W. Wang et Md. Sevilla, REACTION OF CYSTEAMINE WITH INDIVIDUAL DNA-BASE RADICALS IN GAMMA-IRRADIATED NUCLEOTIDES AT LOW-TEMPERATURE, International journal of radiation biology, 66(6), 1994, pp. 683-695
Citations number
49
Categorie Soggetti
Radiology,Nuclear Medicine & Medical Imaging","Nuclear Sciences & Tecnology
An ESR investigation of the individual DNA base radicals produced by g
amma-irradiation of frozen solutions of the nucleotides TMP, dCMP, dGM
P and dAMP and their reactions with cysteamine upon annealing is repor
ted. The results show that water radicals in bulk ice do not lead to t
he formation of DNA or cysteamine radicals. Radicals from the oxidatio
n pathway which include the DNA base one electron oxidized radicals an
d their successors, G(C8)OH., A(C8)OH. and thymine dimers (T-.(dl)) an
d/or T(C6)OH., readily react with cysteamine to form RS' and ultimatel
y RSSR(-.) Reactions of dGMP and dCMP radicals from the oxidation path
way with cysteamine occur at lower temperatures than those of dAMP and
TMP, suggesting hole migration. Both T(C6)H-. and C(N3)H-. react with
cysteamine to form RS' and diamagnetic products, but G(C8)H-. and A(C
8)H-. do not. Subtraction of the anion radical T--. and its proton add
uct T(C6)H-. from the total radical yield of TMP (with or without cyst
eamine) suggests that somewhat less than half of the total TMP radical
s found are a result of the oxidative pathway. Similar results are fou
nd in the other nucleotides. The total spectral intensity derived fi o
m the radicals from the oxidative pathway such as G(C8)OH., A(C8)OH. a
nd T-.(di)/T(C6)OH. are somewhat less than that for the protonated ani
on radicals. Only one non-base radical is identified, a sugar radical
at the C(1)' site on the deoxyribose portion of dAMP. This species, S(
A)(.), is also found to react with cysteamine or its disulfide radical
anion. Analyses performed in the presence and absence of a thiol are
found to allow for a clear separation of oxidative and reductive pathw
ays.