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Biomedical subjects

L K Hansen

Publications and source records attributed to L K Hansen.

15 recordsLinked to original sources
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↗
PubMed1990

Crystallization and preliminary X-ray crystallographic studies of benzamidine-inhibited trypsin from the North Atlantic salmon (Salmo salar).

Crystals of benzamidine-inhibited trypsin from the North Atlantic salmon (Salmo salar) have been grown from ammonium sulphate solution at pH 5.0. Two crystal forms suitable for X-ray structure analysis, obtained from a hanging-drop experiment, have been characterized. Both belong to space-group P22(1)2(1) with cell dimensions a = 39.2 A, b = 62.4 A, c = 84.6 A and a = 31.4 A, b = 74.8 A, c = 83.5 A, for forms I and II, respectively. Intensity data to 1.82 A have been collected for crystal form I on a CAD4 diffractometer, and initial phases have been obtained by molecular replacement methods. The conventional R-factor after two rounds of model building and subsequent refinement is 0.25 for data between 6.0 and 2.0 A. So far no water molecules have been included in the model.

Amidines↗
PubMed1990

The relationship of white blood cell count to other cardiovascular risk factors.

Baseline data for the 12,866 men from the Multiple Risk Factor Intervention Trial was used to study factors related to white blood cell (WBC) count. White blood cell count was significantly higher in smokers (7853 cells/mm3) and ex-smokers (7091 cells/mm3) who stopped smoking less than one year before than in ex-smokers who stopped more than one year before (6255 cells/mm3) and those who never smoked (6094 cells/mm3). In current cigarette smokers, white blood cell count was significantly related to number of cigarettes smoked, degree of inhalation, and duration of smoking (p less than 0.001 for each). In addition, white blood cell count was higher in non-cigarette smokers who smoked pipes, cigars, or cigarillos than among men who did not smoke tobacco (p less than 0.001). White blood cell count was lower in blacks (by 877 cells/mm3) and Orientals (by 634 cells/mm3) than in whites. Leukocyte count also showed a strong inverse association with high density lipoprotein (HDL)-cholesterol, a positive association with triglycerides independent of cigarette use, and a positive association with low density lipoprotein (LDL)-cholesterol in smokers only. Leukocyte counts were inversely related to total family income and alcohol consumption. We conclude that elevated leukocyte count is independently associated with other risk factors for coronary heart disease (CHD) such as amount and duration of smoking as well as an atherogenic profile, and these relationships should be considered when using white blood cell count as a predictor of coronary heart disease.

Adult↗
PubMed1989

High-resolution (1.5 A) crystal structure of phospholipase C from Bacillus cereus.

Both the phosphatidylinositol-hydrolysing and the phosphatidylcholine-hydrolysing phospholipases C have been implicated in the generation of second messengers in mammalian cells. The phosphatidylcholine-hydrolysing phospholipase C (PLC) from Bacillus cereus, a monomeric protein containing 245 amino-acid residues, is similar to some of the corresponding mammalian proteins. This, together with the fact that the bacterial enzyme can mimic the action of mammalian PLC in causing, for example, enhanced prostaglandin biosynthesis, suggests that B. cereus PLC can be used as a model for the hitherto poorly characterized mammalian PLCs. We report here the three-dimensional structure of B. cereus PLC at 1.5 A resolution. The enzyme is an all-helix protein belonging to a novel structural class and contains, at least in the crystalline state, three Zn2+ in the active site. We also present preliminary results from a study at 1.9 A resolution of the complex between PLC and inorganic phosphate (Pi) which indicate that the substrate binds directly to the metal ions.

Bacillus cereus↗
PubMed1989

Bilateral female pelvic actinomycosis.

A case of bilateral actinomycotic salpingitis is described. The woman used an IUD and the course of the disease was protracted. Later, Actinomyces israelii was coincidentally identified from vaginal cultures. Attention is drawn to the need for distinction between the presence of Actinomyces israelii and actinomycosis.

Actinomycosis↗
PubMedDate not supplied

Preparation, analysis, and anticholinesterase properties of O,O-dimethyl phosphorothioate isomerides.

Previous studies have shown that impurities in commercial organophosphorus insecticides induce a variety of toxicological manifestations. Few studies have contrasted common impurity types and their comparative chemical and biochemical properties. In this study, five O,O-dimethyl phosphorothioate compounds were converted to their corresponding O,S-dimethyl phosphorothioates (isomerides) by a stepwise dealkylation-alkylation process (yields 58-76%). The O,S-isomerides and parent material were characterized by reverse-phase high-performance liquid chromatography (RPHPLC) and phosphorus (31P) nuclear magnetic resonance (NMR) spectroscopy. Methanol-water mixtures were found to adequately separate isomeride from parent structure with the isomeride eluting first. In general, the O,S-isomerides were found to be shifted about 40 ppm upfield relative to the O,O material. Isomerides were also determined to be significantly more potent as anticholinesterases (rat brain), with ki values approximating 1000-fold those of the parent material.

Animals↗