Determination of molecular mass of the aroid alternative oxidase by radiation-inactivation analysis

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Abstract
The functional molecular mass of the cyanide-resistant salicylhydroxamate-sensitive duroquinol oxidase activity from Symplocarpus foetidus (skunk cabbage) and Sauromatum guttatum spadix mitochondria was determined by radiation-inactivation analysis. The functional molecular mass for the oxidase activity was found to be 26700 Da for skunk cabbage and 29700 Da for Sauromatum guttatum spadix mitochondria frozen at -70.degree. C. Irradiation of dried mitochondrial samples resulted in a larger target size of 38,000 Da, and in some cases, a stimulation of activity from skunk-cabbage and bovine heart mitochondria was also investigated. Dried and frozen mitochondrial samples from both species yielded similar target sizes, in the range 70,900-73,400 Da. Purified bovine heart cytochrome c oxidase was also irradiated, and yielded a functional molecular mass of 66400 Da. The target size of cytochrome c oxidase agrees with literature values insofar as the target size is considerably smaller than the molecular mass of the entire complex.