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L K Hansen

Publications and source records attributed to L K Hansen.

At least 55 records · Page 3Linked to original sources
PubMed1995

Crystallization and preliminary X-ray crystallographic studies of native elastase from North Atlantic salmon (Salmo salar).

Crystals of elastase from North Atlantic salmon have been grown from 2-methyl-2,4-pentanediol by the hanging-drop vapour-diffusion method at room temperature. They grow to dimensions of 0.7 x 0.4 x 0.3 mm in three weeks. The crystals belong to the tetragonal space group P4(1)2(1)2 or P4(3)2(1)2 with cell dimensions a = b = 68.0 A and c = 84.0 A. There are eight molecules in the unit cell. The crystals diffract to at least 1.6 A resolution and are suitable for a high-resolution crystal structure determination.

Journal Article↗
PubMed1995

[Ataxia telangiectasia].

Ataxia telangiectasia is a genetically determined multi-system disorder in which senile skin changes are at an early stage. The patients have progressive neurological disability, cellular and humoral immunodeficiencies and increased cancer incidence. Heterozygous carriers of the gene, estimated to comprise about 1% of the general population, have an increased risk of cancer. We have initiated an identification of a cohort of patients and their relatives in order to evaluate their cancer risk.

Adolescent↗
PubMed1995

Initial evaluation of children with heart murmurs by the non-specialized paediatrician.

UNLABELLED: To analyse the ability of the non-specialized paediatrician to evaluate children with a heart murmur and the consequences of this evaluation for the need of further investigations, we undertook a prospective and consecutive study of 100 children, referred for initial evaluation of a heart murmur. Except for 1 child with a slight peripheral pulmonary artery stenosis, 53% of the children were correctly diagnosed as having no heart disease. In a project design where 47% of the children were referred for an echocardiographic study, no clinically significant heart disease was missed. CONCLUSION: Clinical evaluation without laboratory tests performed by paediatricians without any special training in cardiology could correctly acquit 50% of the children of heart disease, with no need for further investigation.

Adolescent↗
PubMed1995

Kawasaki disease associated with parvovirus B19 infection.

UNLABELLED: In a 9-week-old boy with Kawasaki disease an active parvovirus B19 infection was diagnosed serologically. CONCLUSION: This case supports the hypothesis of an aetiological relationship between parvovirus B19 infection and Kawasaki disease.

Antibodies, Viral↗
PubMed1995

Comparative molecular dynamics simulation studies of salmon and bovine trypsins in aqueous solution.

The flexibility and conformational behaviour of salmon and bovine trypsins were modelled with a 300 ps molecular dynamics simulation in aqueous solution. Trajectories from both trypsins were analysed to eventually detect differences in mobility that could explain observed variations in stability and activity. The simulations were performed at 300 K with all the acidic groups deprotonated and the basic groups protonated. The radius of gyration, the overall r.m.s. deviation from the starting structure as a function of time, together with the r.m.s. deviation from the starting structures as a function of residue number, demonstrated that the simulations were stable and representative of the X-ray structures of both enzymes. Isotropic Debye-Waller factors were calculated from the fluctuations for main-chain atoms and were in good agreement with experimental values. The overall dynamic properties of the two enzymes were similar. Based on the present 300 ps molecular dynamics simulation, it cannot be concluded that either of the two enzymes is more 'flexible' than the other. However, there are clearly differences in mobility on a more detailed level and for particular regions.

Amino Acid Sequence↗
PubMed1995

Diagnostic value of chest radiography and electrocardiography in the evaluation of asymptomatic children with a cardiac murmur.

We investigated the diagnostic value of the chest radiograph and ECG in the evaluation of whether asymptomatic children with a cardiac murmur had a heart disease as defined by echocardiography. One hundred children aged 1 month to 15 years (median 30.1 months) were included. After physical examination, a tentative diagnosis was made: 53 children had no heart disease, 24 had a probable heart disease and 23 children were thought to have heart disease on the basis of clinical assessment alone. After information from chest radiography and electrocardiography was obtained, the diagnoses were re-evaluated. This resulted in a change of the tentative diagnosis in three children. However, the diagnosis in relation to the definite diagnosis by colour Doppler echocardiography was not changed to the correct diagnosis in any of these cases. In 24 cases, radiography suggested the presence of heart disease; however, only 10 of these had heart abnormalities on the colour Doppler echocardiogram (CDE). Three children had an abnormal ECG; all of these had abnormalities on the CDE, but they were already diagnosed as having heart disease by physical examination. We conclude that chest radiography and electrocardiography is of no help in the discrimination between heart disease and no heart disease in asymptomatic children referred for a cardiac murmur.

Adolescent↗
PubMed1994

Extracellular matrix controls tubulin monomer levels in hepatocytes by regulating protein turnover.

Cells have evolved an autoregulatory mechanism to dampen variations in the concentration of tubulin monomer that is available to polymerize into microtubules (MTs), a process that is known as tubulin autoregulation. However, thermodynamic analysis of MT polymerization predicts that the concentration of free tubulin monomer must vary if MTs are to remain stable under different mechanical loads that result from changes in cell adhesion to the extracellular matrix (ECM). To determine how these seemingly contradictory regulatory mechanisms coexist in cells, we measured changes in the masses of tubulin monomer and polymer that resulted from altering cell-ECM contacts. Primary rat hepatocytes were cultured in chemically defined medium on bacteriological petri dishes that were precoated with different densities of laminin (LM). Increasing the LM density from low to high (1-1000 ng/cm2), promoted cell spreading (average projected cell area increased from 1200 to 6000 microns2) and resulted in formation of a greatly extended MT network. Nevertheless, the steady-state mass of tubulin polymer was similar at 48 h, regardless of cell shape or ECM density. In contrast, round hepatocytes on low LM contained a threefold higher mass of tubulin monomer when compared with spread cells on high LM. Furthermore, similar results were obtained whether LM, fibronectin, or type I collagen were used for cell attachment. Tubulin autoregulation appeared to function normally in these cells because tubulin mRNA levels and protein synthetic rates were greatly depressed in round cells that contained the highest level of free tubulin monomer. However, the rate of tubulin protein degradation slowed, causing the tubulin half-life to increase from approximately 24 to 55 h as the LM density was lowered from high to low and cell rounding was promoted. These results indicate that the set-point for the tubulin monomer mass in hepatocytes can be regulated by altering the density of ECM contacts and changing cell shape. This finding is consistent with a mechanism of MT regulation in which the ECM stabilizes MTs by both accepting transfer of mechanical loads and altering tubulin degradation in cells that continue to autoregulate tubulin synthesis.

Animals↗
PubMed1994

Integrin binding and cell spreading on extracellular matrix act at different points in the cell cycle to promote hepatocyte growth.

This study was undertaken to determine the importance of integrin binding and cell shape changes in the control of cell-cycle progression by extracellular matrix (ECM). Primary rat hepatocytes were cultured on ECM-coated dishes in serum-free medium with saturating amounts of growth factors (epidermal growth factor and insulin). Integrin binding and cell spreading were promoted in parallel by plating cells on dishes coated with fibronectin (FN). Integrin binding was separated from cell shape changes by culturing cells on dishes coated with a synthetic arg-gly-asp (RGD)-peptide that acts as an integrin ligand but does not support hepatocyte extension. Expression of early (junB) and late (ras) growth response genes and DNA synthesis were measured to determine whether these substrata induce G0-synchronized hepatocytes to reenter the growth cycle. Cells plated on FN exhibited transient increases in junB and ras gene expression (within 2 and 8 h after plating, respectively) and synchronous entry into S phase. Induction of junB and ras was observed over a similar time course in cells on RGD-coated dishes, however, these round cells did not enter S phase. The possibility that round cells on RGD were blocked in mid to late G1 was confirmed by the finding that when trypsinized and replated onto FN-coated dishes after 30 h of culture, they required a similar time (12-15 h) to reenter S phase as cells that had been spread and allowed to progress through G1 on FN. We have previously shown that hepatocytes remain viable and maintain high levels of liver-specific functions when cultured on these RGD-coated dishes. Thus, these results suggest that ECM acts at two different points in the cell cycle to regulate hepatocyte growth: first, by activating the G0/G1 transition via integrin binding and second, by promoting the G1/S phase transition and switching off the default differentiation program through mechanisms related to cell spreading.

Amino Acid Sequence↗
PubMed1993

[Trichothiodystrophy. Hair examination as a diagnostic tool].

Trichothiodystrophy is a neuroectodermal syndrome with features of a specific hair dysplasia associated with disorders in organs derived from ectoderm and neuroectoderm. The key finding is brittle hair with low sulfur content. Polarizing microscopy shows alternating dark and light bands with trichoscisis and absent or defective cuticle. Patients with trichothiodystrophy have short, sparse, dry and easily broken hair. Growth retardation and mental retardation are almost obligatory findings. The skin and the nails are very often affected; other neuroectodermal disorders are associated, but none is a constant feature. The disease is transmitted as an autosomal recessive trait.

Child↗
PubMed1993

The crystal structure of tris-inhibited phospholipase C from Bacillus cereus at 1.9 A resolution. The nature of the metal ion in site 2.

We report here the crystal structure of the complex formed between phospholipase C (PLC) from Bacillus cereus and the widely used biochemical buffer tris (hydroxymethyl)-methylamine (Tris). The structure has been determined at 1.9 A resolution and refined to R = 20.3%. Tris has metal-binding properties, especially to Zn2+, and has been reported to reduce the activity of PLC. The amine nitrogen atom in Tris is co-ordinated to one of the three Zn2+ ions in the active site of the enzyme, thus confirming its chelating properties and the involvement of the metal ions in the catalytic process. The occupancy of the Zn2+ ion in site 2 in native PLC is 0.6 which could imply the presence of Ca2+ rather than Zn2+. The fact that Tris binds to this metal ion, the nature of the site 2 co-ordination shell and comparison with several homologous Zn-metalloenzymes indicate that PLC is a 3-Zn metalloenzyme. This study is one of a series which explores the active site of PLC by complexing the enzyme with inhibitors and substrate analogues.

Bacillus cereus↗
PubMed1993

A quantitative study of pruning by optimal brain damage.

The optimal brain damage (OBD) scheme of Le Cun, Denker and Solla for pruning of feedforward networks has been implemented and applied to the contiguity classification problem. It is shown that OBD improves the learning curve (the test error as a function of the number of examples). By inspecting the architectures obtained through pruning, it is found that the networks with less parameters have the smallest test error in agreement with "Ockhams Razor". Based on this, we propose a heuristic which selects the smallest successful architecture among a group of pruned networks and we show that it leads to very efficient optimization of the architecture. The validity of the approximations involved in OBD are discussed and it is found that they are surprisingly accurate for the problem studied.

Animals↗
PubMed1992

Crystal structures of phosphate, iodide and iodate-inhibited phospholipase C from Bacillus cereus and structural investigations of the binding of reaction products and a substrate analogue.

The crystal structure of the complex formed between phospholipase C (PLC) from Bacillus cereus and inorganic phosphate (Pi), which is an inhibitor, has been determined and refined to 2.1 A resolution. The final R-factor is 19.7%. We have also studied the binding of two other inhibitors, iodide and iodate, to PLC. X-ray data for these two complexes were collected to 2.8 A resolution during the search for heavy-atom derivatives. A series of screening experiments where PLC crystals have been treated with several reaction products and a substrate analogue were carried out to clarify the question of substrate binding. The results have so far been ambiguous but are discussed briefly. Phosphate and iodate are both found to bind to the three metal ions in the protein molecule, suggesting that these ions are involved directly in the catalytic process and thereby identifying the active site. PLC also binds nine iodide ions, eight of which are on the surface of the molecule and of lower occupancy. The ninth blocks the entrance to the active site cleft and is of higher occupancy. Altogether, these results suggest that the substrate, a phospholipid, is associated directly with the metal ions during catalysis.

Bacillus cereus↗
PubMed1991

Crystallization and preliminary X-ray crystallographic studies of CO-hemoglobin from the North Atlantic salmon (Salmo salar).

Purification of hemoglobin from North Atlantic salmon (Salmo salar) gave three different types. The CO-complexes of types I and III have been crystallized by the batch method at 4 degrees C from solutions 18% (w/v) in polyethylene glycol 2000, 50 mg/ml in hemoglobin and 0.05 M in phosphate buffer (pH 8.3). Orthorhombic crystals, space group P2(1)2(1)2(1), were obtained for both, with cell dimensions a = 53.9 A, b = 80.4 A, c = 132.4 A, and a = 58.7 A, b = 95.0 A, c = 107.4 A, for types I and III, respectively.

Animals↗
PubMed1991

Differential regulation of HSC70, HSP70, HSP90 alpha, and HSP90 beta mRNA expression by mitogen activation and heat shock in human lymphocytes.

A subset of heat shock proteins, HSP90 alpha, HSP90 beta, and a member of the HSP70 family, HSC70, shows enhanced synthesis following mitogenic activation as well as heat shock in human peripheral blood mononuclear cells. In this study, we have examined expression of mRNA for these proteins, including the major 70-kDa heat shock protein, HSP70, in mononuclear cells following either heat shock or mitogenic activation with phytohemagglutinin (PHA), ionomycin, and the phorbol ester, tetradecanoyl phorbol acetate. The results demonstrate that the kinetics of mRNA expression of these four genes generally parallel the kinetics of enhanced protein synthesis seen following either heat shock or mitogen activation and provide clear evidence that mitogen-induced synthesis of HSC70 and HSP90 is due to increased mRNA levels and not simply to enhanced translation of preexisting mRNA. Although most previous studies have focused on cell cycle regulation of HSP70 mRNA, we found that HSP70 mRNA was only slightly and transiently induced by PHA activation, while HSC70 is the predominant 70-kDa heat shock protein homologue induced by mitogens. Similarly, HSP90 alpha appears more inducible by heat shock than mitogens while the opposite is true for HSP90 beta. These results suggest that, although HSP70 and HSC70 have been shown to contain similar promoter regions, additional regulatory mechanisms which result in differential expression to a given stimulus must exist. They clearly demonstrate that human lymphocytes are an important model system for determining mechanisms for regulation of heat shock protein synthesis in unstressed cells. Finally, based on kinetics of mRNA expression, the results are consistent with the hypothesis that HSC70 and HSP90 gene expression are driven by an IL-2/IL-2 receptor-dependent pathway in human T cells.

Cells, Cultured↗