Go toArchive
Browse byFacets
Bookbag ( 0 )
'Strand Break' in keywords
Results  3 Items
Sorted by   
Publication Year
1988 (1)
1982 (1)
1974 (1)
1Author    Eberhard Bothe, D. Ietrich Schulte-FrohlindeRequires cookie*
 Title    Release of K+ and H+ from Poly U in Aqueous Solution upon y and Electron Irradiation. Rate of Strand Break Formation in Poly U  
 Abstract    Conductivity changes were found which followed the reaction of radiolytically generated OH radicals with the potassium salt of polyuridylic acid (poly U) in aqueous solution. After 60Co-y-irradiation the observed increase of conductivity at pH = 6.8 was shown to consist of the liberation of K+ ions from the stock of K+ ions electrostatically bound to the polyanion. The initial G(K+) is 36 and hence 6 times higher than the G value of OH radicals in N20 saturated solutions. At a poly U concentration of 60 mg I-1 half of the ion release occurred at 12 J kg-1 and nearly all ions are released at 40 J kg-1. The liberation of K+ is explained to be a consequence of the formation of chain breaks leading to an increase of the degree of dissociation. The rate of the ion release was studied under pulse radiolysis conditions. Because of the high G-vlaue of counterion liberation and the use of conductivity as analytical quantity the method is very sensitive. With 6 mg I-1 poly U the rate could be measured even at a dose per pulse of 0.25 J kg-1. The kinetics of the ion release can be described in terms of two parallel first order reactions of comparable contribution with an average rate constant of 0.8 s-i at 20 °C, 60 mg l-1 poly U and pH = 6.8 with a small contribution of slower components. In more acidic solutions, besides K+ ions H+ are also liberated since at low pH values bound K+ is replaced by H+. The rate of the ion release was found to increase with increasing replacement of K+ by H+ (^?bs = 100 s-1 at pH = 3.4, 60 mg I-1 poly U and T = 18 °C). With potassium ion free poly­ uridylic acid the corresponding rate constant amounted to 220 s_1, nearly independent of pH. From the temperature dependence activation parameters for the ion release were derived (£ a = 57 kJ mol-1, A = 1.0 x 1010 s— 1 at pH = 6.8). Addition of p-benzoquinone at pH = 3.7 and dithiothreitol (DTT) at pH 6.8 were found to decrease the size of the conductivity changes and to increase the rate. The results show that p-benzoquinone and DTT react with poly U radicals and that these reactions prevent chain breaks and ion liberation. It is concluded that the rate determining step of the conductivity increase is the formation of strand breaks by a cleavage of poly U radicals and that this reaction is pH dependent. The pH dependence and the observed value for the activation energy was found to be in agreement with the behaviour of a model system for the earlier postulated C-4' mechanism for strand break formation of polynucleotides and DNA. 
  Reference    Z. Naturforsch. 37c, 1191—1204 (1982); received July 5 1982 
  Published    1982 
  Keywords    Polyuridylic Acid, Irradiation, Conductivity, Strand Break, Rate 
  Similar Items    Find
 TEI-XML for    default:Reihe_C/37/ZNC-1982-37c-1191.pdf 
 Identifier    ZNC-1982-37c-1191 
 Volume    37 
2Author    CherlaP. Murthy, DavidJ. Deeble, Clemens Von SonntagRequires cookie*
 Title    The Formation of Phosphate End Groups in the Radiolysis of Polynucleotides in Aqueous Solution  
 Abstract    The polynucleotides poly(U), poly(C), poly(A) and poly(G) have been y-irradiated in N20-and N20/02 (4:l)-saturated aqueous solutions. Hydroxyl radicals from the radiolysis of water react with the polynucleotides thereby producing among other lesions strand breaks. Strand break-age is connected with the formation of phosphomonoester end groups. Such end groups have been determined by measuring inorganic phosphate after a three hour incubation at 37 °C with acid or alkaline phosphatase. In the absence of oxygen G(phosphomonoester end groups) (in units of i^mol J' 1) are 0.47 (poly(U)), 0.17 (poly(C)) and < 0.04 (poly(A) and poly(G)). In the case of poly(U) and poly(C) on heating the sample for one hour at 95 °C prior to incubation with phosphatases the above values increased by 0.14 and 0.07 jxmol J" 1 , resp., whereas such treatment of the purine poly-nucleotides still did not produce a measurable yield of phosphomonoester end groups. Comparing these values with G values for strand breakage taken from the literature, about two phospho-monoester end groups are formed per strand break in poly(U) while for poly(C) this ratio is about unity. The purine polynucleotides show very low yields of strand breakage in agreement with the negligible phosphomonoester yields. In the presence of oxygen G(phosphomonoester end groups) are 0.46 (poly(U)), 0.21 (poly(C)), and < 0.04 (poly(A) and poly(G)). On heating, these values increase, most markedly for poly(U) and poly(C). This is possibly linked to the decomposition of unstable hydroperoxides which are formed in high yields in poly(U) and poly(C) (G = 0.7 and 0.19 nmol J resp.). It is known that at least in the case of poly(U), base radicals attack a sugar moiety and are the main precursors of these lesions. G(phosphomonoester end groups) are considerably lower in the case of the purine polynucleotides. Whether this is due to an inability of the base radicals to attack a sugar moiety or has other reasons must remain an open question. 
  Reference    Z. Naturforsch. 43c, 572—576 (1988); received March 14 1988 
  Published    1988 
  Keywords    Polynucleotides, Strand Break, Phosphomonoester End Group, Oxygen Effect 
  Similar Items    Find
 TEI-XML for    default:Reihe_C/43/ZNC-1988-43c-0572.pdf 
 Identifier    ZNC-1988-43c-0572 
 Volume    43 
3Author    Wolfgang KöhnleinRequires cookie*
 Title    The Influence of Hydrogen Donors on Breakage of Parental DNA Strands and on Biological Activity of Transforming BrU-DNA of B. subtilis after 302/313 nm Radiation  
 Abstract    Long wavelength UV irradiation (302/313 nm) of hybrid and bifilarly labeled BrU-DNA of B. subtilis results in a degradation of the molecular weight of BrU and of parental thymine con­ taining DNA strands. Hydrogen donors present during UV irradiation are able to prevent these "primary" and "secondary" strand breaks. The protection factors are especially large for secondary breaks in parental normal DNA. Through the action of protective agents the biological activity could not be restored. The generation of these primary and secondary strand breaks due to BrU incorporation and the action of hydrogen donors discussed. 
  Reference    (Z. Naturforsch. 29c, 66 [1974]; received October 3/November 23 1973) 
  Published    1974 
  Keywords    BrU-DNA, Hydrogen-Donors, Strand Breaks, Transforming Activity, Radiation 
  Similar Items    Find
 TEI-XML for    default:Reihe_C/29/ZNC-1974-29c-0066.pdf 
 Identifier    ZNC-1974-29c-0066 
 Volume    29