GENERATION OF 5,5-DIMETHYL-1-PYRROLINE N-OXIDE HYDROXYL AND SCAVENGERRADICAL ADDUCTS FROM COPPER H2O2 MIXTURES - EFFECTS OF METAL-ION CHELATION AND THE SEARCH FOR HIGH-VALENT METAL-OXYGEN INTERMEDIATES/
Mj. Burkitt et al., GENERATION OF 5,5-DIMETHYL-1-PYRROLINE N-OXIDE HYDROXYL AND SCAVENGERRADICAL ADDUCTS FROM COPPER H2O2 MIXTURES - EFFECTS OF METAL-ION CHELATION AND THE SEARCH FOR HIGH-VALENT METAL-OXYGEN INTERMEDIATES/, Archives of biochemistry and biophysics, 323(1), 1995, pp. 63-70
A metal-catalyzed nucleophilic addition mechanism for the formation of
radical adducts of the spin trap 5,5-dimethyl-1-pyrroline N-oxide (DM
PO) has been described recently (It. Makino, T. Hagiwara, A Hagi, M. N
ishi, and A Murakami, 1990, Biochem. Biophys. Res. Commun. 172, 1073-1
080; P. M. Hanna, W. Chamulitrat, and R. P. Mason, 1992, Arch. Biochem
. Biophys. 296, 640-644). In the present investigation, we have demons
trated that the recently reported inhibition of copper-dependent hydro
xyl radical formation by the complexing agent 1,10-phenanthroline (OP)
, which appears to contradict the well-known chemical nuclease propert
ies of Cu-I(OP)(2), is an artifact resulting from an inhibition of the
nucleophilic addition of water to DMPO by OP (A C. Mello-Filho and R.
Meneghini, 1991, Mutat. Res. 251, 109-113). Copper bound to OP was fo
und to be a good catalyst of hydroxyl radical formation: the Cu-II(OP)
(2) complex can be reduced by H2O2 and the Cu-(I)(OP)(2) generated rea
cts with the peroxide to form (OH)-O-.. In contrast, no evidence could
be obtained for oxidant formation from the Cu-(aq(II))/H2O2 reaction
system, despite the detection of a prominent signal from the DMPO hydr
oxyl radical adduct (DMPO/(OH)-O-.) (the formation of which was due so
lely to the nucleophilic addition of water to DMPO). The failure to ge
nerate an oxidant in this reaction mixture was attributed to the failu
re of hydrogen peroxide to reduce Cu-(aq(II)), as hydroxyl radical for
mation did occur when Cu-(aq(I)) was added directly to H2O2. However,
in order to account for the high concentration of alpha-hydroxyethanol
radicals detected when ethanol was included in the Cu-(aq(I))/H2O2 re
action, the possibility that an oxidant in addition to (OH)-O-. (e.g.,
CuO+) is generated is discussed. (C) 1995 Academic Press, Inc.