Biomedical subjects
Publications and source records attributed to H Loos.
We report the first experimental results on a high-gain harmonic-generation (HGHG) free-electron laser (FEL) operating in the ultraviolet. An 800 nm seed from a Ti:sapphire laser has been used to produce saturated amplified radiation at the 266 nm third harmonic. The results confirm the predictions for HGHG FEL operation: stable central wavelength, narrow bandwidth, and small pulse-energy fluctuation.
Experimental results are presented from vacuum-ultraviolet free-electron laser (FEL) operating in the self-amplified spontaneous emission (SASE) mode. The generation of ultrashort radiation pulses became possible due to specific tailoring of the bunch charge distribution. A complete characterization of the linear and nonlinear modes of the SASE FEL operation was performed. At saturation the FEL produces ultrashort pulses (30-100 fs FWHM) with a peak radiation power in the GW level and with full transverse coherence. The wavelength was tuned in the range of 95-105 nm.
Glucose-fructose oxidoreductase (E.C. 1.1.99.-) from the ethanol-producing Gram-negative bacterium Zymomonas mobilis is a periplasmic, soluble enzyme that forms a homotetramer of 160 kDa with one NADP(H) cofactor per subunit that is tightly, but noncovalently, bound. The enzyme was crystallized by the hanging drop vapor diffusion method using sodium citrate as precipitant. The obtained crystals belong to the space group P2(1)2(1)2, with unit cell constants of 84.6 A, 94.1 A, and 117.0 A, consistent with two monomers in the asymmetric unit. They diffract to a resolution of about 2 A and are suitable for X-ray structure determination.
The gram-negative ethanologenic bacterium Zymomonas mobilis is able to grow in media containing high concentrations of glucose or other sugars. A novel compatible solute for bacteria, sorbitol, which enhances growth of Z. mobilis at glucose concentrations exceeding 0.83 M (15%), is described. Added sorbitol was accumulated intracellularly up to 1 M to counteract high external glucose concentrations (up to 1.66 M or 30%). Accumulation of sorbitol was triggered by a glucose upshift (e.g., from 0.33 to 1.27 M or 6 to 23%) and was prevented by the uncoupler CCCP (carbonyl cyanide m-chlorophenylhydrazone; 100 microM). The sorbitol transport system followed Michaelis-Menten kinetics, with an apparent Km of 34 mM and a Vmax of 11.2 nmol.min-1.mg-1 (dry mass). Sorbitol was produced by the cells themselves and was accumulated when growing on sucrose (1 M or 36%) by the action of the periplasmic enzyme glucose-fructose oxidoreductase, which converts glucose and fructose to gluconolactone and sorbitol. Thus, Z. mobilis can form and accumulate the compatible solute sorbitol from a natural carbon source, sucrose, in order to overcome osmotic stress in high-sugar media. No other major compatible solute (betaine, proline, glutamate, or trehalose) was detected.
Glucose-fructose oxidoreductase (GFOR) is a periplasmic enzyme of the ethanologenic, Gram-negative bacterium Zymomonas mobilis. It contains tightly bound NADP+ as cofactor. In Z. mobilis GFOR-recombinant strains, a precursor form of GFOR was accumulated. To assay the preGFOR for its NADP(H) content and enzymatic activity, it was purified from an overproducing strain. Using SDS-PAGE, the precursor subunit size was determined to approximately 45 kDa (compared with a 40 kDa subunit size for the mature GFOR subunit). The N-terminal amino acid sequence of the precursor was determined. The N-terminal residues of the GFOR matched with the signal sequence from the DNA sequence of the gene gfo. The precursor form of GFOR was enzymatically active and contained the cofactor NADP(H).
The informatics team of the Stomatological Society of the GDR provides a complete list of presently available program packages for home, 8 and 16-bit computers and a list of the programming teams. Main developments for the use of PC's in stomatology are described as well. By establishing clear lines for the development of software, standardized user software can be guaranteed.
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The density distribution of human mononuclear blood leukocytes was studied in order to define the optimal conditions for the separation of monocytes and lymphocytes by isopycnic centrifugation. Under standardized conditions, two populations of cells with partially overlapping, normally distributed densities were consistently found. The cells with the lowest density were recognized as monocytes, using phagocytosis and size distribution analysis as criteria. Since the density of monocytes continuously increased during the centrifugation, optimal separation of monocytes and lymphocytes could only be achieved by limiting the time of centrifugation to 10 min at 2200 g and 4 degrees C. The separation on discontinuous density gradients decreased when the load exceeded 8 X 10(6) mononuclear cells per sq cm. Analysis of the composition of the two cell populations obtained after separation on a three-layer discontinuous gradient revealed that the contamination of the monocytes with lymphocytes was due to the partial overlapping density distributions of both cell types. A small and a large scale method for isolation of monocytes from blood on discontinuous density gradients are presented. Under the described conditions, a preparation of functionally intact monocytes can be obtained which is comparable, both in yield and purity, to those obtained by methods based on surface adherence without the drawbacks of the latter methods.
A virtually complete absence of glutathione reductase activity was found in the erythrocytes of all three children (one male, two females) from a consanguineous marriage. Intermediate values were found in the erythrocytes of both parents. The enzyme activity could not be restored either by addition of FAD in vitro or by administration of riboflavin in vivo. The amount of reduced glutathione in the erythrocytes was normal in each case. Severely diminished glutathione stability during incubation with acetylphenylhydrazine was observed in the erythrocytes of the siblings, as well as intermediate stability in the parents' red cells. Clinically, this deficiency was manifested by hemolytic crises after eating fava beans in the eldest daughter (patient), and possibly by cataracts in her own and in her brother's eyes. Very low activities of glutathione reductase were also found in the leukocytes of this family: 13%-15% of normal values for the children and 64%-66% for the parents. Moreover, the same deficiency was found in the purified white blood cells of the propositus: 8% of normal values in the polymorphonuclear (PMN) cells, 4% in the lymphocytes, and 15% in the monocytes, together with 11% in the platelets. Finally, we found an abnormal oxygen consumption of the propositus' PMNs after phagocytosis of zymosan particles, suggesting that the glutathione reductase reaction was involved in the bactericidal capacity of these cells.
During a study on the separation of human blood monocytes from lymphocytes, a method was developed to recognize and count monocytes by electronic means. Lightscattering (Cytograf, Bio/Physics), and changes in electrical resistance (Channelyzer, Coulter) were used to size mononuclear leukocytes directly in cell suspensions. Both methods revealed a size distribution profile in which two populations of mononuclear leukocytes could be distinguished. The largest cells were virtually eliminated after phagocytosis of iron particles. We confirmed that these cells were monocytes by three different criteria: the intracellular lysozyme activity, the number of phagocytes, and the percentage of cells with kidney-shaped nuclei. The highly significant correlations we found showed that monocytes could be recognized and counted by electronic sizing. For this method, purified mononuclear leukocyte preparations had to be used, since the presence of erythrocytes, platelets, and polymorphonuclear cells interfered. Statistical analysis revealed that electronic sizing permitted discrimination of differences in monocyte content of 4.5%, with a probability of 95%. It was calculated that this sensitivity of electronic monocyte counting was about three times higher than the sensitivity of microscopic methods. Since 100,000 cells can be sized within a few seconds, not only the efficiency of the preparation but also minor changes in the size of monocytes and lymphocytes introduced during the isolation can be followed.
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