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J D Zimbrick

Publications and source records attributed to J D Zimbrick.

At least 19 recordsLinked to original sources
PubMed1995

Radiation chemistry of d(ApCpGpT).

The radiation chemistry of the DNA tetranucleoside triphosphate d(ApCpGpT) was investigated. Irradiations were carried out on aqueous solutions saturated with oxygen (with and without added Cu++), nitrogen or nitrous oxide. When oxygen was present, principal products were formed by hydroxylation at the 8-position of guanine and by degradation of thymine leaving a formamido remnant. Products were also formed containing both of the aforementioned lesions at adjacent deoxyguanosine and pyrimidine nucleosides. Other products resulted from rearrangement of the thymine ring generating two diastereoisomers of the 5-methyl-5-hydroxyhydantoin modification of d(ApCpGpT). Rearrangement of the cytosine ring occurred generating imidazolidine products and a hydantoin product. The product profiles are similar when either an N2O or N2 gaseous environment is maintained. However, in the latter case the dihydrothymine modifications of d(ApCpGpT) are markedly enhanced. Other products include an 8,5' cyclized product formed from the 2'-deoxyadenosine nucleoside and the 8-hydroxyguanine modification. 6-Hydroxy-5,6-dihydrothymine and 5,6-dihydroxy-5,6-dihydrothymine modifications of the thymidine nucleoside were also observed. A strand break product formed in oxygenated solution is also produced in nitrous oxide saturated solutions. Scission of the deoxyadenosine terminus was also observed. The effect of several of these lesions on d(ApCpGpT) as substrate for nuclease P1, bovine spleen phosphodiesterase and snake venom phosphodiesterase was studied.

Oligodeoxyribonucleotides↗
PubMed1994

Electron migration in oligonucleotides upon gamma-irradiation in solution.

Electron migration in irradiated solutions of DNA was investigated using 5-bromouracil synthetically incorporated into oligonucleotides of defined base composition as a molecular indicator of electron interactions. Solvated electrons interact quantitatively with 5-bromouracil, leading to a highly reactive 5-yl radical which can abstract an adjacent hydrogen atom to yield uracil. Yields of uracil, or loss of 5-bromouracil, from irradiated oligonucleotide samples were measured using gas chromatography-mass spectrometric analysis of their trimethylsilylated acid hydrolysates. To examine the effects of base composition and DNA conformation on electron migration, a set of oligonucleotides containing 5-bromouracil at selected positions with three base (guanine, cytosine, thymine or adenine) spacers (e.g. [BrU(GGG)3]3) were irradiated in their single- or double-stranded form following annealing with appropriate complementary sequences. Differences in uracil yields suggested that electron migration occurred to different extents in oligonucleotides containing different base sequences. In irradiated single-stranded oligonucleotides, the yield of uracil decreased in the order A > T > > C approximately G. However, in irradiated double-stranded oligonucleotides, the yield of uracil decreased in the order G > C approximately T > A. These differences were attributed to proton-transfer reactions facilitated by base pairing in double-stranded oligonucleotides. The distance over which the electron would migrate was then determined using a series of oligonucleotides containing 5-bromouracil at selected positions with guanine spacers (i.e. [BrU(G)n]3 (n = 3, 5, 7, 9). Oligonucleotides were irradiated in their double-stranded form following annealing with the appropriate complementary sequences. Analysis of the loss of 5-bromouracil revealed that electron migration occurred efficiently over c. 3-4 guanine bases assuming that migration could occur as efficiently in either direction along the DNA molecule. These data can be compared with studies reporting more extensive migration for electrons generated by direct ionization of DNA.

Base Sequence↗
PubMed1994

Radiation-induced electron migration in nucleic acids.

Radiation-induced electron migration along DNA is a mechanism by which randomly produced stochastic energy deposition events can lead to non-random types of damage along DNA manifested distal to the sites of the initial energy deposition. Radiation-induced electron migration in nucleic acids has been examined using oligonucleotides containing 5-bromouracil (5-BrU). Interaction of 5-BrU with solvated electrons results in release of bromide ions and formation or uracil-5-yl radicals. Monitoring either bromide ion release or uracil formation provides an opportunity to study electron migration processes in model nucleic acid systems. Using this approach we have discovered that electron migration along oligonucleotides is significantly influenced by the base sequence and strandedness. Migration along 7 base pairs in oligonucleotides containing guanine bases was observed for oligonucleotides irradiated in solution, which compares with mean migration distances of 6-10 bp for Escherichia coli DNA irradiated in solution and 5.5 bp for E. coli DNA irradiated in cells. Evidence also suggests that electron migration can occur preferentially in the 5' to 3' direction along a double-stranded oligonucleotide containing a region of purine bases adjacent to the 5-BrU moiety. Our continued efforts will provide information regarding the contribution of electron transfer along DNA to formation of locally multiply damaged sites created in DNA by exposure to ionizing radiation.

Base Sequence↗
PubMed1994

Electron migration along 5-bromouracil-substituted DNA irradiated in solution and in cells.

Solvated electrons generated in aqueous solution after exposure to ionizing radiation can be scavenged by DNA and then transferred along the DNA molecule. This mechanism of charge transfer provides an opportunity for radiation damage to be targeted to certain regions in the DNA molecule and is a mechanism by which single-strand breaks contribute to locally multiply damaged sites to enhance cell lethality. Experiments were performed in which different amounts of 5-bromouracil (5-BrU) were substituted for thymine in Escherichia coli DNA. The amount of bromide released was assayed after quantitative reaction of radiation-induced solvated electrons with 5-BrU in DNA samples irradiated in solution and irradiated in the cellular environment. By varying the amount of 5-BrU incorporated in the DNA, the average distance between 5-BrU molecules was systematically changed and, because the number of 5-BrU/electron reactions was monitored by the amount of bromine released, the maximum average electron migration distance along the 5-BrU DNA could be estimated. Using this approach, the maximum average electron migration distance in aqueous solutions of 5-BrU DNA was about 6.5 to 10 base distances in nonhybrid 5-BrU DNA (assuming only intrastrand migration). Similar methods revealed charge migration in 5-BrU DNA incorporated into E. coli, and the maximum average migration distance was about 5 to 6 base distances (assuming only intrastrand migration). Only 11-16% of the electrons produced during radiolysis were scavenged by 5-BrU DNA in aqueous solution, and only 1% resulted in the release of bromide from 5-BrU-DNA inside E. coli.

Bromouracil↗
PubMed1986

PDN-1: a spin-labeled analog of cis-diamminedichloroplatinum(II). Biophysical studies in aqueous, lipophilic, and biological media.

Biophysical and biochemical studies on a biradical-labeled analog of Cisplatin, PDN-1, in aqueous, biological, and lipophilic media are presented. The ESR spectra from PDN-1 in aqueous meida show five-line spectra typical of biradicals in which intramolecular spin exchange occurs. The spectrum of PDN-1 in 1-octanol is characterized by three broad lines overlying a fourth line that is approximately three times as wide as the others. Although the characteristics of the aqueous spectra differ substantially from those of the octanol spectra, both the midfield peak height and the integral of the absorption spectrum can be used as a linear measure of PDN-1 concentration in either media. The smallest concentration used in these linear calibrations was equivalent to the detection of 60 femptomoles of PDN-1 at a signal-to-noise ratio of 30. PDN-1 is shown to "decay" in tissue culture medium which involves either the reduction of a nitroxyl moiety, the labilization of an amino bond, or a combination of both. Spectra of intracellular PDN-1 show that both a mobile ("free") fraction and slowly tumbling ("bound") fraction of the compound can be detected within CHO cells. The spin-labeled cisplatin method is at least as sensitive as conventional chromatographic and spectroscopic methods, yet has the added advantage of offering information about the molecular environment of the complex.

Animals↗
PubMed1986

Spin-label substitutions in cisplatin reduce toxicity and interaction with radiation.

A piperidinyl-labeled platinum(II) complex, cis-Pt[2,2,6,6-tetramethyl-4-aminopiperidine-N-oxyl]2dichloride , is an ESR-traceable analog of the antitumor agent, cis-diamminedichloroplatinum(II), DDP. The toxicity of the analog (PDN-1) in Chinese hamster ovary (CHO) cells is 22 times less than that of the parent compound: D0 (where D0 = slope-1 of the straight-line portion of the survival curve) = 0.11 mM versus 0.0053 mM for 1.5-h treatments with PDN-1 and DDP, respectively. At PDN-1 doses that cause 10% killing when used alone, no statistically significant increase in cell killing of hypoxic, irradiated cells was observed. PDN-1 does not have significant dose-modifying properties but may be a useful probe to study platinum in mammalian cells.

Animals↗
PubMed1983

Ethanol effects on synaptic glutamate receptor function and on membrane lipid organization.

The enhancement of L-glutamic acid binding activity of brain synaptic membranes by low concentrations of ethanol (less than 50 mM) and the decrease in binding at high concentrations (greater than 100 mM) was not due to a direct action by ethanol on the glutamate binding protein. Biphasic effects of ethanol on membrane protein complexes such as the glutamate binding sites might be the result of biphasic changes in membrane lipid organization. Low ethanol concentrations (0.1-4.0 mM) were shown to decrease fatty acid chain motion detected by the EPR probe 5-doxyl stearic acid, whereas high concentrations (greater than 400 mM) increased lipid motion in egg phosphatidylcholine liposomes. The function of the L-glutamate receptor-ion channel complex in the presence of ethanol was also determined by measuring the changes in thiocyanate (SCN-) influx brought about by L-glutamate or ethanol. A low concentration of ethanol (9.4 mM) diminished the L-glutamate-induced depolarization of synaptic membranes, while a high concentration (93.7 mM) increased the passive SCN-influx and produced a transient overshoot in glutamate-stimulated SCN-flux.

Animals↗
PubMed1982

Spin trapping of reactive uracilyl radicals produced by ionizing radiation in aqueous solutions.

The DNA base analogue 5-bromouracil (BU) reacts with hydrated electrons to produce a highly reactive uracil-5-yl (uracilyl) radical. The uracilyl radical was spin trapped by 5,5-dimethylpyrroline-1-oxide (DMPO) and t-nitrosobutane (tNB). DMPO solutions (0.01 M at pH = 7, N2 or N2O saturated) without BU were irradiated with 60Co gamma-rays and the resulting spin adducts produced by e-aq, H., and OH. were identified. The irradiation of alkaline (pH 12, N2 saturated) solutions of DMPO alone simplified the e.p.r. spectrum of spin adducts in that only the H. adduct was observed. Irradiated DMPO solutions (pH 12, N2 saturated) containing BU yielded a composite of two six-line e.p.r. spectra, attributed to uracilyl spin adducts that have two distinct steric configurations, and a background spectrum of H.-DMPO adducts which was removed by computer-subtraction. Uracilyl-tNB spin adducts were detected by first trapping uracilyl radicals in irradiated photobleached 10 M NaOH glasses at 77 K and then dissolving these glasses in pH-adjusted tNB solutions.

Bromouracil↗
PubMed1980

Ethanol effects on synaptic glutamate receptors and on liposomal membrane structure.

Exposure of synaptic plasma membranes to 50 mM ethanol in vitro brought about a 3.5 degrees C decrease in the transition temperature of the high affinity glutamate binding process in these membranes. Ethanol had no effect on the energy of activation of glutamate binding below the transition temperature but decreased the energy of activation above the transition temperature. Electron paramagnetic resonance (EPR) studies of lipid organization of egg lecithin and bovine brain phospholipid liposomes indicated that ethanol at low concentrations (0.04--2 mM) caused small increases in the rigidity of the membrane near the surface. At higher concentrations (0.04--2 M) ethanol brought about increasing fluidization of both the surface and inner areas of the bilayer. Even at 4 mM concentration ethanol enhanced the ordered to fluid state transition of liposome membranes as shown by a 5.2 degrees C and 1.9 degrees C decrease in the transition temperatures of the membrane determined with the cholestane EPR probe.

Animals↗
PubMed1979

Electron spin resonance studies on properties of ceruloplasmin and transferrin in blood from normal human subjects and cancer patients.

The methodology of blood sample preparation and analysis has been examined to further evaluate the technique of electron spin resonance (ESR) for possible use in detecting cancer and in monitoring the progress of cancer therapy. Frozen whole blood and serum samples from 278 normal donors and 97 cancer patients were studied by ESR for signal intensity from Cu+2 bound to ceruloplasmin (g factor = 2.05). The signal from this species (Cu+2-CP) in serum rose sharply during the first two hours of storage at room temperature after being drawn from the subject, and then reached a plateau. The average Cu+2-CP ESR signal intensity was significantly different for control groups of males, females not taking estrogen medication, and females taking estrogens. The mean ESR signal intensities of Cu+2-CP from cancer patients separated into the same groups as the control data were approximately twice as great as the mean control levels. Total serum copper levels were correlated with ESR intensities of Cu+2-CP and indicated that the ratio of Cu+2/Cu+1 in CP is higher in serum from cancer patients than from controls.

Age Factors↗
PubMed1975

E.s.r. studies of halogenated pyrimidines in gamma-irradiated alkaline glasses.

The reactions of mobile electrons (em-) and oxygen radical anions (O--) with halogenated bases and nucleosides have been studies in gamma-irradiated alkaline glasses by e.s.r. and specific halogen-ion electrode techniques. It is shown that electrons react with halogenated uracil bases (XUr where X = Cl, Br. I but not F) by dissociative electron attachment to form uracil-5-yl radicals (U-) and halogen anions. The relative rates of reaction of em- with XUr decrease in the sequence BrUr greater than ClUr greater than FUr greater than IUr. Thermal annealing studies carried out on U- in H2O and D2O matrices support the hypothesis that U- in H2O hydrates across the 5-6 double bond in the temperature region 135 degrees-155 degrees K, and deuterates to a much smaller extent in D2O at temperatures above 155 degrees K. Studies on bromouridine and bromodeoxyurinde suggest that em- reacts with the base moieties to form U- type radicals which abstract H- from the sugar moieties of adjacent nucleosides.

Bromouracil↗