Pore Formation and Uncoupling Initiate a Ca2+-Independent Degradation of Mitochondrial Phospholipids

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• 作者：Kimberly M. Broekemeier ; James R. Iben ; Emily G. LeVan ; Elliott D. Crouser ; and Douglas R. Pfeiffer
• 刊名：Biochemistry
• 出版年：2002
• 出版时间：June 18, 2002
• 年：2002
• 卷：41
• 期：24
• 页码：7771 - 7780
• 全文大小：141K
• 年卷期：v.41,no.24(June 18, 2002)
• ISSN：1520-4995

文摘

Mitochondria contain a type IIA secretory phospholipase A₂ that has been thought to hydrolyzephospholipids following Ca²⁺ accumulation and induction of the permeability transition. These enzymesnormally require millimolar Ca²⁺ for optimal activity; however, no dependence of the mitochondrial activityon Ca²⁺ can be demonstrated upon equilibrating the matrix space with extramitochondrial Ca²⁺ buffers.Ca²⁺-independent activity is seen following protonophore-mediated uncoupling, when uncoupling arisesthrough alamethicin-mediated pore formation, or upon opening the permeability transition pore. Underthe latter conditions, activity continues in the presence of excess EGTA but is somewhat enhanced byexogenous Ca²⁺. The Ca²⁺-independent activity is best seen in media of high ionic strength and displaysa broad pH optimum located between pH 8 and pH 8.5. It is strongly inhibited by bromoenol lactone butnot by arachidonyl trifluoromethyl ketone, dithiothreitol, and other inhibitors of particular phospholipaseA₂ classes. Immunoanalysis of mitochondria and mitochondrial subfractions shows that a membrane-bound protein is present that is recognized by antibody against an authentic iPLA₂ that was first found inP388D₁ cells. It is concluded that mitochondria contain a distinct Ca²⁺-independent phospholipase A₂that is regulated by bioenergetic parameters. It is proposed that this enzyme, rather than the Ca²⁺-dependenttype IIA phospholipase A₂, initiates the removal of poorly functioning mitochondria by processes involvingautolysis.