Communications
[
24]
observations with a chemical model and the mechanism
proposed above.
[12] Rates were determined on a Varian CARY50 spectrophoto-
meter equipped with a temperature controller. The rate law for
II
pre-equilibrium kinetics [Eq. (1)], as followed by Cu Ab, is
In conclusion, we have established the catalytic activities
of CuAb1–20 toward the relatively inactive species (according
to their k values) catechol and phenol in the presence and
shown in Equation (2), in which kcat and K’app are the first-order
rate constant and apparent dissociation constant, respectively, S
is the substrate, P is the product, and vbg is the autooxidation rate.
0
absence of H O in aqueous solutions at near-physiological
2
2
k1
k
cat
II
II
II
conditions. The reaction patterns are consistent with the
mechanisms carried out by Type-3 copper centers as observed
with catechol oxidase and tyrosinase and their dinuclear
Cu Ab + S!AbCu –S!Cu Ab + P
(1
kꢀ1
kcat½CuAb½S
v = v
+
0
(2)
bg
K
app
þ½S
[
8,22]
model systems.
So far these results are unique in metal-
[
13] A. Rompel, H. Fischer, D. Meiwes, K. Bꢁldt-Karentzopoulos, R.
centered redox chemistry related to Alzheimerꢀs disease and
are expected to offer further insight into the neuropathology
of this disease, as it is suspected to be linked with, besides
many other factors, the oxidation of mono- and diphenol-
containing neurotransmitters such as dopamine, epinephrine,
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1
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lead to different treatment strategies toward this disease.
[
1
[
[17] The Hill equation can serve as a general model for cooperativity
as reflected by the Hill coefficient q, which deviates from unity in
Received: March 19, 2005
the presence of cooperativity [Eq. (3); K
x
is the intrinsic
Published online: July 29, 2005
dissociation constant].
q
v0
½CuAb
=
q
(3)
Keywords: b-amyloids · Alzheimer’s disease · copper ·
oxidoreductases · peptides · redox chemistry
vmax Kxþ½CuAb
.
[
18] In case of two-substrate catalysis, such as phenol hydroxylation/
oxidation and catechol oxidation in the presence of H O , both
2
2
substrates can interact with the metal center independently. The
data are fitted to the Hanes plot [Eq. (4)] to yield true values of
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[
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substrate dissociation constants K’.
1, 231– 239.
ꢀ
ꢁ
0
½
S ð1þK0a=½H2O2Þ
K
Ki
½H2O2
[
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=
[S] +
1+
(4)
v0
vmax
vmax
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002, p. 119.
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2
[
10] Phenol hydroxylation/oxidation and catechol oxidation were
[
11]
performed as previously reported with minor changes to suit
the current studies. The same molar concentrations of phenol or
catechol and 3-methyl-2-benzothiazolinone hydrazone (MBTH,
an indicator of o-quinone) were mixed in HEPES buffer
1
(
(
100 mm) at pH 7.00 in the presence of CuAb1–20 at 5.0 mm
phenol hydroxylation/oxidation) or 0.50 mm (catechol oxida-
tion). The red adduct of the o-quinone product was monitored at
ꢀ1
ꢀ1
5
00 nm (e = 32,500m cm ; see Figure 1c). The autooxidation
of phenol and catechol were determined under the same
conditions in the absence of CuAb1–20. The 1–20 fragment of
Ab was synthesized at the Peptide Center of the University of
South Florida. The identity of the peptide was confirmed with a
Bruker MALDI-TOF mass spectrometer.
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5
504
ꢀ 2005 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Angew. Chem. Int. Ed. 2005, 44, 5501 –5504