Evidence for H(2)O(2) as the product of reduction of oxygen by alternative oxidase in mitochondria from potato tubers.

Oxygen consumption by alternative oxidase (AOX), present in mitochondria of many angiosperms, is known to be cyanide-resistant in contrast to cytochrome oxidase. Its activity in potato tuber (Solanum tuberosum L.) was induced following chilling treatment at 4 degrees C. About half of the total O(2) consumption of succinate oxidation in such mitochondria was found to be sensitive to SHAM, a known inhibitor of AOX activity. Addition of catalase to the reaction mixture of AOX during the reaction decreased the rate of SHAM-sensitive oxygen consumption by nearly half, and addition at the end of the reaction released nearly half of the consumed oxygen by AOX, both typical of catalase action on H(2)O(2). These findings with catalase suggest that the product of reduction of AOX is H(2)O(2) and not H(2)O, as previously surmised. In potatoes subjected to chill stress (4 degrees C) for periods of 3, 5 and 8 days the activity of AOX in mitochondria increased progressively with a corresponding increase in the AOX protein detected by immunoblot of the protein.