Characterization of the Import Pathway of the FAd Subunit of Mitochondrial ATP Synthase into Isolated Plant Mitochondria

The synthetic precursor of the FAd subunit of mitochondrial ATP synthase was imported into isolated soybean cotyledon mitochondria. Import of the FAd precursor was accompanied by processing to a lower molecular weight mature form. The FAd precursor displayed the following import characteristics not seen before with plant mitochondria: efficient import in the absence of external ATP and import of wheat germ-translated precursor. Pretreatment of the FAd precursor with NEM did not inhibit import. Taken together with the lack of a requirement for external ATP, this indicates that this precursor does not require extramitochondrial ATP-dependent factors for import. Binding studies indicated that the FAd precursor bound to a proteinaceous component of the mitochondrial outer membrane. Inhibitor studies indicated that processing was most likely via the general mitochondrial processing peptidase. The results suggest that import of this subunit occurs via a pathway different from the general import pathway described for the majority of precursor proteins.