Protein import into plant mitochondria: precursor proteins differ in ATP and membrane potential requirements

The import pathways of the alternative oxidase and the F(A)d subunit of the ATP synthase from soybean were characterised. The F(A)d precursor does not require extramitochondrial ATP for import and this was shown to be a chara cteristic of the mature protein. The alternative oxidase and F(A)d precurso rs were shown to differ in their requirement for a membrane potential. The membrane potential was modified using malonate, a competitive inhibitor to complex II. The alternative oxidase could be imported at higher malonate co ncentrations compared to the F(A)d. This difference could not be ascribed t o the number of positive charges in each presequence as would be predicted from similar studies in fungi.