REGULATION OF ALTERNATIVE OXIDASE KINETICS BY PYRUVATE AND INTERMOLECULAR DISULFIDE BOND REDOX STATUS IN SOYBEAN SEEDLING MITOCHONDRIA

Two factors known to regulate plant mitochondrial cyanide-resistant al ternative oxidase activity, pyruvate and the redox status of the enzym e's intermolecular disulfide bond, were shown to differently affect ac tivity in isolated soybean seedling mitochondria. Pyruvate stimulated alternative oxidase activity at low levels of reduced ubiquinone, shif ting the threshold level of ubiquinone reduction for enzyme activity t o a lower value. The disulfide bond redox status determined the maximu m enzyme activity obtainable in the presence of pyruvate, with the hig hest rates occurring when the bond was reduced. With variations in cel lular pyruvate levels and in the proportion of reduced alternative oxi dase protein, a wide range of enzyme activity is possible in vivo.