Peroxidase Activity and Structural Transitions of Cytochrome c Bound to Cardiolipin-Containing Membranes

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• 作者：Natalia A. Belikova ; Yury A. Vladimirov ; Anatoly N. Osipov ; Alexandr A. Kapralov ; Vladimir A. Tyurin ; Maksim V. Potapovich ; Liana V. Basova ; Jim Peterson ; Igor V. Kurnikov ; and Valerian E. Kagan
• 刊名：Biochemistry
• 出版年：2006
• 出版时间：April 18, 2006
• 年：2006
• 卷：45
• 期：15
• 页码：4998 - 5009
• 全文大小：240K
• 年卷期：v.45,no.15(April 18, 2006)
• ISSN：1520-4995

文摘

During apoptosis, cytochrome c (cyt c) is released from intermembrane space of mitochondriainto the cytosol where it triggers the caspase-dependent machinery. We discovered that cyt c plays anothercritical role in early apoptosis as a cardiolipin (CL)-specific oxygenase to produce CL hydroperoxidesrequired for release of pro-apoptotic factors [Kagan, V. E., et al. (2005) Nat. Chem. Biol. 1, 223-232].We quantitatively characterized the activation of peroxidase activity of cyt c by CL and hydrogen peroxide.At low ionic strength and high CL/cyt c ratios, peroxidase activity of the CL/cyt c complex was increased>50 times. This catalytic activity correlated with partial unfolding of cyt c monitored by Trp₅₉ fluorescenceand absorbance at 695 nm (Fe-S(Met₈₀) band). The peroxidase activity increase preceded the loss ofprotein tertiary structure. Monounsaturated tetraoleoyl-CL (TOCL) induced peroxidase activity andunfolding of cyt c more effectively than saturated tetramyristoyl-CL (TMCL). TOCL/cyt c complex wasfound more resistant to dissociation by high salt concentration. These findings suggest that electrostaticCL/cyt c interactions are central to the initiation of the peroxidase activity, while hydrophobic interactionsare involved when cyt c's tertiary structure is lost. In the presence of CL, cyt c peroxidase activity isactivated at lower H₂O₂ concentrations than for isolated cyt c molecules. This suggests that redistributionof CL in the mitochondrial membranes combined with increased production of H₂O₂ can switch on theperoxidase activity of cyt c and CL oxidation in mitochondria-a required step in execution of apoptosis.