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Dégradation du DNA par H 2 O 2 en présence d'ions Cu ++ , Fe ++ et Fe +++
Author(s) -
Schweitz H.
Publication year - 1969
Publication title -
biopolymers
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.556
H-Index - 125
eISSN - 1097-0282
pISSN - 0006-3525
DOI - 10.1002/bip.1969.360080109
Subject(s) - chemistry , ion , dna , degradation (telecommunications) , molecule , crystallography , analytical chemistry (journal) , chromatography , organic chemistry , telecommunications , biochemistry , computer science
The mechanism of degradation of calf thymus DNA by H 2 O 2 in dark and light, and in the presence of either Cu ++ , Fe ++ , or Fe +++ ions has been investigated by following the decrease of molecular weight M̄ w by light scattering. Both in the dark and in light, the rate of degradation decreases in the following order: Cu ++ >Fe ++ >Fe +++ . In order to exploit quantitatively the variation of M̄ w with time, we calculated the probability p ( t ) of rupture in a double stranded polymer as a function of the occurence at random of both breaks of the “first kind” (single hits) and of the “second kind” (double hits), when there are caused by any degrading agent. The value of p ( t ) can then be related to M̄ w ( t ) for the present case of a randomly polydisperse sample of DNA molecules. In the dark, and in the presence of Cu ++ ions, a degradation of the first kind (which takes place through the simultaneous or successive splitting of both strands of DNA at the same level) is the only one so far observed. The number of degradation sites of the first kind is equivalent to the number of bound Cu ++ ions in inner sites of DNA. A model is set up to explain the successive breaks of the two strands of the DNA molecule through the formation of a complex (DNA site–Cu ++ ‐H 2 O 2 ) which exhibits peroxidative properties. The comparison of the degradation induced under these conditions in a native and a sonicated DNA, shows that the specific sites of attack of ultrasonic waves are not specific sites of H 2 O 2 action in the presence of Cu ++ ions. In the dark and in the presence of Fe ++ or Fe +++ ions, breaks of the first kind and second kind are superimposed, but the last are predominant. This is ascribed to the low binding of iron ions in inner sites of DNA under these conditions. A large increase in degradation rate of the second kind occurred in the presence of light (with or without added metallic ions and) is ascribed to the action of the free radicals HO · (and HO 2 · ) which arise from the photolysis of H 2 O 2 . These results are discussed in relation to those obtained by the action of ionizing radiations on aqueous solutions of DNA.