NADH oxidase activity of mitochondrial apoptosis-inducing factor

Apoptosis-inducing factor (AIF) is a mitochondrial flavoprotein, which tran slocates to the nucleus during apoptosis and causes chromatin condensation and large scale DNA fragmentation. Here we report the biochemical character ization of AIF's redox activity. Natural AIF purified from mitochondria and recombinant AIF purified from bacteria (AIF Delta1-120) exhibit NADH oxida se activity, whereas superoxide anion (O-2(-)) is formed. AIF Delta1-120 is a monomer of 57 kDa containing 1 mol of noncovalently bound FAD/mol of pro tein. ApoATF Delta1-120, which lacks FAD, has no NADH oxidase activity. How ever, native AIF Delta1-120, apoAIF Delta1-120, and the reconstituted (FAD- containing) holoAIF Delta1-120 protein exhibit a similar apoptosis-inducing potential when microinjected into the cytoplasm of intact cells. inhibitio n of the redox function, by external addition of superoxide dismutase or co valent derivatization of FAD with diphenyleneiodonium, failed to affect the apoptogenic function of AIF Delta1-120 assessed on purified nuclei in a ce ll-free system. Conversely, blockade of the apoptogenic function of AIF Del ta1-120 with the thiol reagent para-chloromercuriphenylsulfonic acid did no t affect its NADH oxidase activity. Altogether, these data indicate that AI F has a marked oxidoreductase activity which can be dissociated from its ap optosis-inducing function.