Effect of solvent phase transitions on enzymatic activity and structure of laccase from Coriolus hirsutus.

The effect of solvent phase transitions on catalytic activity and structure of the active site of laccase produced by the Basidiomycetes Coriolus hirsutus 072 was studied. As shown by small-angle X-ray scattering, laccase exists in solution as a mixture of monomeric and aggregated particles in the percent ratio 85:15. This ratio did not change on phase transitions. A complex nature of laccase activity dynamics during thawing and further heating to 20 degrees C was shown. Spontaneous oxidation of T1 copper center in the temperature range 12-20 degrees C was not observed. According to spectral data, the structure of laccase active sites including all copper centers of types T1, T2, and T3 changes during the phase transition.

[Some X-ray diffraction parameters of liquid-crystalline dispersions of nucleic acid-chitosan complexes ]. / Nekotorye rentgenograficheskie parametry zhidkokristallicheskikh dispersii kompleksov NK-khitosan.

Liquid-crystalline dispersions of nucleic acid-chitosan complexes (NA-chitosan) possess optical and X-ray diffraction properties different from those of "classical" cholesterics. It is possible that positive charge distribution (distance between charges, chitosan conformation, etc.) in the polymeric chain of chitosan molecule combining with NA molecule is the factor that affects the spatial structure of resulting dispersions.

Liquid-crystalline structure of nucleic acids: effect of antracycline drugs and copper ions.

The formation of liquid-crystalline dispersions (L.C.D.) from double-stranded DNA and polynucleotide (NA) molecules complexed with a number of anthracycline derivatives was investigated. These drugs form two types of complexes (complex I and complex II) with NA, which differ in the mode of drug orientation in respect to the NA helical axis. When complex II forms, addition of copper ions causes bridging of neighboring NA molecules through polymeric copper-anthracycline links (Figure 1). This results in an extra-increase in the amplitude of the intense CD band, characteristic for complex II, in the drug absorption region. Comparison of data obtained for different analogs and derivatives of daunomycin, has shown that the presence of 4 coordinating oxygen atoms at positions 5,6 and 11,12 (or 1,12) of the anthracycline ring system represents the basic prerequisite for the formation of a long polymeric chelate bridge after addition of copper ions. A second requirement relates to the chemical and stereochemical properties of sugar residues at position 7. These are important for proper positioning of the neighboring anthracycline aglycones in the polymeric chelate bridges and for spatial fixation of Cu2+ ions. Base sequence of double-stranded polynucleotides plays, if any, a minor role in polymeric chelate bridge formation. The question concerning the sterical orientation of two neighbouring antracyclines in the linking bridges, formed between NA molecules fixed in the liquid-crystalline structure, remains open.

Loosening of the phage structure in a low ionic strength environment.

Structural parameters of phage T7 were compared in two frequently used Tris buffers of high and low ionic strength, in order to explain the different biological activity and drug-binding characteristics. Characteristics of the whole phage geometry were obtained by viscosimetry, static and quasi-elastic light-scattering and small-angle X-ray scattering. The latter method revealed dissimilarities in the intraphage DNA compactness, consistent with the findings of the optical absorption melting studies. Alterations in the particle dimensions determined in the same sample by different methods are discussed, and a model is constructed to explain the structural modifications that occur on lowering the ionic strength.

[Formation of the regular, optical isotropic phase of low molecular weight DNA molecules modified by cis-dichlorodiammineplatinum]. / Obrazovanie uporiadochennoi, opticheski izotropnoi fazy molekul DNK nizkoi molekuliarnoi massy, modifitsirovannykh tsis-dikhlorodiamminplatinoi.

It is shown that condensation of DNA molecules of low molecular mass (less than 1 X 10(6) in NaClO4-containing solution of poly(ethylene glycol) brings about formation of cholesteric liquid crystal phase; pattern of this phase is presented. It has been found by means of X-ray analysis and polarization microscopy that at certain level of modification with cis-dichlorodiammineplatinum (II) the DNA molecules instead of cholesteric structure form an ordered optically isotropic phase. The problem about the causes of the formation of such phase and about the pattern of spatial organisation of adjacent DNA molecules in it remains open.

[2 types of temperature transitions in liquid crystals formed from poly(I).poly(C) molecules]. / Dva tipa temperaturnykh perekhodov zhidkikh kristallov, sformirovannykh iz molekul poli(I).poli(C).

The small-angle X-ray scattering curves, CD spectra and textures of the liquid-crystalline phase formed from poly(I).poly(C) molecules in a water-salt solutions containing poly(ethylene glycol) at different temperatures were obtained. It was found that the heating of poly(1).poly(C) liquid-crystalline phase is accompanied by two types of transitions, the first one--a "cholesteric----"compensated" structure----cholesteric", the second--a "cholesteric----isotropic state" transition. The latter transition takes place at a temperature that corresponds to that of the separation of chains of the double-stranded poly(I).poly(C) molecule.

[Mesophase state of double-stranded RNA and polyribonucleotides characterized by high optical activity]. / Mezofaznoe sostoianie dvukhtsepochechnoi RNK i poliribonukleotidov, kharakterizuemykh vysokoi opticheskoi aktivnost'iu.

A small-angle reflexion in X-rayograms and an intense band at A approximately 270 nm in the CD spectrum are assigned to compact particles that arise when mixing water-salt solutions of PEG with water-salt solutions of double-stranded RNA and those of poly(A) poly(U) and poly(I) poly(C). The discrepancy between the 35-40 A small-angle and the approximately 20 A small-angle reflexion typical for double-stranded poly-nucleotide crystals together with the presence of the intense band in the CD spectra point out to the fact that the double-stranded RNA molecules and the molecules of polyribonucleotides exist in a mesophase (liquid crystalline) state. The compact particles of double-stranded RNA and those of polyribonucleotides are shown to be able to have either a positive or a negative band of the CD spectrum depending on PEG concentration, ionic strength or temperature of the solution.

A mesophase (liquid crystal) state of DNA complexes with anthracycline antibiotics.

In the presence of polyethyleneglycol water-salt solutions, DNA is condensed to a kind of mesophase (liquid crystals). The peculiar properties of this phase caused by anisotropic orientations have been analyzed by circular dichroism (CD) of condensed particles of DNA complexed with dyes, i.e. anthracycline antibiotics (daunomycin, aclacinomycin A), actinomycin, and ethidium bromide. The anthracycline complexes show intense CD bands in the visible and the UV region. Daunomycin induces a typical reversal of the sign of these CD bands with increasing occupation of the double helix contrary to the other ligands. This characteristic effect and its partial reversal after removal of daunomycin from the condensed particles can be the result of the change of the direction of the mesophase helical twist owing to an energy change of interaction between DNA molecules, and partially to a modification of base-plane inclination (tilt), too. This new type of DNA complex state is characterized in detail.

[Correlation between conformation distortion of the DNA sugar-phosphate backbone and high optical activity of its compact form]. / O sviazi mezhdu konformatsionnoi neodnorodnost'iu struktury dvukhtsepochechnoi DNK i vysokoi opticheskoi aktivnost'iu ee kompaktnoi formy.

Different physico-chemical methods (CD, ORD, small-angle X-ray diffraction, etc) were used for investigating the properties of the DNA compact particles formed in PEG-containing water-salt solutions. It has been shown that small-angle reflection, characteristic of the DNA compact particles, changes from 36.8 A (CPEG = 140 mg/ml) to 25 A (CPEG = 300 mg/ml). The maximal optical activity (the intense negative CD-band and optical rotation [alpha] = 60 000 degrees) are inherent properties of the DNA compact particles formed at CPEG 120--180 mg/ml. The high optical activity points to the twist of DNA chromophores through the DNA molecule resulting in a long-rang pitch (P approximately 2000A). Such macroscopic superhelical structure (diameter 40--30 A) is due to conformational distortion of the DNA double-helix with alternating "left" and "right" orientation of chromophoes. Disappearance of conformation distortion is accompanied by disappearance of the high optical activity of the DNA compact particles and results in a small-angle reflection of 25 A. Taking into account the reasons of formation of the optically-active DNA compact particles conditions are suggested to conserve high optical activity at CPEG equal to 400 mg/ml.

Preliminary morphological and X-ray diffraction studies of the crystals of the DNA cetyltrimethylammonium salt.

Double-stranded DNA molecules (molecular weight 2.5 X 10(5) - 5 X 10(5) daltons) have been crystallized from water-salt solutions as cetyltrimethylammonium salts (CTA-DNA). Variation of crystallization conditions results in a production of different types of CTA-DNA crystals: spherulits, dendrites, needle-shaped and faceted rhombic crystals, the latter beeing up to 0.3 mm on a side. X-ray diffraction data indicate that DNA molecules in the crystals form a hexagonal lattice which parameters vary slightly with the morphological type of the crystal. Comparison of the melting curves of the DNA preparation before and after crystallization suggests that DNA molecules are partially fractionated in the course of crystallization. Crystals of the CTA-DNA-proflavine complex have also been obtained.

[Study of the structure of bacteriophage DD7 by the small angle of dispersion x-ray method]. / Izuchenie struktury bakteriofaga DD7 metodom rentgenovskogo malouglovogo rasseianiia

The method of roentgen small angle dispersion was used for the study of the structure of bacteriophage DD7. According to the results, phage DD7 is a homogeneous icosahedral particle (with the edge of 410-415 A) with a round cylindrical tail (1700-1750 A in length, 110-120 A in diameter). The lineal sizes of the head exceed those determined by electron microscope approximately by 25%. The thickness of the protein coat of the phage is 25-30 A, that is, 2 times less than that of phages Cd and PB-2. This confirms the assumption that the lipid-containing portion of the phage coat is eliminated by centrifugation in cesium chloride density gradient.