アラシキ　ノブト   Arashiki Nobuto   新敷　信人    所属   医学部 医学科    職種   助教
論文種別	原著
言語種別	英語
査読の有無	査読あり
表題	Membrane Peroxidation and Methemoglobin Formation are Both Necessary for Band 3 Clustering: Mechanistic Insights into Human Erythrocyte Senescence
掲載誌名	正式名：Biochemistry 略　 称：Biochemistry ISSNコード：00062960
巻・号・頁	52,pp.5760-5769
著者・共著者	Arashiki Nobuto†, Kimata Naoki, Manno Sumie, Mohandas Narla, Takakuwa Yuichi*
担当区分	筆頭著者
発行年月	2013/07
概要	Oxidative damage and clustering of band 3 in the membrane have been implicated in the removal of senescent human erythrocytes from the circulation at the end of their 120 day life span. However, the biochemical and mechanistic events leading to band 3 cluster formation have yet to be fully defined. Here we show that while neither membrane peroxidation nor methemoglobin (MetHb) formation on their own can induce band 3 clustering in the human erythrocytes, they can do so when acting in combination. We further show that binding of MetHb to the cytoplasmic domain of band 3 in peroxidized, but not in untreated, erythrocyte membranes induces cluster formation. Age-fractionated populations of erythrocytes from normal human blood, obtained by a density gradient procedure, have allowed us to examine a subpopulation, highly enriched in senescent cells. We have found that band 3 clustering is a feature of only this small fraction, amounting to ∼0.1% of total circulating erythrocytes. These senescent cells are characterized by an increased proportion of MetHb as a result of reduced nicotinamide adenine dinucleotide dependent reductase activity and accumulated oxidative membrane damage. These findings have allowed us to establish that the combined effects of membrane peroxidation and MetHb formation are necessary for band 3 clustering, and this is a very late event in erythrocyte life. A plausible mechanism for the combined effects of membrane peroxidation and MetHb is proposed, involving high-affinity cooperative binding of MetHb to the cytoplasmic domain of oxidized band 3, probably because of its carbonylation, rather than other forms of oxidative damage. This modification leads to dissociation of ankyrin from band 3, allowing the tetrameric MetHb to cross-link the resulting freely diffusible band 3 dimers, with formation of clusters.