当前位置： SCI文献检索 > ARCHIVES OF BIOCHEMISTRY AND BIOPHYSICS期刊下所有文献 > Reaction mechanism of electron transfer from FeII(CN)6(4-) or W(IV)(CN)8(4-) to the cupric ions in human copper, zinc superoxide dismutase.

Reaction mechanism of electron transfer from FeII(CN)6(4-) or W(IV)(CN)8(4-) to the cupric ions in human copper, zinc superoxide dismutase.

Abstract：

:The electron transfer reactions from FeII(CN)6(4-) and W(IV)(CN)8(4-) to the cupric ions in human copper, zinc superoxide dismutase were followed by the micro-stopped-flow method. The kinetic rate data clearly indicate that FeII(CN)6(4-) or W(IV)(CN)8(4-) first forms an adduct with the enzyme through the interaction with Arg143 of the active cavity and then an electron from FeII(CN)6(4-) or W(IV)(CN)8(4-) of the adduct transfers to the cupric ion in the enzyme. The dissociation constants of the adducts of FeII(CN)6(4-) and W(IV)(CN)8(4-) were 4.0(+/-0.3) x 10(-3) and 2.2(+/-0.3) x 10(-3) M, respectively. In spite of the difference between the standard redox potentials of FeIII(CN)6(3-)/FeII(CN)6(4-) (468 mV) and W(V)(CN)8(3-)/W(IV)(CN)8(4-) (556 mV), the electron transfer rate constant (0.148(+/-0.005) s(-1) of FeII(CN)6(4-) at 25 degrees C is very similar to that of W(IV)(CN)8(4-) (0.072(+/-0.011) s(-1)). The entropy values of the adduct formations and the activation energies of the electron transfer rates were determined by the temperature dependence of the dissociation constants of the adducts and the electron transfer rates. The enthalpy values of the formation of adducts are almost zero, so that the driving forces to form the adducts are mainly derived from the entropy. The activation energy of the electron transfer rate of FeII(CN)6(4-) is very similar to that of W(IV)(CN)8(4-). The formation of the adduct between FeII(CN)6(4-) and the enzyme was inhibited by the presence of various anions (ClO4-, SO4(2-), SCN-, and N3-). The bulky anions SO4(2-) and ClO4- behave as competitive inhibitors for FeII(CN)6(4-); these anions should interact mainly with Arg143, as it has a positive charge at the entrance of the active cavity. The competitive inhibition constants of ClO4-, SO4(2-), and SCN- were 0.010, 0.012, and 0.008 M. The azide ion, which is smaller than SO4(2-) or ClO4-, shows mixed inhibition, because N3- can interact with Arg143 (competitive inhibition) and also directly binds to the cupric ion in h-SOD (noncompetitive inhibition). The competitive and noncompetitive inhibition constants of N3- were 0.004 and 0.016 M, respectively.

journal_name

Arch Biochem Biophys

journal_title

Archives of biochemistry and biophysics

authors

Hirose J,Minakami M,Settu K,Tsukahara K,Ueda J,Ozawa T

doi

10.1006/abbi.2000.2055

subject

Has Abstract

pub_date

2000-11-15 00:00:00

pages

246-55

issue

eissn

0003-9861

issn

1096-0384

pii

S0003986100920551

journal_volume

383

pub_type

杂志文章

在线工具

Reaction mechanism of electron transfer from FeII(CN)6(4-) or W(IV)(CN)8(4-) to the cupric ions in human copper, zinc superoxide dismutase.