STUDIES ON THE IMPORT AND PROCESSING OF THE ALTERNATIVE OXIDASE PRECURSOR BY ISOLATED SOYBEAN MITOCHONDRIA

Import of the synthetic precursor of the alternative oxidase from soyb ean was shown to be dependent on a membrane potential and ATP. The mem brane potential in soybean mitochondria may be formed either by respir ation through the cytochrome pathway, or through the alternative oxida se pathway with NAD(+)-linked substrates. Import of the alternative ox idase precursor in the presence of succinate as respiratory substrate was inhibited by KCN. Import in the presence of malate was insensitive to KCN and SHAM added separately, but was inhibited by KCN and SHAM a dded together (inhibitors of the cytochrome and alternative oxidases r espectively). Import of the alternative oxidase was accompanied by pro cessing of the precursor to a single 32 kDa product in both cotyledon and root mitochondria. This product had a different mobility than the two alternative oxidase bands detected by immunological means (34 and 36 kDa), suggesting that the enzyme had been modified in situ. When th e cDNA clone of the alternative oxidase was modified by a single mutat ion (-2 Arg changed to -2 Gly), the processing of the precursor was in hibited.