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Biomedical subjects

K O Greulich

Publications and source records attributed to K O Greulich.

49 records · Page 3Linked to original sources
PubMed1985

Nucleosome core particle structure and structural changes in solution.

The radius of gyration, Rg, of chicken erythrocyte nucleosome core particles, was found to be 4.56 (+/- 0.07) nm by small-angle X-ray scattering, independent of particle concentration and of NaCl concentration between 0.1 M and 0.6 M-NaCl. The large, positive, second virial coefficient, A2, from particle concentration dependence (but independent of NaCl concentration) in small-angle X-ray scattering may indicate non-electrostatic repulsive ordering over large distances. Density contrast variation in equilibrium sedimentation with a small probe (sucrose) and a larger probe (gamma-cyclodextrin) yields good results for core particle hydration in the first instance, and for an estimate of the total particle volume in the second instance.

Animals↗
PubMed1985

Time resolved fluorescence of bacteriophage Pfl DNA binding protein and its complex with DNA.

The DNA binding protein of the filamentous bacteriophage Pfl exhibits fluorescence from a single tryptophan residue. The location of the emission maximum at 340 nm ist quite common for proteins, but the single lifetime of 7.8 ns is one of the longest yet reported. Protein fluorescence is quenched more efficiently by Cs+ than by I-; the Trp is located in a partially exposed pocket, in the vicinity of a negative charge. In the native complex of the binding protein with Pfl DNA the fluorescence emission maximum is at 330 nm, indicating a more apolar environment for Trp 14. The native nucleoprotein complex exhibits a similar fluorescence lifetime (6.5 ns) and an approximately equal fluorescence yield, indicating the absence of Trp-DNA stacking. The tryptophan in the complex is virtually inaccessible to ionic quenchers, and thus appears to be buried. Fluorescence depolarisation measurements have been used to examine the rotational mobility of the tryptophan in the protein and in the nucleoprotein complex. In the protein alone a single rotational correlation time (phi) of approximately 19 ns is observed, corresponding to rotation of the entire dimeric molecule; in the native nucleoprotein complex with Pfl DNA, a phi of approximately 500 ns is observed, corresponding to a rigid unit of at least 50 subunits. In neither case does the tryptophan exhibit any detectable flexibility on the subnanosecond time scale.

Bacteriophages↗
PubMed1984

Estimation of tyrosine-40-DNA distance in the filamentous phage Pf1 by analysis of its intrinsic fluorescence properties.

Iodination of the exposed Tyr-25 in the coat protein decreases the fluorescence intensity of the filamentous phage Pf1 to less than 3% of its original fluorescence. If one assumes that the total residual fluorescence originates from the non-iodinated, buried Tyr-40, one can estimate the distance between Tyr-40 and the DNA bases in Pf1 to be less than 7 A, making use of the Foerster law for fluorescence energy transfer. The result is consistent with the idea that Tyr-40-DNA interaction is responsible for the unusually large axial base separation in Pf1-DNA.

Bacteriophages↗
PubMed1979

The use of an oscillating-tube densitometer as a tool in enzyme kinetics. Determination of the influence of sodium ascorbate on invertase, dextransucrase and dextranase.

The use of a commercial oscillating-tube densitometer with an accuracy of 4 . 10(-7) g/cm3 for the determination of enzyme-kinetics constants is tested. This method is applied to the investigation of the influence of vitamin C (sodium ascorbate) on the glycolytic enzymes invertase, dextransucrase and dextranase. Invertase is inhibited uncompetitively, dextransucrase non-competitively. There is no significant effect of the vitamin on dextranase. The comparison of the mechanisms of the three enzymes suggests that only those reaction steps are inhibited by vitamin C in which fructose is released from the enzyme.

Ascorbic Acid↗
PubMed1978

Volume changes during enzyme reactions. The influence of pressure on the action of invertase, dextranase and dextransucrase.

The pressure dependence of the maximum velocities and the Michaelis constants for the enzymes invertase and dextranase was measured up to 1400 bar. The corresponding activation volumes deltaV not equal to c and deltaV not equal to Km proved to be independent of pressure. Together with data from other sources the meaning of deltaV not equal to c and deltaV not equal to Km is established and the volume profiles of the reactions are constructed. These profiles are similar in contour to the volume profile of the dextran formation catalyzed by the enzyme dextransucrase, but the amount of the volume changes is very much larger for dextransucrase. The evaluation of salt effects shows, that for all three enzymes solvent interactions are not important in explaining the results. The reaction mechanisms seem to be governed by conformation changes of the enzymes. The larger effects in dextransucrase are explained by the produced dextran chain remaining tightly bound to the enzyme and being transported relative to the enzymes position in each reaction cycle.

Dextranase↗
PubMed1976

High pressure enzyme kinetics of dextransucrase.

The pressure dependence of enzymatic dextran formation has been observed up to 1000 at for several substrate concentrations. First order denaturation effects could be separated from the thermodynamic effects, which lead to a volume of 30.4 to 44.0 ccm per mole for the formation and -13.6ccm per mole for the activation of the enzyme-substrate complex. Denaturation depends on the substrate concentration. This leads to the conslusion that only the free enzyme is denatured, wheras the ES complex is stable.

Dextrans↗
PubMedDate not supplied

Chromosome microtechnology: microdissection and microcloning.

The physical microdissection of chromosomes and subsequent microcloning of dissected fragments is enabling the generation of very large numbers of cloned unique sequences from defined chromosomal regions. In addition to use in constructing region-specific libraries of the entire human genome and providing probes for mapping and sequencing purposes, such chromosome microtechnology should facilitate the search for disease-associated genes in defined chromosome regions.

Chromosomes↗
PubMedDate not supplied

Cell viability of retinal photoreceptor evaluated by polar distribution of Ca(2+) and electrical charge.

The polar organisation is characteristic to the living cell and disappears with the cell functional decay. Here we report experimental evidence that frog retinal photoreceptor rod cell shows a polar distribution of the electrical charge and of free cytosolic Ca(2+) along its length. Retinal rod cells were loaded with Calcium sensitive dye (Green1) and examined under fluorescence microscopy coupled with an image analysis system. In addition, suspension of rod cells was placed in direct current electric field for electrical polarity assessment. Both polar Ca(2+) and electrical charge distribution can be objectively measured and quantified providing thus a fine test for cell viability. Such a test is required in checking the functional integrity of photoreceptors used in retinal transplant.

Animals↗
PubMedDate not supplied

Fluorescence microscopic observation of catalysis by single or few LDH-1 enzyme molecules.

Lactate dehydrogenase (LDH-1) catalyzes the reaction of lactate and nonfluorescent NAD+ to pyruvate, NADH (fluorescence at lambda em = 455 nm, lambda em = 365 nm) and H+. The injection of highly diluted LDH-1 solution into a drop of substrate solution results in the formation of a bubble of enzyme inside the drop of substrate. At the contact surface between the enzyme solution and the substrate, discrete and statistically distributed zones of increasing fluorescence intensity and different size can be observed after enzyme injection. These zones can be interpreted as clouds of NADH around a single or a few enzyme molecules. The kinetics of the NADH formation in every fluorescent zone, and the size of the zone, can be described by a zero order production combined with a diffusion controlled loss of the reaction's product NADH from the reaction zone. From the dilution of the enzyme solution and from statistical analysis one can conclude that only few enzyme molecules in the center of the fluorescent reaction zones catalyze the NADH formation.

Catalysis↗