Search PubMed⌕ Search

Biomedical subjects

B Sjöberg

Publications and source records attributed to B Sjöberg.

At least 19 recordsLinked to original sources
PubMed1992

Structure of RecA-DNA complexes studied by combination of linear dichroism and small-angle neutron scattering measurements on flow-oriented samples.

By combining anisotropy of small-angle neutron scattering (SANS) and optical anisotropy (linear dichroism, l.d.) on flow-oriented RecA-DNA complexes, the average DNA-base orientation has been determined in RecA complexes with double-stranded (ds) as well as single-stranded (ss) DNA. From the anisotropy of the two-dimensional SANS intensity representation, the second moment orientation function S is obtained. Knowledge of S is crucial for the interpretation of l.d. spectra in terms of orientation of the DNA bases and the aromatic amino acid residues. The DNA-base planes are essentially perpendicular to the fibre axis of the complex between RecA and dsDNA in the presence of cofactor ATP gamma S. A somewhat tilted base geometry is found for the RecA-ATP gamma S complexes with single-stranded poly(dT) and poly(d epsilon A). This behaviour contrasts the RecA-ssDNA complex formed without cofactor which displays a poor orientation of the bases. Well-ordered bases in the ssDNA-RecA complex is possibly reflecting the role of RecA in preparing a nucleotide strand for base-pairing in the search-for-homology process. While the central SANS intensity is essentially independent of the pitch of the helical complex, a secondary intensity maximum, which becomes focused upon flow orientation, is found to be a sensitive measure of the pitch. The pitch values for the complexes compare well with cryo-electron microscopy results but are slightly larger than those seen for uranyl-stained samples.

Adenosine Triphosphate↗
PubMed1992

Temperature dependence of the kinetics of the urea-induced dissociation of human plasma alpha 2-macroglobulin into half-molecules. A minimum rate at 15 degrees C indicates hydrophobic interaction between the subunits.

The kinetics of the urea-induced dissociation of human plasma alpha 2-macroglobulin to half-molecules has been studied as a function of temperature by using small-angle scattering of X-rays and neutrons. The most striking result of the present investigation is that there is a minimum in reaction rate at about 15 degrees C, and that the rate increases when the temperature is lowered, or raised, from that value. By analyzing the first-order rate constants in terms of transition-state theory it was found that the dissociation is associated with a large and positive change in heat capacity between the activated complex and native alpha 2-macroglobulin (delta CP is in the range 5 to 6 kJ mol-1 K-1). In analogy with pure thermodynamic investigations, where a large change in heat capacity normally is interpreted as a melting of hydrophobic interaction, we therefore propose that hydrophobic interaction is involved in the so-called non-covalent interactions between the subunits of alpha 2-macroglobulin. As a result of the present investigation, it also follows that the free energy of activation delta G has a maximum at about 32 degrees C, whereas the enthalpy of activation delta H and the entropy of activation delta S are zero at about 15 degrees C and 32 degrees C, respectively. These temperatures are slightly dependent upon the concentration of urea and upon whether the reaction is run in a 1H or a 2H medium. Furthermore, from the kinetic point of view, at low temperature the reaction can be characterized as enthalpy driven, whereas at high temperature, it can be characterized as entropy driven.

Humans↗
PubMed1978

Trisodium phosphonoformate, a new antiviral compound.

Trisodium phosphonoformate selectively inhibits cell-free DNA polymerase activity induced by herpesvirus. The new inhibitor has an antiviral effect on herpes simplex virus types 1 and 2, pseudorables virus, and infectious bovine rhinotracheitis virus in cell culture. It has a good therapeutic activity against cutaneous herpes simplex virus infection in guinea pigs.

Animals↗
PubMed1978

A small angle X-ray study of the elongation factor complex Tu . GDP from Escherichia coli.

The protein elongation factor complex Tu. GDP from Escherichia coli was investigated in the presence of 0.01 mM GDP using the small-angle X-ray method. The overall shape and the molecular parameters of the Tu . GDP complex were determined using a least-squares method where the experimental data were used directly without desmearing. The best fit to the experimental data was obtained assuming the molecule to be an ellipsoid of revolution with the semiaxes A = B = 4.08 nm, and C = 1.18nm. Determination of the molecular weight gave the result Mr = 46 000, which corresponds to a water content equal to 26% (by weight).

Bacterial Proteins↗
PubMed1978

Small-angle X-ray titration of the complex formed between the ribosomal protein S4 and its 16S binding site, S4-RNA: a central core in the 30S subunit.

X-ray scattering titrations at 21 degree C and in ribosomal reconstitution buffer indicate that the S4-RNA and the protein S4 from a 1:1 complex with a stability constant, log K approximately 6.5. When the complex forms, there is only a limited change in the scattering curve indicating that S4-RNA essentially retains its conformation during the complex formation. The increase in the gyration radius as a result of the complex formation, delta R = 4 +/- 3 A, as well as the experimental scattering curve of the complex can be explained by models where the protein S4 is supposed to interact with the periphery of the S4-RNA.

Binding Sites↗
PubMed1976

Molecular model for 5-S RNA. A small-angle x-ray scattering study of native, denatured and aggregated 5-S RNA from Escherichia coli ribosomes.

A tertiary structural model is suggested for Escherichia coli 5-S RNA that consists of one large and two small double helices arranged in the form of the letter Y. This model is consistent with the small-angle X-ray scattering data of native 5-S RNA, measured in the angular range 20 less than or equal to 140 mrad. The radium of gyration is 3.61 +- 0.1 Nm. Denatured 5-S RNA yields a much lower radius of gyration, 2.7 nm, which might indicate that during denaturation one minor double-helical arm of the Y-shaped structure partially collapses into single-stranded areas. At high concentrations (60 mg/ml) of 5-S RNA, the X-ray scattering data indicate that 5-S RNA is aggregated.

Base Sequence↗
PubMed1975

The effect of ATP and related compounds on spontaneous mechanical activity in the rat portal vein.

The effects of ATP, ADP, AMP and adenosine were studied on the spontaneous mechanical activity of the rat portal vein. 2It was found that STP and ADP, in concentrations higher than 300 mug M, caused a transient tetanus, followed by inhibition, and at lower concentrations an increase in the frequency and amplitude of the spontaneous contractions. AMP and adeosine on the other hand, inhibited spontaneous activity, by reducing the amplitude of contractions and increasing their frequency. The effects were dose-dependent. ATP was found to be 2.2 times more potent than ADP, while AMP and adenosine were equipotent. Weak inhibitory effects were obtained with GMP, guanosine and adenine, while GTP, 3K-cyclic AMP and guanine had no effect. ATP and ADP increased the K-contracture, while AMP and adenosine relaxed it. The effects of ATP were augmented in Mg-free solutions and partially inhibited in Mg-high solutions in the normally polarized muscle, while Mg had no influence on the ATP-induced contraction in the depolarized muscle. Theophylline potentiated the inhibitory response to AMP and adenosine. Adrenergic and cholinergic blockers had no influence on the response to ATP, ADP, AMP or adenosine. It is suggested that the effects of ATP and ADP are linked with Ca++ movements across the membrane, while AMP and adenosine might stimulate intracellular metabolism causing increased intracellular Cs-++ binding.

Acetylcholine↗
PubMed1975

Bacampicillin: a new orally well-absorbed derivative of ampicillin.

Bacampicillin (proposed international nonproprietary name), 1'-ethoxycarbonyloxyethyl 6-(d-alpha-aminophenylacetamido)penicillanate, is a new orally well-absorbed penicillin, highly active in vivo due to rapid transformation into ampicillin. The compound is stable in vitro at gastric pH and hydrolyzed slowly to ampicillin at neutral pH but very rapidly in the presence of biological fluids, e.g., tissue homogenates or serum. In vivo the transformation into ampicillin is so rapid that no unchanged compound could be detected in the blood after oral administration of bacampicillin to rats, dogs, and humans. On oral administration to mice, rats, and dogs, bacampicillin was found to be better absorbed than ampicillin, giving higher and earlier peak blood levels of ampicillin. The bioavailability of bacampicillin in rats and dogs was three to four times higher than that of an equimolar amount of ampicillin. On oral administration to rats, bacampicillin was found to give higher levels of ampicillin in organs such as the kidney, liver, and spleen than ampicillin itself. In "tissue cages" in rats, higher transudate levels of antibiotic were found after oral administration of bacampicillin than after ampicillin. On oral treatment of experimentally infected mice, bacampicillin was found to be more active than ampicillin.

Ampicillin↗