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Biomedical subjects

D Zirwer

Publications and source records attributed to D Zirwer.

At least 55 records · Page 3Linked to original sources
PubMed1984

Reconstitution of the liver microsomal monooxygenase system in liposomes from dimyristoylphosphatidylcholine.

Different techniques to incorporate the essential isolated and purified enzymes of the hepatic endoplasmic reticulum into monolamellar dimyristoylphosphatidylcholine vesicles are compared with respect to structural and functional parameters of the reconstituted system. By use of gel penetrating chromatography on Sepharose 4B, dynamic light scattering and electron microscopy the structural properties of the reconstituted system were proved comparing the reduction of P-450 LM2 via the NADPH dependent reductase and by dithionite as well with the microsomal reduction rates and by studying the binding of benzphetamine to P-450 LM2 in soluble and liposomal form.

Animals↗
PubMed1983

How many base-pairs per turn does DNA have in solution and in chromatin? An answer from wide-angle X-ray scattering.

Experimental excess wide-angle X-ray scattering curves from DNA in solution, from Na-DNA crystallites in mother-liquor, from mononucleosomes in solution and from nucleosome core histone complexes are compared with each other and with calculated excess scattering curves of DNA with variable number of base-pairs per turn. The DNA in the Na-DNA crystallites and in the mononucleosomes has on average the canonical B-conformation which is well-known from fibre-diagrams with 10 base-pairs per turn and a rise of 0.34 nm per base-pair. The averaged structure of DNA in solution differs from this conformation. The model which fits best this structure has 10.8 base-pairs per turn and a rise of 0.34 nm per base-pair.

Animals↗
PubMed1982

Auto-oxidation-induced fusion of lipid vesicles.

Spontaneous size changes of small unilamellar vesicles with initial mean diameters of 25 nm measured by quasi-elastic light scattering (QELS) and electron microscopy are reported. After the size conversion the vesicles have mean diameters of about 70 nm and are of the unilamellar and multilamellar type. The fact that auto-oxidation initiates this process is established by the comparison of the results for vesicles which differ only in the degree of auto-oxidation. The role of phosphatidylcholine hydroperoxides as fusogens is discussed.

Light↗
PubMed1980

Hydrodynamic and quasi-elastic light scattering studies on the 12S globulin from rapeseed.

The 12S globulin, one of the major storage proteins of rapeseeds, has the following physico-chemical constants, as determined by ultracentrifugation, quasi-elastic light scattering measurements and gel chromatography: sedimentation coefficient S20(0), w = 12.7 x 10(-13) s; diffusion coefficient (quasi-elastic light scattering) D20(0), w = 3.8 x 10(-7) cm2 S-1; Stokes radius (by quasi-elastic light scattering) Rs = 5.7 nm and (by gel chromatography) Rs = 5.5 nm; partial specific volume (calculated from the amino acid composition) v(-) = 0.729 ml g-1; molecular weight Ms, D = 300,000 daltons, Ms, Rs = 294,000 daltons (Rs from the gel chromatography); frictional ratio f/fo = 1.28.

Brassica↗
PubMed1979

Spermine-DNA complexes build up metastable structures. Small-angle X-ray scattering and circular dichroism studies.

Spermine-DNA complexes have been examined by small-angle and wide-angle X-ray scattering as well as by circular dichroism studies. Condensed complexes are building up below a critical ionic strength. We have found that at one and the same ionic strength condensed complexes having two different supramolecular structures (Type I and Type II) can coexist. The structure of the condensates depends on the method of condensate formation. Phase transitions between these structures can be induced by thermal treatment. We conclude from these facts that with polyamine-DNA condensates metastable structures are of importance.

Animals↗
PubMed1978

Study of DNA-spermine interactions by use of small-angle and wide-angle X-ray scattering and circular dichroism.

Circular dichroism measurements with DNA-spermine complexes at 0.075 M NaCl and at 0.15 M NaCl reveal +psi (type I) and -psi (type II) CD spectra respectively. From small-angle X-ray scattering studies it could be shown that type I has a long-range order, short-range order supramolecular structure, while type II is of long-range disorder, short-range disorder structure. The secondary structure of the DNA in both types of condensates is B-like as concluded from wide-angle X-ray scattering diagrams of the condensates and from a comparison with the wide-angle X-ray curves of DNA and RNA in solution.

Animals↗
PubMed1978

[Secondary structure of condensed DNA. wide-angle, small-angle x-ray scattering and circular dichroism].

Ethanol precipitated DNA shows a CD spectrum of the +psi-type which is similar to that of DNA in the A-form. DNA condensed with cetyl-trimethylammonium-bromide shows, depending on the condensation velocity, a CD spectrum of the -psi-type, or a CD spectrum only slightly modified from that of DNA in solution. The first spectrum is similar to that of DNA in the C-form, and the second one, to that of DNA in the B-form. Using large-angle X-ray scattering of the three DNA condensates and comparing them with the scattering curves calculated from the atom coordinates for the A-, B-, and C-form of DNA it is shown that the secondary structure of the DNA belongs in all three cases to the B-family. It follows from this result that the secondary structure of DNA alone does not determine the type of CD spectrum. The CD spectrum of condensed DNA is essentially determined by the supramolecular structures of the partially crystalline DNA condensates. These supramolecular structures can be demonstrated by the small-angle X-ray diagrams. The condensation of DNA by ethanol and cetyl-trimethylammonium-bromide proceeds in the form of a partial crystallization of the DNA.

Animals↗
PubMed1977

[Diffuse x-ray wide-angle scattering of polyglutamic acid in solution].

The diffuse wide angle x-ray scattering (WAXS) of polyglutamic acid (PGA) in solution was studied using an x-ray diffractometer with small aperture of the primary beam. The scattering curve was recorded at an angular interval from (article: see text). The experimental scattering intensity of PGA with alpha-helical CD spectrum showed a maximum at 14.4 nm-1. Unordered PGA in solution yielded no maximum at this scattering angle. The studies have proved that the scattering theory can be applied to globular proteins in solution as well as to chain molecules in solution in this angular interval. The differences between the calculated scattering curves and the experimental curves indicate minor movements of the side chains of PGA in solutions and slight structuring of the solvent at the surface of the polypeptide chain.

Glutamates↗
PubMed1977

Substrate binding to solubilized cytochrome P-450 from rabbits at different temperatures.

The binding affinities of selected type I- and type II-substrates to partially purified cytochrome p-450 from rabbit liver microsomes were studied and found to differ from those of rats. The temperature dependence of the apparent binding constants qualitatively exhibited the same characteristics compared with that of rats. For type I-substrates endothermic and for type II-substrates exothermic reaction characteristics were observed. Taking into account the partition coefficients of the substrates so far investigated it is obvious that type I substrates with increasing hydrophobicity are bound more strongly while type II-substrates show a more complicated behvaiour. This may due to the fact that other types of binding are included besides the hydrophobic interactions.

Animals↗
PubMed1976

Circular dichroism studies on DNA condensed in NaCl cetyltrimethyl ammonium bromide solutions.

It is shown by means of circular dichroism studies of variously condensed forms of DNA that the specific supramolecular structure of DNA determines the type of CD spectra. DNA, condensed (crystallized) slowly in the presence of cetyltrimethyl ammonium bromide yields a spectrum very similar to that of DNA in solution in the B-form. The condensates appear in the phase-contrast microscope as spherulitic crystallites. Rapidly condensed DNA in the presence of cetyltrimethyl ammonium bromide shows a spectrum of the psi-type with large negative ellipticites. The influence of condensation velocity upon the supramolecular structure of DNA gives evidence that the various condensation forms of DNA are not thermodynamical equilibrium conformations.

Bromides↗
PubMed1976

Folding crystallization of DNA. Circular dichroism studies.

CD spectra of DNA monocrystals are extremely different from spectra of psi-DNA or DNA-histone H1 or DNA-polylysine complexes. They are discussed to be dependent on the supramolecular organization of DNA in the condensed form, and they are not in contradiction to the previously proposed seven folding model of DNA in chromatin. Conclusions are drawn with regard to the interpretation of chromatin CD spectra.

Chromatin↗
PubMed1976

Differentiation between type I and type II substrate binding to cytochrome P-450 by variation of temperature.

The binding affinities of type I- and type II-substrates to cytochrome P-450 solubilized from phenobarbital induced rat liver microsomes in dependence on the temperature have been determined. Both classes of substrates have been found to exhibit different temperature behaviour. The tendency of type I-substrates (benzphetamine and hexobarbital) to form complexes increases with increasing temperature; type II-substrates show the inverse tendency. From the van't Hoff plot the binding enthalpy was calculated and discussed in connection with the entropy and free enthalpy values. These data ascertain the suggestion of different binding sites for both classes of substrates.

Aniline Compounds↗
PubMed1975

[Interaction of substrate with cytochrome P-450 in microsomal and solubilized form].

In order to characterize the substrate binding sites, difference spectroscopic titrations in microsomal and solubilized cytochrome P-450 from induced and non-induced rat liver microsomes were performed. The binding constants determined show differences depending on the physicochemical nature of the substrate and the degree of integration of the enzyme system. In hydrophilic substrates the differences of the binding to the microsomal or solubilized form are less pronounced than in lipophilic ones. From the comparison of the parameters obtained at various levels of integration it is concluded that the micromilieu of the binding site is of great importance for the binding of the substrate of cytochrome P-450.

Animals↗