文摘
Activation of peroxidase catalytic function of cytochrome c (cyt c) by anionic lipids is associatedwith destabilization of its tertiary structure. We studied effects of several anionic phospholipids on theprotein structure by monitoring (1) Trp59 fluorescence, (2) Fe-S(Met80) absorbance at 695 nm, and (3)EPR of heme nitrosylation. Peroxidase activity was probed using several substrates and protein-derivedradicals. Peroxidase activation of cyt c did not require complete protein unfolding or breakage of theFe-S(Met80) bond. The activation energy of cyt c peroxidase changed in parallel with stability energiesof structural regions of the protein probed spectroscopically. Cardiolipin (CL) and phosphatidic acid (PA)were most effective in inducing cyt c peroxidase activity. Phosphatidylserine (PS) and phosphatidylinositolbisphosphate (PIP2) displayed a significant but much weaker capacity to destabilize the protein andinduce peroxidase activity. Phosphatidylinositol trisphosphate (PIP3) appeared to be a stronger inducer ofcyt c structural changes than PIP2, indicating a role for the negatively charged extra phosphate group.Comparison of cyt c-deficient HeLa cells and mouse embryonic cells with those expressing a fullcomplement of cyt c demonstrated the involvement of cyt c peroxidase activity in selective catalysis ofperoxidation of CL, PS, and PI, which corresponded to the potency of these lipids in inducing cyt c'sstructural destabilization.
