Myeloperoxidase acts as a source of free iron during steady-state catalysis by a feedback inhibitory pathway

Dhiman Maitra, Faten Shaeib, Ibrahim Abdulhamid, Rasha M. Abdulridha, Ghassan M. Saed, Michael Peter Diamond, Subramaniam Pennathur, Husam M. Abu-Soud

Research output: Contribution to journalArticle

26 Citations (Scopus)

Abstract

Myeloperoxidase (MPO) is a heme-containing enzyme that generates hypochlorous acid (HOCl) from chloride (Cl-) and hydrogen peroxide (H 2O2). It is implicated in the pathology of several chronic inflammatory conditions such as cardiovascular and pulmonary diseases and cancer. Recently we have shown that HOCl can destroy the heme prosthetic group of hemoproteins. Here, we investigated whether the HOCl formed during steady-state catalysis is able to destroy the MPO heme moiety and thereby function as a major source of free iron. UV-visible spectra and H 2O2-specific electrode measurements recorded during steady-state HOCl synthesis by MPO showed that the degree of MPO heme destruction increased after multiple additions of H2O2 (10 mM), precluding the enzyme from functioning at maximum activity (80-90% inhibition). MPO heme destruction occurred only in the presence of Cl-. Stopped-flow measurements revealed that the HOCl-mediated MPO heme destruction was complex and occurred through transient ferric species whose formation and decay kinetics indicated it participates in heme destruction along with subsequent free iron release. MPO heme depletion was confirmed by the buildup of free iron utilizing the ferrozine assay. Hypochlorous acid, once generated, first equilibrates in the solution as a whole before binding to the heme iron and initiating heme destruction. Eliminating HOCl from the MPO milieu by scavenging HOCl, destabilizing the MPO-Compound I-Cl complex that could be formed during catalysis, and/or inhibiting MPO catalytic activity partially or completely protects MPO from HOCl insults. Collectively, this study elucidates the bidirectional relationship between MPO and HOCl, which highlights the potential role of MPO as a source of free iron.

Original languageEnglish (US)
Pages (from-to)90-98
Number of pages9
JournalFree Radical Biology and Medicine
Volume63
DOIs
StatePublished - Jan 1 2013

Fingerprint

Hypochlorous Acid
Catalysis
Peroxidase
Iron
Heme
Feedback
Ferrozine
Pulmonary diseases
Scavenging
Pathology
Flow measurement
Enzymes
Prosthetics
Hydrogen Peroxide
Lung Diseases
Chlorides
Assays
Catalyst activity
Lung Neoplasms
Electrodes

Keywords

  • Feedback inhibition
  • Free iron
  • Free radicals
  • Hypochlorous acid
  • Inflammation
  • Myeloperoxidase
  • Oxidative stress

ASJC Scopus subject areas

  • Biochemistry
  • Physiology (medical)

Cite this

Myeloperoxidase acts as a source of free iron during steady-state catalysis by a feedback inhibitory pathway. / Maitra, Dhiman; Shaeib, Faten; Abdulhamid, Ibrahim; Abdulridha, Rasha M.; Saed, Ghassan M.; Diamond, Michael Peter; Pennathur, Subramaniam; Abu-Soud, Husam M.

In: Free Radical Biology and Medicine, Vol. 63, 01.01.2013, p. 90-98.

Research output: Contribution to journalArticle

Maitra, Dhiman ; Shaeib, Faten ; Abdulhamid, Ibrahim ; Abdulridha, Rasha M. ; Saed, Ghassan M. ; Diamond, Michael Peter ; Pennathur, Subramaniam ; Abu-Soud, Husam M. / Myeloperoxidase acts as a source of free iron during steady-state catalysis by a feedback inhibitory pathway. In: Free Radical Biology and Medicine. 2013 ; Vol. 63. pp. 90-98.
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abstract = "Myeloperoxidase (MPO) is a heme-containing enzyme that generates hypochlorous acid (HOCl) from chloride (Cl-) and hydrogen peroxide (H 2O2). It is implicated in the pathology of several chronic inflammatory conditions such as cardiovascular and pulmonary diseases and cancer. Recently we have shown that HOCl can destroy the heme prosthetic group of hemoproteins. Here, we investigated whether the HOCl formed during steady-state catalysis is able to destroy the MPO heme moiety and thereby function as a major source of free iron. UV-visible spectra and H 2O2-specific electrode measurements recorded during steady-state HOCl synthesis by MPO showed that the degree of MPO heme destruction increased after multiple additions of H2O2 (10 mM), precluding the enzyme from functioning at maximum activity (80-90{\%} inhibition). MPO heme destruction occurred only in the presence of Cl-. Stopped-flow measurements revealed that the HOCl-mediated MPO heme destruction was complex and occurred through transient ferric species whose formation and decay kinetics indicated it participates in heme destruction along with subsequent free iron release. MPO heme depletion was confirmed by the buildup of free iron utilizing the ferrozine assay. Hypochlorous acid, once generated, first equilibrates in the solution as a whole before binding to the heme iron and initiating heme destruction. Eliminating HOCl from the MPO milieu by scavenging HOCl, destabilizing the MPO-Compound I-Cl complex that could be formed during catalysis, and/or inhibiting MPO catalytic activity partially or completely protects MPO from HOCl insults. Collectively, this study elucidates the bidirectional relationship between MPO and HOCl, which highlights the potential role of MPO as a source of free iron.",
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T1 - Myeloperoxidase acts as a source of free iron during steady-state catalysis by a feedback inhibitory pathway

AU - Maitra, Dhiman

AU - Shaeib, Faten

AU - Abdulhamid, Ibrahim

AU - Abdulridha, Rasha M.

AU - Saed, Ghassan M.

AU - Diamond, Michael Peter

AU - Pennathur, Subramaniam

AU - Abu-Soud, Husam M.

PY - 2013/1/1

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N2 - Myeloperoxidase (MPO) is a heme-containing enzyme that generates hypochlorous acid (HOCl) from chloride (Cl-) and hydrogen peroxide (H 2O2). It is implicated in the pathology of several chronic inflammatory conditions such as cardiovascular and pulmonary diseases and cancer. Recently we have shown that HOCl can destroy the heme prosthetic group of hemoproteins. Here, we investigated whether the HOCl formed during steady-state catalysis is able to destroy the MPO heme moiety and thereby function as a major source of free iron. UV-visible spectra and H 2O2-specific electrode measurements recorded during steady-state HOCl synthesis by MPO showed that the degree of MPO heme destruction increased after multiple additions of H2O2 (10 mM), precluding the enzyme from functioning at maximum activity (80-90% inhibition). MPO heme destruction occurred only in the presence of Cl-. Stopped-flow measurements revealed that the HOCl-mediated MPO heme destruction was complex and occurred through transient ferric species whose formation and decay kinetics indicated it participates in heme destruction along with subsequent free iron release. MPO heme depletion was confirmed by the buildup of free iron utilizing the ferrozine assay. Hypochlorous acid, once generated, first equilibrates in the solution as a whole before binding to the heme iron and initiating heme destruction. Eliminating HOCl from the MPO milieu by scavenging HOCl, destabilizing the MPO-Compound I-Cl complex that could be formed during catalysis, and/or inhibiting MPO catalytic activity partially or completely protects MPO from HOCl insults. Collectively, this study elucidates the bidirectional relationship between MPO and HOCl, which highlights the potential role of MPO as a source of free iron.

AB - Myeloperoxidase (MPO) is a heme-containing enzyme that generates hypochlorous acid (HOCl) from chloride (Cl-) and hydrogen peroxide (H 2O2). It is implicated in the pathology of several chronic inflammatory conditions such as cardiovascular and pulmonary diseases and cancer. Recently we have shown that HOCl can destroy the heme prosthetic group of hemoproteins. Here, we investigated whether the HOCl formed during steady-state catalysis is able to destroy the MPO heme moiety and thereby function as a major source of free iron. UV-visible spectra and H 2O2-specific electrode measurements recorded during steady-state HOCl synthesis by MPO showed that the degree of MPO heme destruction increased after multiple additions of H2O2 (10 mM), precluding the enzyme from functioning at maximum activity (80-90% inhibition). MPO heme destruction occurred only in the presence of Cl-. Stopped-flow measurements revealed that the HOCl-mediated MPO heme destruction was complex and occurred through transient ferric species whose formation and decay kinetics indicated it participates in heme destruction along with subsequent free iron release. MPO heme depletion was confirmed by the buildup of free iron utilizing the ferrozine assay. Hypochlorous acid, once generated, first equilibrates in the solution as a whole before binding to the heme iron and initiating heme destruction. Eliminating HOCl from the MPO milieu by scavenging HOCl, destabilizing the MPO-Compound I-Cl complex that could be formed during catalysis, and/or inhibiting MPO catalytic activity partially or completely protects MPO from HOCl insults. Collectively, this study elucidates the bidirectional relationship between MPO and HOCl, which highlights the potential role of MPO as a source of free iron.

KW - Feedback inhibition

KW - Free iron

KW - Free radicals

KW - Hypochlorous acid

KW - Inflammation

KW - Myeloperoxidase

KW - Oxidative stress

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