title: Ceruloplasmin is an endogenous inhibitor of myeloperoxidase.
abstract: Myeloperoxidase is a neutrophil enzyme that promotes oxidative stress in numerous inflammatory pathologies. It uses hydrogen peroxide to catalyze the production of strong oxidants including chlorine bleach and free radicals. A physiological defense against the inappropriate action of this enzyme has yet to be identified. We found that myeloperoxidase oxidized 75% of the ascorbate in plasma from ceruloplasmin knock-out mice, but there was no significant loss in plasma from wild type animals. When myeloperoxidase was added to human plasma it became bound to other proteins and was reversibly inhibited. Ceruloplasmin was the predominant protein associated with myeloperoxidase. When the purified proteins were mixed, they became strongly but reversibly associated. Ceruloplasmin was a potent inhibitor of purified myeloperoxidase, inhibiting production of hypochlorous acid by 50% at 25 nm. Ceruloplasmin rapidly reduced Compound I, the Fe(V) redox intermediate of myeloperoxidase, to Compound II, which has Fe(IV) in its heme prosthetic groups. It also prevented the fast reduction of Compound II by tyrosine. In the presence of chloride and hydrogen peroxide, ceruloplasmin converted myeloperoxidase to Compound II and slowed its conversion back to the ferric enzyme. Collectively, our results indicate that ceruloplasmin inhibits myeloperoxidase by reducing Compound I and then trapping the enzyme as inactive Compound II. We propose that ceruloplasmin should provide a protective shield against inadvertent oxidant production by myeloperoxidase during inflammation.
authors.affiliation: Centre for Free Radical Research, Department of Pathology, University of Otago, Christchurch, Christchurch 8140, New Zealand.
authors.forename: Anna L P
authors.initials: AL
authors.lastname: Chapman
authors.forename: Tessa J
authors.initials: TJ
authors.lastname: Mocatta
authors.forename: Sruti
authors.initials: S
authors.lastname: Shiva
authors.forename: Antonia
authors.initials: A
authors.lastname: Seidel
authors.forename: Brian
authors.initials: B
authors.lastname: Chen
authors.forename: Irada
authors.initials: I
authors.lastname: Khalilova
authors.forename: Martina E
authors.initials: ME
authors.lastname: Paumann-Page
authors.forename: Guy N L
authors.initials: GN
authors.lastname: Jameson
authors.forename: Christine C
authors.initials: CC
authors.lastname: Winterbourn
authors.forename: Anthony J
authors.initials: AJ
authors.lastname: Kettle
mesh_terms: D000818:Animals; D001205:Ascorbic Acid / Q000097:blood; D002570:Ceruloplasmin / Q000737:chemistry* / Q000235:genetics / Q000302:isolation & purification / Q000378:metabolism; D004791:Enzyme Inhibitors / Q000097:blood / Q000737:chemistry* / Q000302:isolation & purification; D006801:Humans; D006997:Hypochlorous Acid / Q000097:blood; D007249:Inflammation / Q000097:blood; D051379:Mice; D018345:Mice, Knockout; D010084:Oxidation-Reduction; D009195:Peroxidase / Q000037:antagonists & inhibitors* / Q000097:blood / Q000737:chemistry* / Q000235:genetics / Q000302:isolation & purification; D011485:Protein Binding
chemical_list: D004791:Enzyme Inhibitors; D006997:Hypochlorous Acid; D009195:Peroxidase; D002570:Ceruloplasmin; D001205:Ascorbic Acid