Direct observation of release of cytochrome c from lipid-encapsulated protein by peroxide and superoxide: A possible mechanism for drug-induced apoptosis

Release of cytochrome c from inside lipid vesicles and from inside proteoli posomes formed by cytochrome c oxidase has been studied by spectrophotometr ic methods. The protein encapsulated inside vesicles did not form complex w ith sodium azide solution added externally. Both hydrogen peroxide and supe roxide were found to cause release of cytochrome c from the lipid encapsula ted protein, which was detected from the distinct spectral changes due to t he formation of the azide complex of cytochrome c in th solution. Cytochrom e c encapsulated inside proteoliposomes containing cytochrome c oxidase (Cc O) did not release the cytochrome c during enzymatic turnover of CcO. The a nticancer drug, doxorubicin, was found to inhibit the biochemical function of cytochrome c oxidase and release of cytochrome c was observed from the p roteoliposome encapsulating the protein during the enzymatic turnover in th e presence of doxorubicin. The results indicated that the inhibition of enz ymatic activity by doxorubicin possibly leads to the formation of reactive oxygen species, which induce the release of cytochrome c from inside to out side of the membrane. (C) 2001 Academic Press.