PubMed Health⌕ Search

Biomedical subjects

S Lakatos

Publications and source records attributed to S Lakatos.

At least 19 recordsLinked to original sources
PubMed1997

Time-distance relations in shifting attention between locations on one's body.

Does the time to discriminate the presence or absence of a tactile stimulus depend on its distance from the bodily location to which one has been attending? Subjects were tested by the presentation of air puffs at four of eight possible locations on the body. In each trial of Experiment 1, (1) subjects attended auditorily to an announcement of one of the eight locations; (2) 2 sec later, a second location was announced and, simultaneously, air puffs were presented at a randomly selected four of the eight locations; (3) the subjects reported as quickly as possible on whether or not air puffs had been presented at the second-announced location. Overall, reaction times increased with the distance between the just-attended and the tested locations. Experiment 2 was undertaken to determine whether the operative distance was distance through the subject's body or directly through three-dimensional space. The subjects were tested as in Experiment 1, but with their arms and legs either side-by-side in front or spread out to each side. Reaction times then depended more on straight-line distance in space than on distance through the body.

Adult↗
PubMed1995

Noncovalent interactions in maintaining the native structure of low density lipoprotein.

The integrity and the surface charge distribution of native low density lipoprotein (LDL) are prerequisites of its binding to the LDL receptor. Oxidation is one of the most important physiological effects resulting in an altered structure and metabolism of LDL. To reveal forces responsible for maintaining the intact structure of LDL in the absence of cells we have determined the kinetics of lipid peroxidation, changes in electrophoretic mobilities and size distributions of LDL samples as a function of Cu++ induced oxidative modification in a cell-free system at two different (50 mM and 150 mM) ionic strengths by electrophoretic and dynamic light scattering. Our data show that the lipid peroxidation is almost complete before LDL is degraded at 50 mM while a slight extent of lipid peroxidation is enough to result in the same effect at 150 mM. These suggest that both ionic and hydrophobic interactions are necessary to maintain the integrity of the LDL molecule.

Centrifugation, Density Gradient↗
PubMed1995

The influence of visual cues on the localisation of circular auditory motion.

A relative inability of listeners to refer auditory motion properly to the front hemifield when a rapid circular trajectory is traced around them in the horizontal plane was investigated. It was hypothesised that the representations of visual space and auditory frontal space are linked in such a way that auditory cues alone are insufficient to determine the veridical path in the front hemifield when both the front and the rear hemifield receive circular auditory input in rapid sequence. Listeners discriminated the direction of a rapid apparent trajectory created by the sequential activation of various combinations of loudspeakers and light-emitting diodes spaced evenly in a circular array. The addition of visual stimuli to the front hemifield, even when lacking motional cues, improved discrimination significantly. Conversely, when the same portion of the trajectory presented to the front hemifield consisted only of visual stimuli, performance decreased markedly. Additional conditions, in which the trajectory was restricted to a 120 deg path in the frontal plane, confirmed these effects. The findings suggest that the presence of a visual cue enhances the perception of auditory directionality, even when it does not itself provide any motion information.

Adult↗
PubMed1993

Recognition of complex auditory-spatial patterns.

Two experiments were carried out to investigate the perception of complex auditory-spatial patterns. Subjects were asked to identify alphanumeric characters whose patterns could be outlined acoustically through the sequential activation of specific units in a speaker array. Signal bandwidths were varied systematically in both experiments. Signals in experiment 1 had sharp onsets and offsets; envelope shapes in experiment 2 were much more gradual. Subjects showed considerable ability in recognizing alphanumeric patterns traced with signals of varying acoustical composition. Reductions in the steepness of signal attack and decay produced limited declines in pattern recognition ability. Systematic trends in the relation between patterns and the distribution of incorrect responses suggest that subjects performed a pattern-matching task, in which identifications were made on the basis of component features. The unexpected pattern recognition abilities that subjects demonstrated in both experiments suggest that spatial hearing, like vision, has access to mechanisms for amodal spatial representations.

Adult↗
PubMed1993

Temporal constraints on apparent motion in auditory space.

The hypothesis that the extent of spatial separation between successive sound events directly affects the perception of time intervals between these events was tested using an apparent motion paradigm. Subjects listened to four-tone pitch patterns whose individual tones were sounded alternately at one of two loudspeaker positions, and they adjusted the alternation rate until they could no longer distinguish the four-tone ordering of the pattern. Four horizontal and two vertical loudspeaker separations were tested. Results indicate a direct relation between horizontal separation and the critical stimulus onset asynchrony (SOA) between successive tones within a pattern. At the critical SOA, subjects reported hearing not a four-tone pattern, but two pairs of two-note groups overlapping in time. The findings are discussed in the context of auditory spatial processing mechanisms and possible sensory-specific representational constraints.

Attention↗
PubMed1991

Interactions between globular proteins and F-actin in isotonic saline solution.

Solutions of each of three different globular proteins (cytochrome c, chromophorically labeled serum albumin, and chromophorically labeled aldolase), mixed with another unlabeled globular protein or with fibrous actin, were prepared in pH 8.0 Tris-HCl buffer containing 0.15 M NaCl. Each solution was centrifuged at low speed, at 5 degrees C, until unassociated globular protein in solution achieved sedimentation equilibrium. Individual absorbance gradients of both macrosolutes in the mixtures subsequent to centrifugation were obtained via optical scans of the centrifuge tubes at two wavelengths. The gradients of each macrosolute in mixtures of two globular proteins revealed no association of globular proteins under the conditions of these experiments, but perturbation of the gradients of serum albumin, aldolase, and cytochrome c in the presence of F-actin indicated association of all three globular proteins with F-actin. Perturbation of actin gradients in the presence of serum albumin and aldolase suggested partial depolymerization of the F-actin by the globular protein. Analysis of the data with a simple phenomenological model relating free globular protein, bound globular protein, and total actin concentration provided estimates of the respective equilibrium constants for association of serum albumin and aldolase with F-actin, under the conditions of these experiments, of the order of 0.1 microM-1.

Actins↗
PubMed1991

Substrate channeling in glycolysis: a phantom phenomenon.

It has been proposed that glycolytic enzymes form multienzyme complexes for direct transfer of metabolites from the producing enzyme to the utilizing one. Reexamination of the supporting evidence, which involves the transfer of NADH between its complexes with glycerol-3-phosphate dehydrogenase (alpha-glycerol phosphate dehydrogenase, GPDH; EC 1.1.1.8) and with L-lactate dehydrogenase (LDH; EC 1.1.1.27), has shown that the supporting evidence is based on misinterpretation of the kinetics of ligand exchange. Srivastava et al. have responded with a revision of their own and criticism of our data. To clarify this problem, we have carried out detailed kinetic studies on NADH binding to GPHD and LDH and on the displacement of enzyme-bound NADH by LDH or GPDH. The experiments were conducted at 10 degrees C in 50 mM Hepes, pH 7.5/100 mM KCl/1 mM EDTA/1 mM 2-mercaptoethanol, using rabbit muscle GPDH and LDH. The results show that the kinetic patterns exhibited by the displacement of NADH-bound enzyme by either GPDH or LDH are consistent with a dissociative mechanism but not with a direct transfer mechanism. Theoretical analysis shows that a combined dissociative and direct transfer mechanism can explain the transient kinetic data reported by Srivastava et al. if, and only if, a majority (approximately 90%) of the enzyme present in lower concentration exists as a complex with the second enzyme. However, data from tracer and traditional sedimentation equilibrium and from gel filtration experiments show that LDH and GPDH do not form complexes in the presence of saturating NADH concentration when the enzyme concentrations are ranged between 4 and 50 microM, a concentration equal to or greater than that used by Srivastava et al. Our results demonstrate that GPDH and LDH do not form multienzyme complex and the transfer of NADH between these enzymes proceeds via a dissociative mechanism.

Animals↗
PubMed1991

Structural rearrangements in active and inactive forms of hydrogenase from Thiocapsa roseopersicina.

The electrophoretic behavior of Thiocapsa roseopersicina hydrogenase on sodium dodecyl sulfate gels demonstrates that the protein exists in two active forms, A1 and A2, which may be interconverted. Each of these forms has a characteristic electrophoretic mobility and differs in its sensitivity to O2. Form A1 is O2-labile and converts to A2 under O2. Form A2 is less sensitive to O2 and may be converted into A1 under H2 atmosphere. Both active forms are present in aerobically isolated samples. Because the proteins are still active on 15% sodium dodecyl sulfate gels, they are not completely denatured, and the apparent molecular masses do not necessarily represent the true molecular masses of the enzymes. A1 has an Rf = 0.19, corresponding to an apparent molecular mass of 90 kDa, and A2 has an Rf = 0.35, corresponding to an apparent molecular mass of 49 kDa. A sedimentation equilibrium centrifugation study of the active enzyme shows that the holoenzyme has a molecular mass of 98 kDa. Form A2 may be separated into two subunits of molecular mass of 64 kDa and 34 kDa, respectively. Thus, form A2 represents the holoenzyme with a true molecular mass of 98 kDa. Amino acid compositions and N-terminal amino acid sequences of the A2 protein and these subunits are consistent with a heterodimeric holoenzyme. The relationship between the conformational changes detected in this study and a three-state scheme proposed on the basis of EPR spectroscopic studies of the metal-containing cofactors present in the enzyme is also discussed.

Amino Acids↗
PubMed1987

Subunit interactions in the first component of complement, C1.

Interactions between C1q and other subunits of C1 were analyzed by sucrose gradient ultracentrifugation. A zone of dilute, radioiodine labelled C1q was sedimented through uniform concentrations of either C1r2C1s2, C1r2, C1r2 or C1s(2). The dissociation constants were found to be 3 x 10(-9) M and 6 x 10(-9) M for C1r2C1s2 and C1r2 binding respectively. Hill coefficients of 1 indicated no cooperativity in these bindings. Positive cooperativity was found in binding of C1s to C1q. Dissociation constants of 2 x 10(-6) M and 5 x 10(-8) M were obtained form computer modelling of a two step binding mechanism. No interaction was detected between C1q and activated C1r2. The data indicate that most of the interactions between C1q and C1r2C1s2 originates from a strong binding to the C1r2 moiety of the zymogen complex. This interaction is lost upon activation of C1r2.

Binding Sites↗
PubMed1987

A 'molten globule'-like unfolding intermediate of a four domain protein, the Fc fragment of the IgG molecule.

The Fc fragment of human IgG1 can be trapped in a stable intermediate state during thermal denaturation. In this conformation the molecule is compact with a native-like secondary structure, however, the tertiary structure is perturbed as revealed by intrinsic fluorescence measurements, the near-UV CD spectra and by mapping of antigenic sites with monoclonal antibodies. Similar phenomena were recently described for a few globular proteins of small size, and termed 'the molten globule' state. Our observation is a unique example of this phenomenon for a four domain protein.

Antibodies, Monoclonal↗
PubMed1987

Quantitative analysis of the interaction between immune complex and C1q complement subcomponent. The role of interdomain interactions in rabbit IgG in binding of C1q to immune precipitates.

A novel method was developed for the analysis of the interaction of large multivalent ligands with surfaces (matrices) to analyse the binding of complement subcomponent C1q to immune precipitates. Our new evaluation method provides quantitative data characteristic of the C1q-immune-complex interaction and of the structure of the immune complex as well. To reveal the functional role of domain-domain interactions in the Fc part of IgG the binding of C1q to different anti-ovalbumin IgG-ovalbumin immune complexes was studied. Immune-complex precipitates composed of rabbit IgG in which the non-covalent or covalent bonds between the heavy chains had been eliminated were used. Non-covalent bonds were abolished by splitting off the CH3 domains, i.e. by using Facb fragments, and the covalent contact was broken by reduction and alkylation of the single inter-heavy-chain disulphide bond. The quantitative analysis of the binding curves provides a dissociation constant (K) of 200 nM for the interaction between C1q and immune precipitate formed from native IgG. Surprisingly, for immune precipitates composed of Facb fragments or IgG in which the inter-heavy-chain disulphide bond had been selectively reduced and alkylated, stronger binding (K = 30 nM) was observed. In this case, however, changes in the structure of the immune-complex matrix were also detected. These structural changes may account for the strengthening of the C1q-immune-complex interaction, which can be strongly influenced by the flexibility and the binding-site pattern of the immune-complex precipitates. These results suggest that domain-domain interactions in the Fc part of IgG affect the segmental mobility of IgG molecules and the spatial arrangement of the immune-complex matrix rather than the affinity of individual C1q-binding sites on IgG.

Animals↗
PubMed1986

Acute and chronic efficacy of low-dose nitroglycerin patches in stable angina pectoris.

In a single-blind placebo controlled study, acute and chronic efficacy of low-dose nitroglycerin patches (NTG 5 mg/day) was studied in 24 patients with stable angina pectoris. NTG patch effects were evaluated by means of the multistage treadmill exercise test. During the acute study one exercise test was carried out after the wash-out period, after placebo patch (5 hours after application) and NTG patch (5, 16, 20 and 24 hours after application), so that a 3 day wash-out period had preceded each exercise test. Afterwards, chronic NTG patch therapy was continued for three months. At the end of this period exercise tests were carried out, in three day intervals of therapy, 5, 16, 20 and 24 hours after therapy. Then, a 7 day placebo patch period was continued with one exercise test at the end, 5 hours after application. Statistical analysis was carried out by multivariate analysis of difference. Systolic and diastolic blood pressure at rest fell significantly only in the acute 5 hour measurement, with no change in the other periods. The NTG patch augmented significantly mainly all heart rate values during exercise test, with no change in resting values. Placebo, acute and chronic exercise tests did not show any significant difference. They showed a slight but significant placebo influence on the exercise test compared to the wash-out period, improving maximum walking time and time to the onset of angina pectoris but with worsening of maximum ST-depression.(ABSTRACT TRUNCATED AT 250 WORDS)

Administration, Cutaneous↗
PubMed1985

Conformation of human IgG subclasses in solution. Small-angle X-ray scattering and hydrodynamic studies.

The structure of six human myeloma proteins: IgG1(Bal), IgG2(Klu), IgG3(Bak), IgG3(Het), IgG4(Kov) and IgG4(Pol), was studied in solution using small-angle X-ray scattering and hydrodynamic methods. For IgG1(Bal) and IgG3(Het) the experimental data, including radius of gyration (Rg degree), radii of gyration of the cross-section (Rq1, Rq2), intrinsic viscosity [eta], sedimentation coefficient (S degree 20,w) and molecular mass, were interpreted in terms of structural models based on the Fab and Fc conformations, observed in crystal, by varying the relative positions of the Fab and Fc parts, i.e. their relative angles and distances. The values Rg degree = (6.00 +/- 0.05) nm, S degree 20,w = (6.81 +/- 0.10) S and [eta] = 0.0062 +/- 0.0005 cm3/mg obtained for IgG1(Bal) are compatible with a planar model in which the angle between the Fab arms is about 120 degrees. For IgG3(Het) the following data were obtained: Rg degree = (4.90 +/- 0.05) nm, S degree 20,w = (6.32 +/- 0.01) S and [eta] = (0.0065 +/- 0.0005) cm3/mg. The apparent contradiction between the higher molecular mass and lower Rg degree and S degree 20,w values for IgG3(Het) in comparison to IgG1(Bal) can be resolved by proposing a 'non-planar' (tetrahedral) molecular shape, in which the long hinge peptide is in a folded conformation and the two Fab and Fc parts are in a closely packed arrangement. In this model the angle between the two Fab arms is about 90 degrees, in the average position. The X-ray scattering and hydrodynamic behaviour of the IgG2 and IgG4 types of antibodies appeared to be similar to IgG1(Bal). The parameters of the two IgG3 proteins are similar while they are different to the others.

Amino Acids↗
PubMed1981

Kinetic behaviour and oligomeric state of 3-phosphoglyceroyl-D-glyceraldehyde-3-phosphate dehydrogenase.

The specific activity of pig muscle D-glyceraldehyde-3-phosphate dehydrogenase was found to be constant in the reverse reaction, with NADH and 1,3-diphosphoglycerate as substrates, over the enzyme concentration range 10(-8) to 10(-4) M. The molecular weight of the covalent intermediate of the enzyme, 3-phosphoglyceroyl-glyceraldehyde-3-phosphate dehydrogenase, as measured by sedimentation techniques, proved constant (145 000 +/- 6 000) between 3 x 10(-5) M enzyme concentration. Likewise, no change in the apparent molecular weight was observed by gel-chromatography even at 2 x 10(-8) M enzyme concentration. The data indicate that the enzyme functions in its tetrameric form.

Animals↗
PubMed1980

L-alanine dehydrogenase from Thermus thermophilus.

A heat-stable L-alanine dehydrogenase was isolated and purified from the extremely thermophilic microorganism, Thermus thermophilus, by affinity chromatography. The enzyme has a molecular weight of 290 000, as determined by the sedimentation equilibrium method, and is composed of six subunits of identical molecular weight as concluded from sodium dodecyl sulphate gel electrophoresis. The enzyme has been characterized in terms of pH- and substrate concentration-dependence of activity, substrate specificity, inhibition by D-alanine and D-cysteine and amino acid composition. The parameters obtained are very similar to those reported for L-alanine dehydrogenase from the mesophilic microorganism, Bacillus subtilis (Yoshida, A. and Freese, E. (1965) Biochim. Biophys. Acta 96, 248--262). The thermal stability of the T. thermophilus enzyme is much greater than that of the B. subtilis enzyme. Activation free energy (delta G), activation enthalpy (delta H) and activation entropy (delta S) values were determined for both the alanine deamination and for the heat inactivation reactions of the thermophilic and mesophilic enzymes. The values obtained for the catalytic reaction were practically equal. However, the two enzymes differed significantly in these parameters determined for the enzyme inactivation, which indicates that the factors ensuring the thermoresistance of the enzyme from T. thermophilus do not affect enzyme activity.

Alanine Dehydrogenase↗
PubMed1980

Substrate-induced dissociation of glycerol-3-phosphate dehydrogenase and its complex formation with fructose-bisphosphate aldolase.

A threefold decrease in specific activity of glycerol-3-phosphate dehydrogenase was found on going from 800 nM to 10 nM enzyme concentration. According to ultracentrifugal analyses the dimeric glycerol-3-phosphate dehydrogenase (molecular weight 78,000) dissociates into monomers in the equilibrium mixture of its substrates and products. The concentration-dependent decrease in the specific activity is interpreted as a consequence of subunit dissociation and the estimated dissociation constants are 0.7 micro M and 3.5 micro M at 38 degrees C and 20 degrees C respectively. According to active-enzyme-band centrifugation experiments and kinetic analysis aldolase forms a complex with glycerol-3-phosphate dehydrogenase and this complex formation influences the specific activity of the dehydrogenase. The interaction between glycerol-3-phosphate dehydrogenase and aldolase can provide a regulatory mechanism at the branching point of glycolytic and lipid metabolic pathways.

Animals↗