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Biomedical subjects

M Zulauf

Publications and source records attributed to M Zulauf.

At least 19 recordsLinked to original sources
PubMed1992

Stoichiometry of interaction between interferon gamma and its receptor.

The biological response of interferon gamma is mediated by binding to a specific cell-surface receptor. We investigated the stoichiometry of this binding using soluble receptors produced in prokaryotic and eukaryotic expression systems comprising the extracellular ligand-binding domain of the native protein. The ligand-receptor complexes were analyzed by cross-linking, chromatography, analytical ultracentrifugation and laser-light scattering. Cross-linking and chromatography showed that the stoichiometry of the interaction between ligand and receptor depends on the molar ratios of the two components mixed. All approaches confirmed that mixtures of ligand-receptor complexes are formed with one interferon-gamma dimer bound by one or two receptors. The soluble receptor produced in Escherichia coli mainly showed a ligand/receptor stoichiometry of 1:1, while the receptors produced in eukaryotic cells showed a stoichiometry of binding of 1:2. This apparent discrepancy is most likely due to the conformational heterogeneity of the Escherichia-coli-derived protein.

Amino Acid Sequence↗
PubMed1992

Long-term fluctuation of the visual field in glaucoma.

We examined 756 automated threshold visual fields of 167 eyes of patients with glaucoma to determine the magnitude of the long-term fluctuation at individual test locations. Eyes were grouped into clinically stable or nonstable groups according to predefined clinical criteria. At individual test locations with initial sensitivities of 25 to 30 dB in clinically stable eyes, the 5th to 95th percentile value for subsequent measurements was +/- 4 dB. For initial sensitivities of 20 dB, this 90% range was +/- 6 dB, and for sensitivities 15 dB or less, the 90% range of subsequent values spanned sensitivities from almost zero to normal values. Long-term fluctuation correlated with short-term fluctuation (r = .363, P less than .0005), but not with age or intraocular pressure. There was no correlation of long-term fluctuation with eccentricity after correcting for the decreased sensitivity associated with greater eccentricity. Long-term fluctuation was greater in the nonstable group than in the stable group (P less than .0005). These data provide limits for fluctuation in stable patients with glaucoma, which will help guide clinical decisions about visual field progression.

Adult↗
PubMed1992

2D crystallization: from art to science.

The techniques as well as the principles of the 2D crystallization of membrane and water-soluble proteins for electron crystallography are reviewed. First, the biophysics of the interactions between proteins, lipids and detergents is surveyed. Second, crystallization of membrane proteins in situ and by reconstitution methods is discussed, and the various factors involved are addressed. Third, we elaborate on the 2D crystallization of water-soluble proteins, both in solution and at interfaces, such as lipid monolayers, mica, carbon film or mercury surfaces. Finally, techniques and instrumentations that are required for 2D crystallization are described.

Aluminum Silicates↗
PubMed1992

Number of stimuli as a reliability parameter in perimetry.

Catch trials test patient performance during automated, static perimetry, but their adequacy to estimate reliability is uncertain even though up to 10% of the test time is reserved for catch trials. The 308 visual fields (program G1, all 3 phases, Octopus 201) of 308 eyes of 308 glaucoma, suspected glaucoma, and normal subjects were studied. The 108 visual fields (mean sensitivity > 10 dB; corrected loss variance < 50 dB2) without false responses to catch trials were considered reliable. A multiple linear regression analysis of these 108 fields was performed and revealed the following result (r2 = 0.751): Number of stimuli = 480 + (40.short-term fluctuation) + (8.8.the square root of the index corrected loss variance) - (2.2.mean sensitivity). This equation was used to estimate the number of stimuli required of a reliable subject to complete an examination. Excess stimuli would thus be a sign of reduced reliability. The difference between the estimated and the actual number of stimuli was called the 'stimulus discrepancy'. In 169 fields with false-positive and 58 fields with false-negative responses, the false-positive and false-negative responses correlated with the 'stimulus discrepancy' (r = 0.19, P = 0.014; r = 0.29, P < 0.026, respectively). The number of stimuli depends not only on reliability but also on the software and hardware of the perimeter. 'Stimulus discrepancy' may be an additional useful perimetric reliability parameter which does not require extra testing time.

Adult↗
PubMed1991

Density determination by analytical ultracentrifugation in a rapid dynamical gradient: application to lipid and detergent aggregates containing proteins.

A rapidly developing dynamical gradient can be formed in the analytical centrifuge when a buffer solution prepared in D2O is underlayered under the same buffer solution prepared in H2O in a specially designed double sector cell. In a short time the boundary layer spreads to form the gradient. Heavy particles (S greater than or equal to 10S) will band in the gradient corresponding to their density, which can be determined accurately. To this end, the buffer may contain density adjusting additives such as sucrose. We present results with this technique for lipid vesicles, for a Ca-antagonist bound to vesicles, as well as for a lipoprotein and reconstituted regular membrane protein-lipid arrays.

Animals↗
PubMed1991

Recombinant 55-kDa tumor necrosis factor (TNF) receptor. Stoichiometry of binding to TNF alpha and TNF beta and inhibition of TNF activity.

The extracellular domain of the 55-kDa TNF receptor (rsTNFR beta) has been expressed as a secreted protein in baculovirus-infected insect cells and Chinese hamster ovary (CHO)/dhfr- cells. A chimeric fusion protein (rsTNFR beta-h gamma 3) constructed by inserting the extracellular part of the receptor in front of the hinge region of the human IgG C gamma 3 chain has been expressed in mouse myeloma cells. The recombinant receptor proteins were purified from transfected cell culture supernatants by TNF alpha- or protein G affinity chromatography and gel filtration. In a solid phase binding assay rsTNFR beta was found to bind TNF alpha with high affinity comparable with the membrane-bound full-length receptor. The affinity for TNF beta was slightly impaired. However, the bivalent rsTNFR beta-h gamma 3 fusion protein bound both ligands with a significantly higher affinity than monovalent rsTNFR beta reflecting most likely an increased avidity of the bivalent construct. A molecular mass of about 140 kDa for both rsTNFR beta.TNF alpha and rsTNFR beta.TNF beta complexes was determined in analytical ultracentrifugation studies strongly suggesting a stoichiometry of three rsTNFR beta molecules bound to one TNF alpha or TNF beta trimer. Sedimentation velocity and quasielastic light scattering measurements indicated an extended structure for rsTNFR beta and its TNF alpha and TNF beta complexes. Multiple receptor binding sites on TNF alpha trimers could also be demonstrated by a TNF alpha-induced agglutination of Latex beads coated with the rsTNFR beta-h gamma 3 fusion protein. Both rsTNFR beta and rsTNFR beta-h gamma 3 were found to inhibit binding of TNF alpha and TNF beta to native 55- and 75-kDa TNF receptors and to prevent TNF alpha and TNF beta bioactivity in a cellular cytotoxicity assay. Concentrations of rsTNFR beta-h gamma 3 equimolar to TNF alpha were sufficient to neutralize TNF activity almost completely, whereas a 10-100-fold excess of rsTNFR beta was needed for similar inhibitory effects. In view of their potent TNF antagonizing activity, recombinant soluble TNF receptor fragments might be useful as therapeutic agents in TNF-mediated disorders.

Animals↗
PubMed1991

Efficient purification of recombinant human tumor necrosis factor beta from Escherichia coli yields biologically active protein with a trimeric structure that binds to both tumor necrosis factor receptors.

A fast and efficient method for medium scale purification of recombinant human tumor necrosis factor beta (rTNF-beta) from Escherichia coli cells is described. The purified rTNF-beta displayed biological activity similar to rTNF-alpha in a WEHI 164 cell cytotoxicity assay. The titration curve of rTNF-beta and elution profiles of rTNF-beta in gel filtration experiments were different from those of rTNF-alpha. However, light scattering and ultra-centrifugation studies showed that both cytokines have trimeric structures in solution at 0.5 mg/ml, with minor differences in the distribution of nontrimeric species. rTNF-beta bound to purified 55- and 75-kDa TNF receptors with high affinity. The binding of rTNF-beta to either receptor was analyzed on Scatchard plots and compared with that of rTNF-alpha.

Binding, Competitive↗
PubMed1991

Mass analysis of bacteriophage T4 proheads and mature heads by scanning transmission electron microscopy and hydrodynamic measurements.

Quantitative mass analysis of bacteriophage T4 proheads by scanning transmission electron microscopy (STEM) revealed a mass of 79.5 +/- 0.6 MDa, while hydrodynamic measurements yielded a prohead mass of about 80 MDa. This is 25% less than the prohead mass deduced from its polypeptide composition, and this finding implies that the bacteriophage T4 prohead is built of fewer polypeptide copies than previously reported. In contrast, the mass of mature heads measured by STEM, 194 +/- 2 MDa, is in agreement with previous mass measurements of DNA and protein content, and it is consistent with the previously determined stoichiometry. This good agreement of average STEM values for proheads and mature heads with corresponding hydrodynamic measurements suggests that STEM allows faithful evaluation of the masses of large supramolecular assemblies (i.e., greater than or equal to 200 MDa) such as whole viruses or cellular organelles.

Formaldehyde↗
PubMed1990

Threshold perimetry in tilted disc syndrome.

Twelve consecutive patients (17 eyes) with tilted disc syndrome underwent quantified visual field examination with the G1 Octopus program (Interzeag AG, Schlieren, Switzerland). Visual fields were abnormal in all cases. Although field loss was more pronounced in the superotemporal quadrant (P less than .001), it also involved the other three quadrants, thus demonstrating that optic nerve hypoplasia in tilted disc syndrome is apparently not entirely sectorial. Linear regression analysis showed that an increase in mean defect correlated with increase in myopic refractive error (P less than .05). However, the increase in myopic refractive error was found to be related to a decrease in corrected loss variance (P less than .05), indicating that in tilted discs with higher myopia, field loss is more homogeneous. With this series of patients, short-term fluctuation was within normal ranges in all visual fields, showing that this may be an additional clue for differential diagnosis from acquired disorders.

Adult↗
PubMed1990

Quantification of angioscotomas.

The current normal visual-field indices to quantify scotomas are not applicable to the stimuli in angioscotometry. Therefore, different alternative methods for the quantification of angioscotomas are presented and discussed. The proposed method for quantification of angioscotomas can easily be calculated with commercially available statistical programs by every physician interested in statistics. A program for angioscotometry including an index calculation is proposed. Three examples illustrate the possible alternative calculations.

Adult↗
PubMed1990

Pindolol and timolol: short-term influence on angioscotomas and static brightness contrast sensitivity.

In a double-masked, short-term study on 12 healthy elderly volunteers, angioscotomas and contrast sensitivities were measured 2 h after treatment with placebo, pindolol 1% and timolol 0.5%. In perimetry, angioscotomas did neither change in deepness nor in diameter significantly. However, the mean differential light sensitivity was highest with timolol (15.5 dB) and lower with pindolol (15.2 dB p less than 0.018) and placebo (15.0 dB; p less than 0.004). In contrast sensitivity testings, the mean contrast sensitivity was lowest with timolol (15.0 dB) and higher with pindolol (15.3 dB p less than 0.001) and placebo (15.7 dB; p less than 0.001). The differences between pindolol and placebo were not significant in both tests. The contrasting results may be explained by the locations where retinal sensitivity was tested, near or far from retinal vessels i.e. foveally or near the blind spot. Pharmacologically, the main difference between the two medications is the intrinsic sympathomimetic activity of pindolol.

Aged↗
PubMed1988

Spatial brightness contrast sensitivity measured with white, green, red and blue light.

Grating contrast sensitivity was measured using different colors and different grating orientations. The contrast sensitivity was highest when measured with green light, a little less when measured with red light, and lowest with blue light. The contrast sensitivity with blue light was relatively low compared with green and red light for high spatial frequencies, and relatively high for low spatial sensitivities. The so-called 'oblique effect' was confirmed in this study, but a difference between horizontal and oblique gratings was only found in spatial frequencies higher than 18 cycles/degree. The present study, carried out on 20 persons, suggests that the inter- and intraindividual components of variance are smallest when measured with green light and vertically oriented gratings.

Adolescent↗
PubMed1988

Influence of age on the transparency of the lens in normals: a population study with help of the Lens Opacity Meter 701.

The Lens Opacity Meter 701 measures the lens density quantifying the back light scatter of the lens. The instrument emits a modulated dark-red beam which runs along the optic axis of the lens. The stray light is converted into an electrical impulse which is displayed and printed using a numerical scale. The lens density in a normal population was investigated with this instrument in order to study the influence of age on the opacification process.

Adolescent↗
PubMed1988

Short-term influence of alcohol on spatial brightness contrast sensitivity.

The present crossover, controlled study demonstrates that alcohol at a blood concentration of approximately 0.08% reduces the contrast sensitivity (p less than 0.001). The mean contrast sensitivity was 15.03 dB in the control measurements and 14.39 dB in the measurements with alcohol. Brightness contrast sensitivity was measured with white, green, red and blue light, in this sequence. Therefore, the test design may present time effects as well as 'color effects'. The mean decrease in contrast sensitivity was with white light -1.26 dB, with green light -0.88 dB and with red light -0.57 dB. Contrast sensitivity tested with blue light showed even a slight increase with alcohol (+0.12 dB). The time interval between alcohol consumption and the test was important (p less than 0.001). The mean decrease in contrast sensitivity with alcohol in subjects with a short interval of 40 min was less reduced (-0.3 dB) than in subjects with a long interval of 60 min (-0.98 dB). In summary, at moderate doses of alcohol, contrast sensitivity is only moderately decreased and this decrease depends on the time between alcohol consumption and the test.

Adolescent↗
PubMed1986

The influence of alcohol on the outcome of automated static perimetry.

It is well known that perimetric findings fluctuate within a single examination. There is additional fluctuation between perimetric examinations. The cause of this fluctuation is not yet fully understood, but such things as changes in attention, patient cooperation, or drugs have been discussed. To study such possible factors, we carried out perimetry on subjects who had consumed alcohol and who had not. The results indicate that alcohol, at a blood concentration of approximately 0.08%, barely influences the results of static automated perimetry. Differential light sensitivity remained unchanged by alcohol at all eccentricities tested. A decrease in the ability to cooperate was manifested by a significant higher score of false-positives in catch trials. There was also a tendency toward an increase in false-negative responses in catch trials, an increase in the number of stimuli presentations required, and higher short-term fluctuation. Lack of the influence of alcohol on the differential light threshold does not necessarily mean that alcohol has no influence on visual function. It indicates, however, that differential light sensitivity, as measured with the automated perimeter Octopus, is not influenced by moderate alcohol ingestion.

Adolescent↗