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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↗
PubMed1991

Kinetics of the urea-induced dissociation of human plasma alpha 2-macroglobulin as measured by small-angle neutron scattering.

The kinetics of the urea-induced dissociation of human plasma alpha 2-macroglobulin into two half-molecular fragments was investigated at 21.0 degrees C by using small-angle neutron scattering. The relative change in molecular mass that occurs upon dissociation was monitored by recording the forward scattering of neutrons as a function of time. All these kinetic data can be explained by a reaction that is first-order with respect to the concentration of undissociated alpha 2-macroglobulin. The velocity constant is a function of urea concentration and it varies within wide limits. For instance, the half-life of the reaction at the lowest concentration of [2H]urea studied (2.70 M) is 328 h, whereas the same value at the highest concentration of [2H]urea (6.24 M) is only 8 min. Measurements were made both with [1H]urea in 1H2O and with [2H]urea in 99% 2H2O, and it was found that there is a pronounced kinetic isotope effect, i.e. the dissociation is 4 times faster in the 1H-containing medium as compared with the 2H-containing medium at the same molar concentration of urea. From the angular dependence of the neutron scattering it can be concluded that the dissociation is associated with a drastic change in structure. This is directly shown by the radius of gyration, which increases from about 7.4 nm immediately after the addition of urea up to about 9.4 nm when the protein is fully dissociated. A structural analysis shows that the scattering curve of urea-dissociated alpha 2-macroglobulin can best be explained by that of a Gaussian coil with a radius of gyration equal to 9.44 nm. These data indicate that the so-called non-covalent interaction of alpha 2-macroglobulin probably is more complicated than just a pure hydrophobic interaction. Finally, it is also shown that the dissociation is accompanied by a loss in trypsin-binding activity, which is directly related to the fraction of dissociated protein.

Animals↗
PubMed1990

Structure of a RecA-DNA complex from linear dichroism and small-angle neutron-scattering in flow-oriented solution.

Small-angle neutron-scattering (SANS) and ultraviolet linear dichroism (l.d.) were measured on identical samples of a RecA-double-stranded (ds) DNA complex, including cofactor adenosine 5'-O-thiotriphosphate, which were aligned by flow in two equivalent Couette devices made of niobium and silica, transparent to neutrons and to ultraviolet light, respectively. The SANS anisotropy indicates a modest orientation of the RecA-dsDNA fiber with the helix axis parallel to the flow field. By correlation with the corresponding l.d. of the DNA at the same orientation conditions, it is inferred that the DNA bases have a local orientation that is approximately perpendicular to the helix axis. By comparison with the worse orientation in single-stranded DNA-RecA, this conclusion suggests that the dsDNA in its complex with RecA is not strand separated, and may be accommodated as an essentially unperturbed, straight double helix running along the RecA polymer fiber. The SANS anisotropy is also found to support the assignment of a subsidiary intensity maximum as originating from the pitch of a helical fiber.

Animals↗
PubMed1990

The H(+)-induced dissociation of human plasma alpha 2-macroglobulin. An investigation using small-angle neutron scattering and test of trypsin binding activity.

The dissociation of the tetrameric alpha 2-macroglobulin molecule into two half-molecular fragments, which occurs at pH less than 4.5, has been investigated using the small-angle neutron scattering method, and test of trypsin binding activity. Best fit with the relative forward scattering of neutrons is obtained for a model where the dissociation of the protein is driven by the uptake of H+ on altogether four acid-base groups, one per monomeric subunit of alpha 2-macroglobulin. These groups are not (or only slightly) accessible in the native tetramer, but become exposed to the solvent after dissociation of the protein. The H(+)-binding constant obtained for these groups, after dissociation of the protein, log K1 in the range 4.2-4.5, suggests that they are most probably carboxylate groups. From the about 10% increase in the radius of gyration, which occurs when lowering the pH from 4.5 to 2.0, we can conclude that the dissociation is associated with a change in structure of the protein. Tests of trypsin binding show that there is also an irreversible loss in trypsin binding activity, which is directly related to the fraction of dissociated protein. Thus, at pH less than 4.5, there is a transition of alpha 2-macroglobulin which results simultaneously in dissociation, disorganisation of the conformation of the subunits and loss in activity.

Binding Sites↗
PubMed1990

Effect of combined treatment with phenylpropanolamine and estriol, compared with estriol treatment alone, in postmenopausal women with stress urinary incontinence.

Twenty-nine postmenopausal women with slight to severe stress urinary incontinence and estrogen deficiency symptoms in the urogenital tract were treated with estriol, p.o. 4 mg once daily, and either phenylpropanolamine (PPA), p.o. 50 mg twice daily, or placebo for periods of 6 weeks according to a randomized double-blind crossover schedule. At urodynamic recordings the maximum urethral closure pressure increased by 22% with combined treatment (p less than 0.001) and an additional effect of PPA to estriol was shown (p = 0.022). The pressure transmission ratio increased, by about 15%, with both treatments (p less than 0.07). The number of leakage episodes was reduced by 28% with combined treatment (p = 0.007), but not with estriol alone (p = 0.08). Both combined treatment and estriol alone reduced significantly (p less than 0.01) the urinary incontinence complaints. Twelve women (43%) preferred combined treatment, while 7 (25%) preferred estriol alone. In women with initially slight to very severe urine loss, combined treatment reduced also (p = 0.02) the amount of urine loss, measured at a standardized physical stress test. Signs of estrogen deficiency in vulva, vagina and urethra were reduced, 75% (p less than 0.001) or 65% (p = 0.001) with estriol given in combination with PPA or alone. Maturation index of both urethral and vaginal epithelium displayed significant changes. It is concluded that the combined treatment, PPA + estriol, by affecting both the muscular and mucosal factor of the urethra, is more effective than estriol alone for treatment of female stress urinary incontinence in the postmenopausal ages.

Double-Blind Method↗
PubMed1989

Molecular organization of human plasma alpha 2-macroglobulin and its trypsin complexes. A small-angle x-ray scattering investigation.

The molecular organization of human plasma alpha 2-macroglobulin (alpha 2M), and its 1:1 and 1:2 trypsin complexes, have been investigated using the small-angle x-ray scattering method. All the experimental data can be explained by the same basic model, consisting of three oblate-shaped domains arranged in a sandwich-like structure. Each of the larger peripheral domains consists of two parallel elliptic cylinders associated side-by-side, whereas the smaller central domain consists of just one elliptic cylinder. In the native molecule the three domains are separated by regions of low protein density. Upon trypsin binding the dimensions of the four peripheral cylinders remain unchanged, but their positioning in space is reorganized so that the whole molecule becomes more compact. The model thus offers a plausible explanation for the mechanism of inactivating of the protease by entrapping it between the two larger domains. By comparing the shape and dimensions of the total molecule with those determined for the half-molecular fragment, obtained after reducing the intersubunit disulfide bonds, we propose that the fragment consists of just one of the peripheral domains plus half of the central domain. Different projections of the model are consistent with the electron micrographs of alpha 2M given in the literature. The model can also explain many of the physical and chemical properties recorded for alpha 2M and its protease complexes.

Disulfides↗
PubMed1989

Solution structure of human plasma fibronectin as a function of NaCl concentration determined by small-angle X-ray scattering.

The structure of human plasma fibronectin in 50 mM Tris-HCl buffer, pH 7.4, containing varying concentrations of NaCl, has been investigated using the small-angle X-ray method. Below 0.3 M NaCl the overall structure of the molecule is disc-shaped; at 0 M NaCl the axial ratio of the disc is about 1:7 and between 0.1 M to 0.3 M it is slightly more asymmetric, with an axial ratio of 1:10. At about 0.3 M NaCl there is a reversible transition to a more open structure, and, from 0.3 M up to 1.1 M NaCl the small-angle X-ray data can be explained by models consisting of ensembles of flexible, non-overlapping, bead-chains generated by a Monte Carlo procedure. Within this concentration range there is a gradual increase in the stiffness of the chains, as well as a decrease in bead radius, which indicates that the molecule becomes more open when the NaCl concentration is increased. The transition to a more open structure is also demonstrated by the average radius of gyration which increases gradually from 8.26 nm at 0 M NaCl to 8.75 nm at physiological or near-physiological conditions, and up to 16.2 nm at 1.1 M NaCl.

Fibronectins↗
PubMed1987

Dodecylsulfate-induced dissociation of human alpha 2-macroglobulin. An investigation using small-angle neutron scattering and the equilibrium dialysis technique.

The dodecylsulfate-induced dissociation of the tetrameric alpha 2-macroglobulin molecule from human plasma has been investigated by the small-angle neutron scattering (SANS) method. The great advantage with the SANS method is that, by using deuterated dodecylsulfate, and contrast variation by changing the D2O/H2O ratio of the solvent, we can selectively study just the protein part, or the dodecylsulfate part, of the protein-dodecylsulfate complex. More than a thousandfold excess of dodecylsulfate (on a molar basis) is needed in order to dissociate alpha 2-macroglobulin to particles with, on average, half the original molecular mass. By combining the SANS data with results obtained by the equilibrium dialysis technique it follows that, under these circumstances, approximately one thousand dodecylsulfate molecules are associated per alpha 2-macroglobulin molecule. From the significant increase in the radius of gyration, which accompanies the dissociation process, we can conclude that the dissociation is associated with a drastic change in conformation of the protein molecule. From measurements where the dodecylsulfate part of the complex dominates the SANS signal we also get an indication that the dodecylsulfate is randomly distributed along the polypeptide chain, rather than being arranged in large clusters at certain regions of the protein molecule. By fitting the parameters of a binding model to the experimental data we obtain the result that most of the more than one thousand bound dodecylsulfate molecules, necessary for dissociation, are involved in the change in conformation, and the dissociation process is, in fact, driven by the binding of a very few extra dodecylsulfate molecules to the dissociation products. These data indicate that the dodecylsulfate-induced dissociation of alpha 2-macroglobulin is probably more complicated than just breaking, for instance, a hydrophobic interaction.

Dialysis↗
PubMed1987

Solution structure of human plasma fibronectin using small-angle X-ray and neutron scattering at physiological pH and ionic strength.

Human plasma fibronectin has been investigated at physiological pH and ionic strength, by using small-angle X-ray and neutron scattering techniques. The results indicate that the molecule is disc shaped with an axial ratio of about 1:10. In fact, an ellipsoid of revolution with semiaxes a = 1.44 nm and b = c = 13.8 nm is in agreement with the experimental scattering data, and can also fully explain the rather extreme hydrodynamic parameters reported for fibronectin. The X-ray data gave a radius of gyration of 8.9 nm and a molecular weight of 510,000, whereas the neutron data gave slightly larger values, 9.5 nm and 530,000, respectively. From the volume of the best fitting ellipsoid we obtain a degree of hydration of 0.61 g H2O/g protein (dry weight). Neutron data, recorded at different D2O concentrations in the solvent, gave a match point of 43% D2O, which indicates that approximately 80% of the hydrogens bound to oxygen and nitrogen are exchangeable.

Fibronectins↗
PubMed1986

Blood and tissue steroid levels and their interrelationship in men with pathological conditions of the reproductive organs.

We have investigated the interrelationship of the levels of 10 steroids in peripheral venous, spermatic arterial and spermatic venous blood, and in tissue specimens from the epididymis, vas deferens and testis from 8 patients who underwent orchidectomy for pathological conditions of the reproductive organs. The steroids analyzed by radioimmunoassay were: pregnenolone (5-P), dehydroepiandrosterone (DHEA), 17-hydroxyprogesterone (17-OH-P), androstenedione (A), testosterone (T), dihydrotestosterone (DHT) and the sulpho-conjugated forms (-S) of 5-P, DHEA, T and DHT. The quantitatively major steroids in peripheral venous blood were, in order of magnitude, DHEA-S, 5-P-S, DHT-S, T-S and T. No difference was observed between the levels of any of the steroids measured in peripheral venous and spermatic arterial blood. With the exception of DHEA-S and DHT-S, the levels of all steroids in spermatic venous blood were substantially higher than in peripheral venous blood (P less than 0.001). No correlation was found between steroid levels in spermatic venous and peripheral venous blood. Steroid concentrations in tissue from the epididymis, vas deferens and testis were markedly higher than in peripheral venous blood (P less than 0.01 to P less than 0.001), except for the levels of DHEA-S which were about equal in the various blood and tissue specimens. Tissue to blood ratios varied from approximately 2.0 to 500 according to the steroid in question. The peripheral blood levels of 5-P-S, DHEA-S and DHT-S were substantially higher than respective unconjugated steroid levels (P less than 0.001); the ratios (sulpho-conjugated to unconjugated) were approximately 17, 215 and 30, respectively.(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗
PubMed1986

Malate-aspartate and alpha-glycerophosphate shuttle enzyme levels in human skeletal muscle: methodological considerations and effect of endurance training.

The aim of the present study was to investigate whether the levels of the malate-aspartate and alpha-glycerophosphate shuttle enzymes in human skeletal muscle are affected by endurance training. The approach used was to compare six untrained and six endurance-trained subjects as well as through performing a longitudinal study of endurance training on eight untrained subjects. Biopsy samples were obtained from the lateral part of the quadriceps femoris muscle. The trained muscles were characterized by higher levels of oxidative enzymes (55%) as well as enhanced capillary supply (30%). In both the cross-sectional and longitudinal studies, the malate-aspartate shuttle enzyme levels were about 50% higher in the trained state (cytoplasmic malate dehydrogenase 36%, mitochondrial malate dehydrogenase 46%, cytoplasmic aspartate aminotransferase 52% and mitochondrial aspartate aminotransferase 48%). Contrary to this, the alpha-glycerophosphate shuttle enzyme levels did not differ significantly (cytoplasmic and mitochondrial glycerol-3-phosphate dehydrogenase: 10 and -4%, respectively). The activity ratios of the enzymes involved in respective shuttle did not differ significantly between the untrained and endurance-trained states. It is concluded that endurance training may induce increased levels of malate-aspartate shuttle enzymes in human skeletal muscle while the levels of the alpha-glycerophosphate shuttle enzymes are not affected. The study also includes results from several methodological experiments.

Adult↗
PubMed1985

Outcome of different treatment modalities in cervix carcinoma Stage IB and IIA. Observations in a well-defined Swedish population.

Stage IB or IIA carcinoma of the cervix in a nonselected series of 263 young (less than or equal to 40 years) women was managed with radiotherapy alone or in combination with radical surgery. When the tumor was detected in Stage IB, the 5-year survival rate was 81% in the radiotherapy group and 96% in the combined therapy group. The corresponding figures for Stage IIA were 74% and 66%, respectively. When lymph node metastases were present at operation, the 5-year survival rate was reduced. The reduction was relatively small in Stage IB, but was decreased from 83% to 27% in Stage IIA. The size of the tumor had prognostic impact on the survival rate. Residual tumor in the surgical specimens was likewise associated with poorer prognosis in Stage IIA. The prediagnostic duration of symptoms indicates that the longer the pretreatment time and higher the stage at diagnosis, the greater the likelihood of metastatic spread. Adenocarcinomas comprised 13% of the tumors in the series. Complications of treatment were few.

Adenocarcinoma↗
PubMed1985

Characterization of a half-molecular fragment obtained by reduction of human alpha 2-macroglobulin with dithiothreitol. A small-angle X-ray and neutron scattering investigation.

A half-molecular fragment of alpha 2-macroglobulin has been prepared by reducing and alkylating the inter-subunit disulfide bonds in the tetrameric alpha 2-macroglobulin molecule with 1 mM dithiothreitol (40 min) and 3 mM iodoacetamide (40 min). Further purification was made by gel chromatography and the homogeneous population of half-molecules has been characterized by the techniques of small-angle X-ray and neutron scattering. The radii of gyration found by the two methods are 57.0 and 58.0 A, respectively. The match point, obtained by neutron scattering from solutions with different H2O/D2O ratios, is at 43% D2O; the data are consistent with a particle having a higher scattering density at large distances from the particle centre. From the X-ray and neutron intensities scattered at zero angle, the specific volume was determined to be 0.73 cm3/g at +5 degrees C and the molecular weight to be 390,000; the latter value is associated with a relatively large error due to the uncertainty in the concentration determination. Shape analysis indicates that the best-fitting scattering-equivalent three-axial bodies are oblate shaped, with two of their axial dimensions about three to four times larger than the third one. From the volume of the best-fitting scattering-equivalent three-axial bodies, 0.72 X 10(6) A3, we obtain a water content equal to 0.38 g H2O/g protein (dry weight).

Dithiothreitol↗
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↗