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Biomedical subjects

S Lakatos

Publications and source records attributed to S Lakatos.

At least 37 records · Page 2Linked to original sources
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↗
PubMedDate not supplied

[Ultrastructural changes in the gastric mucosa in chronic gastritis in children].

Studying a series of 30 children with chronic gastritis (diagnosed by optic fiber gastroscopy and by mucosal biopsy), authors have founded important changes of the superficial mucosa and gastric glands. The histologic changes could explain the well-known functional alterations in chronic gastritis. They discussed also a possible immuno-pathogenic mechanism for these mucosal ultrastructural changes.

Adolescent↗