1,721,121 research outputs found
Modified Microperoxidases Exhibit Different Reactivity Towards Phenolic Substrates
No full textThe reactivity of several microperoxidase derivatives with different
distal-site environments has been studied. The distal-site environments
of these heme peptides include a positively charged
one, an uncharged environment, two bulky and doubly or triply
positively charged ones, and one containing aromatic apolar residues.
The reactivity in the catalytic oxidation of two representative
phenols, carrying opposite charges, by hydrogen peroxide
has been investigated. This allows the determination of the binding
constants and of the electron-transfer rate from the phenol
to the catalyst in the substrate/microperoxidase complex. The
electron-transfer rates scarcely depend on the redox and charge
properties of the phenol, but depend strongly on the microperoxidase.
Information on the disposition of the substrate in the adducts
with the microperoxidases has been obtained through determination
of the paramagnetic contribution to the 1H NMR relaxation
rates of the protons of the bound substrates. The data
show that the electron-transfer rate drops when the substrate
binds too far away from the iron and that the phenols bind to
microperoxidases at similar distances to those observed with peroxidases.
While the reaction rate of microperoxidases with peroxide
is significantly smaller than that of the enzymes, the efficiency
in the one-electron oxidation of phenolic substrates is almost
comparable. Interestingly, the oxyferryl form of the triply positively
charged microperoxidases shows a reactivity larger than that
exhibited by horseradish peroxidas
Validation of paramagnetic cross correlation rates for solution structure determination of high spin iron(III) heme proteins
No full textReactivity study on microperoxidase-8
Full text linkThe catalytic activity of the microperoxidase-8/
H2O2 system toward tyramine and 3-(4-hydroxyphenyl)
propionic acid has been determined in acetate buffer,
pH 5.0. Operating with a strong excess of hydrogen
peroxide, the rate-determining step of the reaction was
substrate oxidation. Owing to the fast microperoxidase-
8 degradation, only the very initial phase of the reactions
were analyzed. The reaction rates follow a substrate
saturation behavior, with turnover numbers [kcat=
26±1 s)1 for 3-(4-hydroxyphenyl)propionic acid and
kcat=22±1 s)1 for tyramine] that were similar for the
two substrates. In contrast, the KM values indicated a
reduced affinity for the catalyst active species by the
positively charged phenol, probably due to repulsive
interaction with the protonated N-terminal microperoxidase-
8 amino group. The reactivity of the catalyst
active species was studied upon incubation of microperoxidase-
8 with a small excess hydrogen peroxide, followed
by reaction with the phenolic substrates. The
kinetic analysis showed that more than two active species
are accumulated. The species responsible for the
faster reactions was present in solution as a minor
fraction. The active intermediate which accumulated in a
larger amount (intermediate III) has a reduced substrate
oxidation activity. Comparison of this activity with the
kinetic constants obtained under turnover experiments
shows that intermediate III is not involved in the microperoxidase-
8 catalytic cycle. The active species of the
catalytic process are intermediates I and II, which in the
absence of substrate rapidly convert to intermediate III
Mechanistic Insight into the Catechol Oxidase Activity by a Biomimetic Dinuclear Copper Complex
Full text linkThe biomimetic catalytic oxidation of 3,5-ditert-
butylcatechol by the dicopper(II) complex of the
ligand a,a¢-bis{bis[1-(1¢-methyl-2¢-benzimidazolyl)
methyl]amino}-m-xylene in the presence of dioxygen has
been investigated as a function of temperature and pH in
a mixed aqueous/organic solvent. The catalytic cycle
occurs in two steps, the first step being faster than the
second step. In the first step, one molecule of catechol is
oxidized by the dicopper(II) complex, and the copper(II)
centers are reduced. From the pH dependence, it is deduced
that the active species of the process is the
monohydroxo form of the dinuclear complex. In the
second step, the second molecule of catechol is oxidized
by the dicopper(I)-dioxygen complex formed upon
oxygenation of the reduced complex. In both cases,
catechol oxidation is an inner-sphere electron transfer
process involving binding of the catechol to the active
species. The binary catechol-dicopper(II) complex
formed in the first step could be characterized at very
low temperature (90 C), where substrate oxidation is
blocked. On the contrary, the ternary complex of dicopper(
I)-O2-catechol relevant to the second step does
not accumulate in solution and could not be characterized,
even at low temperature. The investigation of the
biphasic kinetics of the catalytic reaction over a range of
temperatures allowed the thermodynamic (DH and DS)
and activation parameters (DH „ and DS „ ) connected
with the key steps of the catecholase process to be
obtained
Potential applications of peroxidases in the fine chemical industries
No full textA description of selected types of reactions catalyzed by heme peroxidases is given. In particular, the discussion is focused mainly on those of potential interest for fine chemical synthesis. The division into subsections has been done from the point of view of the enzyme action, i.e., giving emphasis to themechanism of the enzymatic reaction, and from that of the substrate, i.e., analyzing the type of transformation promoted by the enzyme. These two approaches have several points in common
X-Ray absorption spectroscopy quantitative analysis of biomimetic copper(II) complexes with tridentate nitrogen ligands mimicking the tris(imidazole) array of protein centres.
No full textCoordination and redox properties of copper interaction with α-synuclein
Full text linkParkinson's disease (PD) is a severe neurodegenerative disorder affecting movements. After Alzheimer's disease, it is the most common form of neurodegeneration. PD is characterized by the loss of neurons producing dopamine and by the presence of protein aggregates in the brain, known as Lewy bodies. The main constituent of Lewy bodies is the misfolded form of α-synuclein (αSyn), able to form oligomers and fibrils. In addition to protein aggregation, brain damage induced by oxidative stress, is also a frequent phenomenon in PD. αSyn is able to bind Copper ions in both Cu(II) and Cu(I) oxidation states. The metal binding is also maintained when αSyn interacts with membranes. Interestingly, copper binding to αSyn has strong impact either in protein misfolding or in free radical formation, such to provide a link between protein aggregation and oxidative damage. In this review the role of copper and αSyn in PD is discussed with a particular emphasis to elucidate (i) the interaction between copper and αSyn; (ii) the reactivity and (iii) potential toxicity associated with copper-αSyn complexes
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