17 positions in VP1 among the strains. These indicate that the N-terminal half of VP3 and the N-terminal three quarter of VP2 are well conserved, and might sustain essential function of these proteins. The amino acid changes in VP1 which is thought to be the capsid protein may influence the antigenic character of different VP1s.

Amino Acid Sequence↗
PubMed1996

Partitioning of beta-mannanase and alpha-galactosidase from Aspergillus niger in Ucon/Reppal aqueous two-phase systems and using temperature-induced phase separation.

Enzyme partitioning and recovery with a new aqueous two-phase system based on commercially available hydroxypropyl starch Reppal PES 200 and the thermo-separating polymer Ucon 50-HB-5100 was studied. Ucon is an ethylene oxide-propylene oxide random copolymer. A culture supernatant of Aspergillus niger containing extracellular beta-mannanase and alpha-galactosidase was partitioned in two steps. The primary aqueous two-phase system contained Ucon and Reppal as phase forming polymers. The effect on enzyme partitioning of salt composition, salt concentration, pH and polymer concentration was studied with the aim of obtaining optimal partitioning of target enzymes to the phase containing the thermoseparating Ucon polymer. The partitioning of the enzymes could be strongly influenced by addition of the hydrophobic triethyl ammonium ion and the chaotropic perchlorate ion. Also the effect on cationic surfactant, cetyl trimethyl ammonium bromide, on enzyme partitioning was studied. In the second step, temperature induced phase separation was carried out on the isolated Ucon phase. A water phase and a concentrated aqueous Ucon phase were formed. The enzymes were obtained in the water phase almost free of polymer.

Aspergillus niger↗
PubMed1996

Muscarinic cholinergic effects on stimulus-evoked responses in rat primary somatosensory cortex. An electrophysiological study.

Neuron terminals originating from the nucleus basalis megnocellularis (NBM) are the major source of the cortical cholinergic innervation, which is thought to play an essential role in higher brain functions. Electrophysiological studies have shown that activation of muscarinic cholinergic receptors caused a marked enhancement of sensory stimuli onto cortical neurons. Diminished cholinergic innervation of somatosensory cortical areas are manifested in decreased stimulus-evoked activity and impaired performance in a sensory discrimination task. We examined the effects of ACh and its muscarinic agonists on the response properties of layer IV-V barrel cortex neurons evoked by precisely controlled vibriasa deflections. The cholinergic pharmacons displayed their mostly facilitatory effects in latency-dependent manner: In most cases only one latency component of On and/or Off responses were changed.

Acetylcholine↗
PubMed1995

Role of phospholipids containing docosahexaenoyl chains in modulating the activity of protein kinase C.

It is known that the phospholipids of the brain cells of fish are altered during cold adaptation. In particular, the 1-monounsaturated 2-polyunsaturated phosphatidylethanolamines (PEs) increase 2- to 3-fold upon adaptation to cold. One of the most striking changes is in the 18:1/22:6 species of PE. We determined how this lipid affected the bilayer-to-hexagonal-phase transition temperature of 16:1/16:1 PE. We found that it was more effective in lowering this transition temperature than were other, less unsaturated, PE species. In addition, it was not simply the presence of the 18:1/22:6 acyl chains which caused this effect, since the 18:1/22:6 species of phosphatidylcholine had the opposite effect on this transition temperature. Zwitterionic substances that lower the bilayer-to-hexagonal-phase transition temperature often cause an increase in the activity of protein kinase C (PKC). Indeed, the 18:1/22:6 PE caused an increase in the rate of histone phosphorylation by PKC which was greater than that caused by other, less unsaturated, PEs. The 18:1/22:6 phosphatidylcholine had no effect on this enzyme. The stimulation of the activity of PKC by the 18:1/22:6 PE is a consequence of this lipid's increasing the partitioning of PKC to the membrane.

Calorimetry, Differential Scanning↗
PubMed1995

Complex expression of murine heat shock transcription factors.

A central step in the transcriptional activation of heat shock genes is the binding of the heat shock factor (HSF) to upstream heat shock elements (HSEs). In vertebrates, HSF1 mediates the ubiquitous response to stress stimuli, while the role of a second HSE-binding factor, HSF2, is still unclear. In this work we show that both factors are expressed in a wide range of murine tissues and each exists as two splicing isoforms. Although HSFs are virtually ubiquitous proteins, their abundance is predominant in testis and variable among other tissues, indicating specific regulations of their expression. A low level of DNA-binding activity of HSF1, detected in many tissues, is probably physiological and is not explained by an anomalous regulation of one of the two isoforms. Our observations suggest that these regulatory proteins may all have roles in fully developed tissues. This possibility is not mutually exclusive of a role of HSF2 during cellular differentiation and tissue development [L. Sistonen, K. D. Sarge and R. I. Morimoto (1994), Mol. Cell. Biol., 14, 2087-2099].

Amino Acid Sequence↗
PubMed1995

Erythrocyte lipids in triose-phosphate isomerase deficiency.

Marked hypoalphalipoproteinemia was found together with relatively low serum cholesterol, triacylglycerol, and LDL levels in a triose-phosphate isomerase (TPI; D-glyceraldehyde-3-phosphate ketol-isomerase, EC 5.3.1.1)-deficient Hungarian family, especially in the two compound-heterozygote brothers. Apart from a slight increase in palmitic and stearic acids together with a slight decrease in oleic and linoleic acids, no other changes were found in the fatty acid composition of the erythrocyte phospholipids. Anisotropy measurements with n-(9-anthroyloxy) stearic and -palmitic acid fluorophores revealed increased motional freedom of the fatty acid chains in the external lipid layers of the intact erythrocytes from all members of the TPI-deficient family as compared with normal age-matched controls. This asymmetric increase in membrane fluidity was found to be significantly higher in the propositus than in his compound-heterozygote brother without any neurological disorders. The change in membrane fluidity may result from as-yet-unresolved aspects of the lipid composition of the plasma membrane. Our findings that the differences between the TPI-deficient individuals and normal controls and the differences between the two compound-heterozygote brothers were all absent in the phospholipid extracts of the same erythrocytes favor the assumption that the increased motional freedom of the fatty acid chains in the external surface of the bilayer is caused by the binding of the mutant TPI molecule to the N-terminal sequence of band 3 protein.

Adult↗
PubMed1995

Molecular architecture and biophysical properties of phospholipids during thermal adaptation in fish: an experimental and model study.

Phospholipids from livers of carps (Cyprinus carpio L.) adapted to winter (5 degrees C) and summer (25 degrees C) temperatures were isolated, and the fatty acid composition of total phospholipids, as well as molecular species composition of diacyl phosphatidylcholines and ethanolamines, were determined. Order parameter of 5-doxyl stearic acid and steady-state fluorescence anisotropy of different anthroyloxy fatty acids--[2-, 12(N-9-anthroyloxy)stearic acid and 16(N-9-anthroyloxy)palmitic acid--embedded in native and synthetic (16:0/16:0, 16:0/22:6, 18:0/22:6, 18:1/22:6, 20:4/20:4, 22:6/22:6 phosphatidylcholines and 16:0/18:1, 18:1/22:6 phosphatidylethanolamines) phospholipid vesicles was also determined between -30 and 30 degrees C and 5 and 30 degrees C, respectively. There is an accumulation of 1-monoenoic, 2-polyenoic diacyl phosphatidylcholine and ethanolamine with a concomitant reduction of 1-stearoyl,2-docosahexaenoyl species in the cold-adapted state. Despite a 30% accumulation of long-chain polyunsaturated fatty acids in phospholipids in cold, there is only a 5 degrees C downshift in the solid-gel to liquid-crystalline phase transition temperature (-8 vs. -13 degrees C). Vesicles from total phospholipids of cold-adapted fish proved to be more disordered in all segments than from the warm-adapted ones when assayed using 2,12-(N-9-anthroyloxy)stearic and 16-(N-9-anthroyloxy)palmitic acid. Vesicles made from purified phosphatidylcholines showed the same pattern, but they were more disordered than the corresponding total phospholipids. This could be modelled using mixed phospholipid vesicles made of synthetic 16:0/22:6 phosphatidylcholine (75%) and either 18:1/22:6 phosphatidylethanolamine (25%) vs. 16:0/18:1 phosphatidylethanolamine (25%) and comparison of the anisotropy parameters of 100% 16:0/22:6 and 100% 18:1/22:6 phosphatidylcholine vesicles. Mixing either 16:0/18:1 (25%) or 18:1/22:6 (25%) phosphatidylethanolamines to 18:0/22:6 (75%) phosphatidylcholine shifted down or up, respectively, the transition temperature of vesicles compared to 100% 18:0/22:6 vesicles assayed by electron spin resonance spectroscopy using 5-doxylstearic acid. It is concluded that it is not the gross amount of long-chain polyunsaturated fatty acids in phospholipids, but rather their specific combination with cis delta 9 monounsaturated fatty acids in the position sn-1, especially in phosphatidylethanolamines, that is important in determining the physical properties of biomembranes in relation to adaptational temperature.

Adaptation, Physiological↗
PubMed1994

Spin label EPR study of lipid solvation of supramolecular photosynthetic protein complexes in thylakoids.

Lipid-protein association in the chloroplast membrane and its various thylakoid fractions from higher plants, namely pea and maize, rich in Photosystem I (PSI) and Photosystem II (PSII), respectively, were studied using EPR spectroscopy of spin-labelled lipid molecules. All the EPR spectra consisted of two spectral components corresponding to bulk fluid lipids and solvation lipids motionally restricted at the hydrophobic surface of membrane proteins. Spin-labelled stearic acid and phosphatidylglycerol exhibited marked selectivity towards the supramolecular protein complexes of both PSI and PSII although to different extent. In addition, lipid-protein titration experiments are described for partially delipidated PSII-enriched membrane fractions of pea chloroplasts, incorporating unlabelled egg phosphatidylcholine prior to or after the incorporation of spin-labelled lipids. Two sets of solvation sites were resolved by timed labelling experiments and a significant result of these studies was that a well-defined population of solvation sites (approx. 100 mol lipids/820 kDa protein) was rapidly exchanged by laterally diffusing membrane lipids, while other solvation sites (approx. 50 mol lipids/820 kDa protein) were exchanged much slower or not exchanged at all.

Chloroplasts↗
PubMed1994

Structural order of membranes and composition of phospholipids in fish brain cells during thermal acclimatization.

A comparison of the structural orders of membranes of a mixed brain-cell population isolated from Cyprinus carpio L. acclimated to either summer (23-25 degrees C) or winter (5 degrees C) revealed a high degree of compensation (80%) for temperature, as assayed by electron spin resonance spectroscopy. The cells rapidly forget their thermal history and adjust the physical properties of the membranes when shifted to the other extreme of temperature either in vivo or in vitro. Phospholipids separated from both types of animals exhibit only around 10% compensation. Arachidonic and docosahexaenoic acids are the major polyunsaturated fatty acids in the brains, but the fatty acid composition of the brain total phospholipids does not vary with adaptation to temperature. Separation of phosphatidylcholines and phosphatidylethanolamines into molecular species revealed a 2- to 3-fold accumulation of 18:1/22:6, 18:1/20:4, and 18:1/18:1 species in the latter; 18:0/22:6 showed an opposite tendency. Molecular species composition of phosphatidylcholines did not vary with the temperature. The same trends of changes were seen with brains of freshwater fish from subtropical (Catla catla L.) or boreal (Acerina cernua) regions. It is concluded that the gross amount of docosahexaenoic acid (22:6) plays only a minor role in adjusting the membrane physical properties to temperature. Factors other than lipids might be involved in the adaptation processes. Due to their specific molecular architecture, molecules such as 18:1/22:6, 18:1/20:4, or 18:1/18:1 phosphatidylethanolamine might prevent the contraction of membranes in the cold and may provide an environment for some other components involved in the temperature regulation of physical properties of nerve cell membranes.

Acclimatization↗