Record Details

Mechanism of Horseradish Peroxidase Catalyzed Epinephrine Oxidation: Obligatory Role of Endogenous O2 - and H2O2

EPrints@IICB

View Archive Info
 
 
Field Value
 
Title Mechanism of Horseradish Peroxidase Catalyzed Epinephrine Oxidation: Obligatory Role of Endogenous O2 - and H2O2
 
Creator Adak, Subrata
Bandyopadhyay, Uday
Bandyopadhyay, Debashis
Banerjee, Ranajit K
 
Subject Structural Biology & Bioinformatics
 
Description Horseradish peroxidase (HRP) catalyzes cyanide sensitive oxidation of epinephrine to
adrenochrome at physiological pH in the absence of added H2O2 with concurrent consumption of O2.
Both adrenochrome formation and O2 consumption are significantly inhibited by catalase, indicating a
peroxidative mechanism as a major part of oxidation due to intermediate formation of H2O2. Sensitivity
to superoxide dismutase (SOD) also indicates involvement of O2
- in the oxidation. Although SOD-mediated
H2O2 formation should continue epinephrine oxidation through a peroxidative mechanism, low catalytic
turnover, on the contrary, indicates that O2
- takes part in a vital reaction to form an intermediate for
adrenochrome formation and O2 consumption. Generation of O2
- is evidenced by ferricytochrome c
reduction sensitive to SOD. On addition of H2O2, both adrenochrome formation and O2 consumption are
further increased due to reaction of molecular oxygen with some intermediate oxidation product.
Peroxidative oxidation proceeds by one-electron transfer generating o-semiquinone and similar free radicals
which when stabilized with Zn2+ or spin-trap, R-phenyl-tert-butylnitrone (PBN), inhibit adrenochrome
formation and O2 consumption. The free radicals thus favor reduction of O2 rather than the disproportionation
reaction. Spectral studies indicate that, during epinephrine oxidation in the presence of catalase,
HRP remains in the ferric state absorbing at 403 nm. This suggests that HRP catalyzes epinephrine oxidation
by its oxidase activity through Fe3+/Fe2+ shuttle consuming O2, where the rate of reduction of ferric HRP
with epinephrine is slower than subsequent oxidation of ferrous HRP by O2 to form compound III.
Compound III was not detected spectrally because of its quick reduction to the ferric state by epinephrine
or its subsequent oxidation product. In the absence of catalase, peroxidative cycles predominate when
HRP still remains in the ferric state through the transient formation of compounds I and II not detectable
spectrally. Among various mono- and dihydroxyl aromatic donors tested, only epinephrine shows the
oxidase reaction. Binding studies indicate that epinephrine interferes with the binding of CN-, SCN-,
and guaiacol indicating that HRP preferentially binds epinephrine near the heme iron close to the anion
or aromatic donor binding site to catalyze electron transfer for oxidation. HRP thus initiates epinephrine
oxidation by its oxidase activity generating O2
- and H2O2. Once H2O2 is generated, the peroxidative
cycle continues with the consumption of O2, through the intermediate formation of O2 - and H2O2 which play an obligatory role in subsequent cycles of peroxidation.
 
Date 1998
 
Type Article
PeerReviewed
 
Format application/pdf
 
Identifier http://www.eprints.iicb.res.in/856/1/BIOCHEMISTRY%2C_37(_48)%2C__16922%2D16933[4].pdf
Adak, Subrata and Bandyopadhyay, Uday and Bandyopadhyay, Debashis and Banerjee, Ranajit K (1998) Mechanism of Horseradish Peroxidase Catalyzed Epinephrine Oxidation: Obligatory Role of Endogenous O2 - and H2O2. Biochemistry, 37 (48). pp. 16922-16933.
 
Relation http://dx.doi.org/10.1021/bi980899l
http://www.eprints.iicb.res.in/856/