Si. Liochev et I. Fridovich, On the role of bicarbonate in peroxidations catalyzed by Cu,Zn superoxide dismutase, FREE RAD B, 27(11-12), 1999, pp. 1444-1447
The interaction of Cu,ZnSOD with H2O2 generates an oxidant at the active si
te that can then cause either the inactivation of this enzyme or the oxidat
ion of a variety of exogenous substrates. We show that the rate of inactiva
tion, imposed by 10-mM H2O2 at 25 degrees C and pH 7.2, is not influenced b
y 10-mM HCO3-; whereas the oxidation of 2,2'-azino-bis-[3-ethylbenzothiazol
ine sulfonate] (ABTS(=)) is virtually completely dependent upon HCO3-. The
reduction of the active site Cu(II) by H2O2, which precedes inactivation of
the enzyme, occurred at the same rate in phosphate buffer with or without
bicarbonate added. These results indicate that HCO3- does not play a role i
n facilitating the interaction of H2O2 with the active site copper, but the
y can be accommodated by the proposal that HCO3- is oxidized to HCO3., whic
h then diffuses from that site and causes the oxidation of substrates, such
as ABTS(=), that are too large to traverse the solvent access channel to t
he Cu(II). (C) 1999 Elsevier Science Inc.