- 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
- 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
- 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
- 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
- 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,
- 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
- 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
- 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
- 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
- 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
- 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.
- 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
- 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
- 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
- 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.
- 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.