Haem Propionates Control Oxidative and Reductive Activities of Horseradish Peroxidase by Maintaining the Correct Orientation of the Haem
IR@IICB: CSIR-Indian Institute of Chemical Biology, Kolkata
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| Title |
Haem Propionates Control Oxidative and Reductive Activities of Horseradish Peroxidase by Maintaining the Correct Orientation of the Haem
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| Creator |
Adak, Subrata
Banerjee, Ranajit K |
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| Subject |
Structural Biology & Bioinformatics
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| Description |
The role of haem propionates in oxidative and reductive reactions
catalysed by horseradish peroxidase (HRP) was studied after
successful reconstitution of ferric protoporphyrin IX dimethyl
ester (PPDME) into the apoperoxidase. The reconstituted enzyme
oxidizes neither guaiacol (aromatic electron donor) nor
iodide or thiocyanate (inorganic donor). Although the reconstituted
enzyme binds guaiacol with a similar Kd (13 mM) to that
of the native enzyme (10 mM), the Kd for SCN− binding (5 mM)
is decreased 20-fold compared with that of the native enzyme
(100 mM). This indicates that haem propionates hinder the entry
or binding of inorganic anion to the active site of the native
HRP. However, the reconstituted enzyme is catalytically inactive
as it does not form spectroscopically detectable compound II
with H#O#. CD measurements indicate a signiÆcant loss of haem
CD spectrum of the reconstituted enzyme at 409 nm, suggesting
a loss of asymmetry of the haem±protein interaction. Thus the
inability of the reconstituted enzyme to form catalytic intermediates
results from the change in orientation of the haem due
to loss of interactions via the haem propionates. HRP also
catalyses reductive reactions such as reduction of iodine (I+) in
the presence of EDTA and H#O#. The reconstituted enzyme
cannot catalyse I+ reduction because of the loss of I+ binding to
the haem propionate. Since I+ reduction requires formation of
the catalytically active enzyme±I+±EDTA ternary complex, the
loss of reductive activity is primarily due to the loss of active
enzyme formation. Haem propionates thus play a vital role in the
oxidative and reductive reactions of HRP by favouring the
formation of catalytic intermediates with H#O# by maintaining
the correct orientation of the haem with respect to the surrounding
residues.
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| Date |
1998
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| Type |
Article
PeerReviewed |
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| Format |
application/pdf
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| Identifier |
http://www.eprints.iicb.res.in/1034/1/Biojheme.pdf
Adak, Subrata and Banerjee, Ranajit K (1998) Haem Propionates Control Oxidative and Reductive Activities of Horseradish Peroxidase by Maintaining the Correct Orientation of the Haem. Biochemical Journal, 334. pp. 51-56. |
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| Relation |
http://dx.doi.org/
http://www.eprints.iicb.res.in/1034/ |
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