24 Matching Results

Search Results

Advanced search parameters have been applied.

Mechanisms for radiation damage in DNA. Progress report, June 1, 1973-- May 31, 1974

Description: A mechnnism has been proposed for radiation damage to DNA and a series of experiments detailed utilizing electron spin resonance spectrometry to test the proposed mechanism. Thus far we have produced and investigated the positive and negative ions of a number of purine and pyrimidine DNA bases in aqueous glasses. The g values and hyperfine couplings, both anisotropic and isotropic, have been determined when possible. The 5-methyl substituted pyrimidine cations (thymine, thymidine, 5-methylcytosine and 5-methylcytidine) react in these aqueous systems by deprotonation of the 5-methyl group. The thymine anion has been found to protonate in neutral aqueous glasses. Investigations of the cation and anion radicals of the other DNA bases have shown a lessened tendency toward further reaction. In related work the reactions of electrons with 5-halouracils as well as amino acids and peptides were studied. In work with 5-halouracils we have isolated the anions, found their relative stability, and followed their further reactions. Results were in agreement with those of other experimental methods. (auth)
Date: January 1, 1974
Creator: Sevilla, M.D.
Partner: UNT Libraries Government Documents Department

Chemical and biological studies on nucleic acids and derivatives. Progress report, October 1, 1974--April 30, 1975

Description: Ultraviolet irradiation of N-hydroxyxanthines in the solid state induces a radical that was assigned as an acyl amidogen radical in which the unpaired electron density is partially delocalized throughout the $pi$-cloud of the purine ring. The radical is reduced in the presence of water. In the presence of methanol this process is also accompanied by some 8-substitution. Photochemical deoxygenation in solution was found to proceed from either the nonionized N- hydroxyl tautomer or the conjugate anion of N-hydroxypurines. Reduction is the sole photoreaction of the former, while intramolecular migration of the oxygen is the main photoprocess of the latter with photoreduction a minor result. The comparison of the photochemistry of the N-hydroxypurine anion to that of the corresponding purine N-oxide was documented with a study of suitable model purine 1-oxides. A unique photorearrangement of 1-hydroxyxanthine to the oncogenic 3- isomer was examined and is deduced to be a two step process. (auth)
Date: October 1, 1975
Creator: Brown, G.B.
Partner: UNT Libraries Government Documents Department

DNA damage in mammalian cells and its relevance to lethality

Description: From fourth symposium on microdosimetry; Pallanza, Italy (24 Sep 1973). Cell killing (loss of proliferative capacity) is a principal end point in all radiation effects contingent upon cell viability. DNA, the molecular carrier of the genetic inheritance, affects the affairs of a cell because the properties and characteristics of a cell are dictated by the DNA -- RNA -- protein axis of information storage, flow, and expression. Thus, the mutagenic and chromosome- breaking properties of radiation, the biological amplification available to a lesion in DNA, and the fact that DNA molecularly constitutes a very large radiation target, aH make DNA the principal target relative to many radiation effects. An indirect approach may be useful in studies of the sensitive targets in a mammalian cell. This stems from the fact that to kill cells with low LET radiation; sublethal damage must be accumulated and cells can repair this damage. Thus, focussing on DNA, and repair processes in DNA, while indirect, is supporied in the instance of cell killing by extensive experimental evidence. The status of damage registered directly in DNA may be assessed by examining changes in the sedimentation of DNA from irradiated cells. Along with measurements of cell survival, sedimentation data are discussed relative to their bearing on cell killing and their ability to help us understand the organization and replication of DNA in mammalian cells. (CH)
Date: January 1, 1973
Creator: Elkind, M.M. & Ben-Hur, E.
Partner: UNT Libraries Government Documents Department

Molecular dosimetry of chemical mutagens: measurement of molecular dose and DNA repair germ cells

Description: Molecular dosimetry in the germ cells of male mice is reviewed with regard to in vivo alkylation of sperm heads, in vivo alkylation of sperm DNA, and possible alkylation of sperm protamine. DNA repair in male germ cells is reviewed with regard to basic design of experiments, DNA repair in various stages of spermatogenesis, effect of protamine on DNA repair following treatment with EMS or x radiation, and induction of DNA repair by methyl methanesulfonate, propyl methanesulfonate, and isopropyl methanesulfonate. (HLW)
Date: January 1, 1975
Creator: Sega, G.A.
Partner: UNT Libraries Government Documents Department

Effect of radiation on proteins and radiation effects in biochemistry and organic chemistry. Final report, October 15, 1957--October 14, 1974

Description: A summary is made of a fifteen year study of chemical effects of radiation of amino acids and proteins. Included is a list of publications: 54 papers, reports and abstracts, and 10 M.S. and Ph.D theses. The report concludes with details of the final two studies done under this contract. These are, first, a study of post-irradiation effects of various gases on gamma irradiated lysozyme. This study showed that H$sub 2$S, O$sub 2$, NO, and N$sub 2$O treatment changed the amount of aggregation products, and also that a certain amount of the irradiated lysozyme was subject to main chain cleavage. The second was a study of proteins in rabbit eye lens cataracts induced by x-irradiation or a high galactose diet. The cataract proteins were more soluble in water than normal proteins, and were present in lower amounts in the eye lens. (auth)
Date: January 1, 1974
Creator: Tolbert, B.M.
Partner: UNT Libraries Government Documents Department