Jewett, SL, Rocklin,
AM, Ghanevati, M, Marach,
JA, and Abel,
JM (1999). Free Rad. Biol. Med. 26(7): 905-918.
A New Look at a Time-Worn System: Reaction of CuZnSOD
with H2O2
ABSTRACT
This work summarizes observations from numerous investigators
on the reaction of the copper-zinc superoxide dismutase with hydrogen peroxide
at physiological pH in order to propose a likely sequence of events that
leads to 2-oxo-histidine formation, copper loss, inactivation, and random
and site-specific peptide fragmentation. New data is presented for
the bovine liver enzyme that indicate copper is lost as the copper(I) form
which immediately reacts with bathocuproine disulfonate to form the characteristic
complex that absorbs at 485 nm. Studies in TRIS buffer ruled out
the loss of copper(II) followed by reduction of the high potential copper(II)-bathocuproine
disulfonate complex by buffer because TRIS is known not to reduce this
complex. The rate of loss of copper(I) is not affected by the spin trap,
5,5-dimethylpyrolline-N-oxide (DMPO), nor by replacing oxygen with argon
in the reaction. In addition, changes in the native electrophoretic
pattern that are correlated with copper loss and not peptide fragmentation
are also unaffected by DMPO, argon, EDTA, or DTPA. These data are
taken as indirect evidence that the formation of 2-oxo-histidine is the
first oxidative event, unaffected by DMPO, that occurs at the bound oxidant
and leads to loss of copper(I). Peptide fragmentation and the peroxidative
activity of the dismutase are discussed in light of these observations.