Journal
BIOCHEMISTRY
Volume 45, Issue 15, Pages 4998-5009Publisher
AMER CHEMICAL SOC
DOI: 10.1021/bi0525573
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- NHLBI NIH HHS [R01 HL070755, HL61411, R01 HL061411, R01 HL070755-02] Funding Source: Medline
- NIAID NIH HHS [U19 AI068021, U19 AI068021-010002] Funding Source: Medline
- NIOSH CDC HHS [OH 008282] Funding Source: Medline
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During apoptosis, cytochrome c (cyt c) is released from intermembrane space of mitochondria into the cytosol where it triggers the caspase-dependent machinery. We discovered that cyt c plays another critical role in early apoptosis as a cardiolipin (CL)-specific oxygenase to produce CL hydroperoxides required 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 fluorescence and absorbance at 695 nm (Fe-S(Met(80)) band). The peroxidase activity increase preceded the loss of protein tertiary structure. Monounsaturated tetraoleoyl-CL (TOCL) induced peroxidase activity and unfolding of cyt c more effectively than saturated tetramyristoyl-CL (TMCL). TOCL/cyt c complex was found more resistant to dissociation by high salt concentration. These findings suggest that electrostatic CL/cyt c interactions are central to the initiation of the peroxidase activity, while hydrophobic interactions are involved when cyt c's tertiary structure is lost. In the presence of CL, cyt c peroxidase activity is activated at lower H2O2 concentrations than for isolated cyt c molecules. This suggests that redistribution of CL in the mitochondrial membranes combined with increased production of H2O2 can switch on the peroxidase activity of cyt c and CL oxidation in mitochondria-a required step in execution of apoptosis.
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