SVIBOR - Papers - project code: 1-03-018

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Published papers on project 1-03-018


Quoted papers: 12
Other papers: 6
Total: 18


  1. Type of paper: Paper in journal

    Title: Non-homogeneous kinetics in the competition of single-stranded calf-thymus DNA and low-molecular weight scavengers. Comparison of experimental data and theoretical models.

    Authors:
    Udovičić, Ljiljana (24971)
    Mark, Franz
    Bothe, Eberhard
    Schulte-Frohlinde, Ditrich
    Journal: Int. J. Radiat. Biol.
    Number: 3
    Volume: 59
    Year: 1991
    Pages: from 677 to 697
    Number of references: 32
    Language: engleski
    Summary: The yield of single-strand breaks induced by Co gama-radiation in single-stranded calf-thymus DNA has been measured in aqueous, N2O/)O2 saturated DNA solutions as a function of the concentration of added OH scavengers. Single-strand break yields have also been determined, relative to the yield of OH radicals, using pulse radiolysis. Essentially the same dependence on scavenging capacity was obtained under both irradiation conditions. At the highest scavenging capacity used (10exp9 s-1), about eight times more strand breaks and formed than would be predicted from homogeneous competition kinetics. The experimental data are compared with values obtained from theoretical models which are based on non-homogeneous kinetics, and includethe effects of spurs and of the direct action of radiation. The comparison shows that the observed dependence of the single-strand break yield on the scavenging capacity can be quantitatively accounted for without the need of empirical adjustment of parameters using a DNA model where the macromolecules are approximated by structureless cylinders of radius RC=080 nm which of their surface react with OH radicals at a diffusion -controlled rate. The factors determining the scavenger dependence of the single-strand break yield are discussed. The increase on going to higher scavenging capacities in the apparent rate constant of the reaction of OH with DNA is rationalized in terms of the mean diffusion length of OH radicals in solution. Estimates are given for the fractions of strand breaks due to randomized OH radicals, OH radicals from spurs, and the direct radiation effect.
    Keywords: Non-homogeneous kinetics, OH radicals, single-strand breaks in DNA

  2. Type of paper: Paper in journal

    Title: Long-range hole migration in irradiated crystals of nucleic acid bases. An EPR study

    Authors:
    Herak, Janko N. (15541)
    Huttermann, Jurgen
    Journal: Int. J. Radiat. Biol.
    Number: 3
    Volume: 60
    Year: 1991
    Pages: from 423 to 432
    Number of references: 28
    Language: engleski
    Summary: Polycrystalline samples of several nucleic acid bases co-crystallized with small amounts of thioanallogues as impurites were X-irradiated at 77 K and investigated by electron paramagnetic resonance (EPR) spectroscopy for sulphur (S)-centred radicals. Anhydrous cytosine, cytosine monohydrate and cytosine hydrochloride with 0,01-1% incorporated thiocytosine gave strong EPR signals charasterisric of S-centred radicals, with spectroscopic parameters different from those for irradiated thiocytosine alone. Likewise, in guanine hydrochloride doped with thioguanine (0.1-1%), strong signals of the radicals associated with thioguanine were observed. For the thymine- thiothymine systems (anhydrous and monohydrate) no characteristic S-centred radicals were observed afterthe same treatment. This Was also the case for samples from non-matching bases and thiols (e.g. cytosine-thioguanine or guanine-thiocytosine), for combinations in the from of frozen glasses or frozen aqueous solutions and for almost all freeze-dried samples composed of the bases containing a small amount of thioanalogues. These observations are discussed in terms of the long-range migration of holes within the stracked base systems.
    Keywords: EPR, free radicals. long-range hole migration, nucleic-acid bases, thioanalog traps

  3. Type of paper: Paper in journal

    Title: Postirradiation long-range energy transfer in a single crystal of cytosine monohydrate: and EPR study

    Authors:
    Sanković, Krešimir (28635)
    Herak, Janko N. (15541)
    Journal: Radiat. Res.
    Volume: 128
    Year: 1991
    Pages: from 119 to 124
    Number of references: 16
    Language: engleski
    Summary: Thiocytosine molecules incorporated in the cytosine monohydrate crystal lattice act as traps for the both electrons and holes. The radiation-induced cytosine ion radicals, C(+) and C(-), release their charge upon heating. The excess electrons and holes migrate long distances in the crystal lattice. The migration of holes has been demonstrated by the postirradiation, thermally activated accumulation of thiocytosine cation radical, T(+), and the migration of electrons by formation of the S-centered radicals of an anionic nature. It is estimated that the migration length of the holes is at least 30 interbase distances, and the migration length of the electrons is more than 100 interbase distances. The selective formation of the cationic and anionic trap radicals, depending on the trap concentration, is discussed in terms of differences between the migration of electrons and holes.
    Keywords: Cytosine monohydrate, electron transfer, EPR, hole transfer, radiation damage

  4. Type of paper: Paper in journal

    Title: EPR evidence for the oxidation-induced formation of negatively charged species on the low-density lipoprotein surface

    Authors:
    Brnjas-Kraljević, Jasminka
    Pifat, Greta
    Herak, Janko N. (15541)
    Jurgens, Gunther
    Journal: Free Rad. Res. Comm.
    Number: 5
    Volume: 14
    Year: 1991
    Pages: from 307 to 313
    Number of references: 21
    Language: engleski
    Summary: Oxidation-induced increase of the net negative charge on low-density lipoprotein was studied by electrophoretic mobility and by electron paramagnetic resonance. The negative-charge increase is associated not only with neutralization of the lysine residues of apoprotein B, but also with the exposition of the excesive negatively charged residues on the lipoprotein surface. The accumulation of the negatively charged residues is believed to be brought about by the conformational change of apoprotein B, triggered by neutralization of lysines and cleavage of peptide bonds. Alternatively, reactive oxygen species could also convert histidine to aspartic acid and proline to glutamic acid.
    Keywords: EPR, LDL, ion binding, lipoprotein oxidation, electrtophoretic mobility

  5. Type of paper: Paper in journal

    Title: The yield of single-strand breaks in double-stranded calf-thymus DNA as a function of OH scavenger concentration: Comparison of experimental data and theoretical results based on nonhomogeneous reaction kinetics

    Authors:
    Udovičić ., Ljiljana (24971)
    Bothe, Eberhard
    Mark, Franz
    Schulte-Frohlinde, Ditrich
    Journal: Period. Biol.
    Number: 2
    Volume: 92
    Year: 1991
    Pages: from 339 to 340
    Number of references: 7
    Language: engleski
    Summary: The yield of the radiation-induced single-strand breaks indouble-stranded DNA was measured. It was shown that the yieldcould be explained on the basis of the non-homogeneous kineticsfor the reaction of the cylindrical surfaces, without the use ofany adjustable parameters. For the systems with rather highconcentration of the scavengers the contribution of OH radicalsto the total yield was about 90%, and the effect of the directaction was about 10%.
    Keywords: Double-stranded DNA, non-homogeneous kinetics single-strand breaks, radiation damage,

  6. Type of paper: Paper in journal

    Title: Oxidation hypothesis of atherogenesis

    Authors:
    Herak, Janko N. (15541)
    Journal: Acta Pharm. Jugosl.
    Volume: 41
    Year: 1991
    Pages: from 299 to 309
    Number of references: 66
    Language: engleski
    Summary: Recent observations indicate that plasma lipoproteins, particulary low-density lipoproteins (LDL), could be modified in vivo. Such modifications, most probably induced by oxidation, could affect their atherosclerotic potential. The physico-chemical nature of the modifications, the arterial environment in which oxidative modification and further fate of LDL take place, and the nature of the oxidative processes have been reviewed. Particular attention has been paid to the possible initation steps. For the first time it has been proposed that besides or instead of the active oxygen species, some other species, residing in the LDL core (depending on diet or environment) could be responsible for initation of the LDL oxidation.
    Keywords: Atherogenesis, initiation of lipoprotein oxidation, LDL

  7. Type of paper: Paper in journal

    Title: Spin traps initiate free radical formation in unsaturated fatty acids

    Authors:
    Herak-Kramberger, Carol Mirna (149081)
    Herak, Janko N. (15541)
    Krilov, Dubravka (23525)
    Journal: Acta Pharm. Jugosl.
    Volume: 41
    Year: 1991
    Pages: from 345 to 350
    Number of references: 16
    Language: engleski
    Summary: Thermally-induced radicals were observed in unsaturated fatty acids incubated with spin traps. Molecular oxygen or peroxides are not required for generation of free radicals. In oxygen-free samples only pure lipid spin aducts are observed. In aerated samples lipid oxy radicals are trapped first. It is concluded that spin traps not only trap formed radicals, but also participate in radical formation reacting with unsaturated fatty acids.
    Keywords: EPR, free radicals, lipid oxidation, unsaturated fatty acids

  8. Type of paper: Paper in journal

    Title: Low-frequency vibrational spectra of cytosine monohydrate single crystals

    Authors:
    Kirin, Davor
    Weber, Igor
    Journal: J. Molec. Structure
    Volume: 267
    Year: 1992
    Pages: from 67 to 72
    Number of references: 12
    Language: engleski
    Summary: Raman scattering measurements were performed on oriented single crystals of cytosine monohydrate (CMH) at frequencies below 400 cm-1. Three previously unreported bands were observed and assigned to translational modes of water molecules. Normal coordinate calculations have been carried out in the rigid-body approximation. Van der Waals and hydrogen bond interactions were taken into account in the atom-atom model potential. The influence of the water-mediated hydrogen-bond network on the lattice dynamics of the CMH crystal is discussed. The implications of this calculation concerning the DNA dynamics are pointed out.
    Keywords: Cytosine monohydrate, Raman scattering, water vibrational modes

  9. Type of paper: Paper in journal

    Title: Chemical modification of low-density liporpotein enhances the number of binding sites for divalent cations

    Authors:
    Pifat, Greta
    Brnjas-Kraljević, Jasminka
    Jurgens, Gunther
    Herak-Kramberger, Carol Mirna (149081)
    Herak, Janko N. (15541)
    Journal: Chem. Phys. Lipids
    Volume: 63
    Year: 1992
    Pages: from 159 to 167
    Number of references: 33
    Language: engleski
    Summary: The EPR technique with paramagnetic Mn(II) ions has been used to probe the negatively charged sites on the surface of modified low-density lipoprotein (LDL). LDL modified in five different ways exhibited increased binding capacity for divalent cations. Enhanced bindig is caused by the increase in the number of 'strong' binding sites. The 'strong' sites have been identified to be the aspartic aci and/or glutamic acid carboxyl residues and 'weak' sites are zwitter-ionic phospholipids. In native LDL the negative groups make 'bonds' with the positive lysyl residues, thus stabilizing the structure. Any deprotonation or modification of the lysine amino groups makes the LDL structure more loose and the amino acid carboxyl groups accessible to divalent cations.
    Keywords: EPR, modified LDL, stabilized structure of LDL, Mn(II) binding

  10. Type of paper: Paper in journal

    Title: Physical changes of low-density lipoprotein on oxidation

    Authors:
    Herak, Janko N. (15541)
    Journal: Chem. Phys. Lipids
    Volume: 66
    Year: 1993
    Pages: from 231 to 234
    Number of references: 28
    Language: engleski
    Summary: Human LDL samples from different individuals were oxidized inthree different ways. All oxidized LDL samples exhibited lowertemperature of the thermotropic transition and lower content ofthe helical fraction of apoprotein B than the related native LDL.The observed decrease of the thermotropic transition temperaturewas up to 2 degrees. The lowering of the transition temperatureis qualitatively explained in terms of the impurity-perturbedmolecular field in the lipid core. The reduction of helicity ofthe apoprotein was drastic: in some samples the helicity wasreduced by more than 50%.
    Keywords: Alpha-helicity, CD, DSC, LDL, oxidation, thermotropic transition

  11. Type of paper: Paper in journal

    Title: Probind of the surface of high-density lipoproteins with Mn(II) ions and EPR spectroscopy

    Authors:
    Brnjas-Kraljević, Jasminka
    Pifat, Greta
    Herak, Janko (15541)
    Journal: Croat. Chem. Acta
    Number: 3
    Volume: 66
    Year: 1993
    Pages: from 550 to 557
    Number of references: 12
    Language: engleski
    Summary: Negatively charged sites on the surface of two human high-densitylipoproteins, HDL2 and HDL3, have been studied using EPRspectroscopy. Like for LDL, there are two types of binding sitesfor Mn(II) ions on each HDL class, characterized by essentiallythe same binding constants as those for LDL. The small number ofamino-acid residues, indicates that only a small fractionof these residues is available for cation binding. The bindingconstants for "weak" sites and the number of these sites in LDLand in the two HDL subfractions studied are consistent with theidea that these sites relate to the phospholipid domains on thelipoprotein surface.
    Keywords: Cation binding, EPR, HDL, surface binding sites.

  12. Type of paper: Ph.D.

    Title: Radiation-induced DNA strand breaks in aqueous solution
    Faculty: Prirodoslovno-matematički Sveučilište u Zagrebu
    Date of defense: 10/15/91
    Language: engleski
    Number of pages: 155
    Summary: Radiation-induced yields of DNA strand breaks in aqueous solutionare investigated both experimentally and theoretically.Experimentally the yields of SSBs and DSBs after irradiation aremeasured by using a low-angle laser light scattering technique.The samples were irradiated under various conditions,particularly varying the concentrations of OH radicals and thescavengers. The yield od SSBs show linear relationship on thedose, while DSBs are formed according to a linear-quadratic doserelationship. The experimental results are compared with thepredictions of the model based on non-homogeneous reactionkinetics. The scavenging dependence of SSBs for single-strandedand double-stranded DNAs is nicely described for cylinder-likemolecules, without adjustment of any of the parameters. Thecalculation shows that even for the highest scavengerconcentrations the greater portion of SSBs arises from theindirect effect. In the oxygen-free systems the role of thesecondary radicals in the SSB formation should not be ignored.The yields of the DSBs in the double-stranded DNA in oxygenetedsolution originates predominantly from the action of OH radicals.
    Keywords: DNA, double-strand breaks, non-homogeneous reaction kinetics, OH radicals, radiation damage, single-strand breaks


  13. Type of paper: M.A.

    Title: Molecular interactions in hydrated crystals of the nucleic-acid bases
    Faculty: Prirodoslovno-matematički Sveučilište u Zagrebu
    Date of defense: 01/01/91
    Language: hrvatski
    Number of pages: 87
    Summary: Raman scattering measurements below 400 cm-1 were performed onoriented single crystals of cytosine monohydrate (CMH) and itsdeuterated analog. Three previously unreported bands wereobserved and assigned to translational modes of water molecules.The lattice dynamics calculations were done treating the cytosineand water molecules as rigid bodies. Intermolecular interactionswere described by summing the atom-atom contributions. Van derWaals and hydrogen bond interactions were taken into account.Five non-equivalent hydrogen bonds were described via tenempirically adjusted force constants. This simple description ofthe force field has been discussed and compared with the moreaccurate theoretical accounts. The eigenvectors of the latticemodes are discussed in detail. The influence of thewater-mediated hydrogen bond network on the lattice dynamics ofthe CMH crystal has been examined. The implications of thecalculation concerning the DNA-dynamics modes are pointed out.
    Keywords: Cytosine monohydrate, Raman spectra, rigid-body approximation, water-molecule vibrations


  14. Type of paper: M.A.

    Title: Dynamics of the lipoprotein oxidation
    Faculty: Prirodoslovno-matematički Sveučilište u Zagrebu
    Date of defense: 12/21/94
    Language: hrvatski


  15. Type of paper: Mentorship

    Title: Radiation-induced DNA strand breaks in aqueous solution
    Faculty: Prirodoslovno-matematički Sveučilište u Zagrebu
    Mentor: HERAK JANKO
    Date of defense: 10/15/91
    Number of pages: 155
    Author: Udovičić Dr. Ljiljana
    Degree level: Ph.D.


  16. Type of paper: Mentorship

    Title: Dynamics of the lipoprotein oxidation
    Faculty: Prirodoslovno-matematički Sveučilište u Zagrebu
    Mentor: HERAK JANKO
    Date of defense: 12/21/94
    Number of pages: 84
    Author: Ukrainczyk Mr. Tatjana
    Degree level: M.A.



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