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BY-NC-ND 3.0 license Open Access Published by De Gruyter June 2, 2014

The Formation of Phosphate End Groups in the Radiolysis of Polynucleotides in Aqueous Solution

  • Cherla P. Murthy , David J. Deeble and Clemens von Sonntag

The polynucleotides poly(U), poly(C), poly(A) and poly(G) have been y-irradiated in N2O- and N2O/O2 (4:1)-saturated aqueous solutions. Hydroxyl radicals from the radiolysis of water react with the polynucleotides thereby producing among other lesions strand breaks. Strand breakage 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 μmol 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 μmol J-1, resp., whereas such treatment of the purine polynucleotides 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 phosphomonoester 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 μmol J-1 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.

Received: 1988-3-14
Published Online: 2014-6-2
Published in Print: 1988-8-1

© 1946 – 2014: Verlag der Zeitschrift für Naturforschung

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