The sites of superoxide anion generation in higher plant mitochondria

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Abstract

A variety of higher plant mitochondria and submitochondrial particles with varying degrees of cyanide insensitivity have been examined for their possible Superoxide anion generating capacity. It was found that neither the cytochrome oxidase nor the alternative oxidase pathways produced significant quantities of Superoxide anions. All preparations examined generated Superoxide anions to a small extent with NADH as respiratory substrate, but almost negligibly with succinate as respiratory substrate. A component of the NADH-supported activity was insensitive to cyanide, antimycin A, and salicylhydroxamic acid. Hence most of this activity is attributed to direct reduction of oxygen by the flavoprotein NADH dehydrogenases. The remainder may be caused by oxygen reduction in the ubiquinone-cytochrome b region of the chain. In some plant mitochondria and submitochondrial particles, a contaminating tyrosinase activity, which can catalyze the oxidation of epinephrine by molecular oxygen, causes a very large interference in Superoxide anion determinations. Methods of distinguishing and measuring these various activities are discussed.

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