title: Mechanism of low-density lipoprotein oxidation by hemoglobin-derived iron.
abstract: Excellular hemoglobin is an extremely active oxidant of low-density lipoproteins (LDL), a phenomenon explained so far by different mechanisms. In this study, we analyzed the mechanism of met-hemoglobin oxidability by comparing its mode of operation with other hemoproteins, met-myoglobin and horseradish peroxidase (HRP) or with free hemin. The kinetics of met-hemoglobin activity toward LDL lipids and protein differed from that of met-myoglobin and HRP, both quantitatively and qualitatively. Those differences were further clarified by analyzing heme transfer from the above-mentioned hemoproteins to LDL. It appeared that met-hemoglobin transferred most of its hemin to LDL, and the presence of H(2)O(2) accelerated the process. In contrast, met-myoglobin partially released hemin, but only in the presence of H(2)O(2), while HRP could not transfer heme at all. The minor amount of hemin transferred from met-myoglobin to LDL sufficed to trigger ApoB oxidation, forming covalent aggregates via inter-bityrosines. This indicated that heme bound to high affinity site(s) is responsible for oxidation. LDL components providing the sites were analyzed by binding heme-CO monomers to LDL. Soret spectra revealed that the high affinity site of monomeric hemin is located on the LDL protein, ApoB. The complex heme-CO-ApoB underwent instantaneous oxidation to hemin-ApoB, and the bound hemin then slowly disintegrated in conjunction with LDL oxidation. Hemopexin prevented LDL oxidation by trapping hemoprotein transferable heme. We concluded that met-hemoglobin exerts its oxidative activity on LDL via transfer of heme, which serves as a vehicle for iron insertion into the LDL protein, leading to formation of atherogenic LDL aggregates.
authors.affiliation: Sackler Institute of Molecular Medicine, Department of Human Genetics and Molecular Medicine, Sackler Faculty of Medicine, Tel Aviv University, 69978 Tel-Aviv, Israel.
authors.forename: Natalie
authors.initials: N
authors.lastname: Grinshtein
authors.forename: Vladimir Varlen
authors.initials: VV
authors.lastname: Bamm
authors.forename: Vladimir Abraham
authors.initials: VA
authors.lastname: Tsemakhovich
authors.forename: Nurith
authors.initials: N
authors.lastname: Shaklai
mesh_terms: D000818:Animals; D001055:Apolipoproteins B / Q000378:metabolism; D002248:Carbon Monoxide / Q000737:chemistry; D002417:Cattle; D003619:Dansyl Compounds / Q000737:chemistry; D006418:Heme / Q000378:metabolism; D006466:Hemopexin / Q000378:metabolism / Q000494:pharmacology; D006735:Horseradish Peroxidase / Q000378:metabolism; D006736:Horses; D006801:Humans; D006861:Hydrogen Peroxide / Q000494:pharmacology; D007501:Iron / Q000378:metabolism*; D007700:Kinetics; D008077:Lipoproteins, LDL / Q000378:metabolism*; D008706:Methemoglobin / Q000378:metabolism*; D008786:Metmyoglobin / Q000378:metabolism; D010084:Oxidation-Reduction; D013050:Spectrometry, Fluorescence / Q000379:methods; D017392:Thiobarbituric Acid Reactive Substances / Q000378:metabolism
chemical_list: D001055:Apolipoproteins B; D003619:Dansyl Compounds; D008077:Lipoproteins, LDL; D017392:Thiobarbituric Acid Reactive Substances; D008786:Metmyoglobin; D006418:Heme; D002248:Carbon Monoxide; D008706:Methemoglobin; D006466:Hemopexin; D006861:Hydrogen Peroxide; D007501:Iron; D006735:Horseradish Peroxidase