Characterization of the dihydrolipoamide acetyltransferase of the mitochondrial pyruvate dehydrogenase complex from potato and comparisons with similar enzymes in diverse plant species

The pyruvate dehydrogenase complex (mPDC) from potato (Solanum tuberosum cv . Romano) can be disassociated in 1 M NaCl and 0.1 M glycine into a large d ihydrolipoamide acetyltransferase (E2) complex and smaller pyruvate dehydro genase (El) and dihydrolipoamide dehydrogenase (E3) complexes. The E2 compl ex consists of 55 and 78-kDa polypeptides which are reversibly radiolabelle d to a similar degree in the intact mPDC by [2-C-14]pyruvate. Affinity-puri fied antibodies against the 55-kDa protein do not cross-react with the 78-k Da protein and the two proteins show different peptide patterns following p artial proteolysis. The 78 and 55-kDa proteins are present in approximately equal abundance in the E2 complex and incorporate a similar amount of [C-1 4] on incubation with [2-C-14]pyruvate. Native mPDC and the E2 complex have sedimentation coefficients of 50S and 30S, respectively. Titration of elec tro-eluted polypeptides against the intact mPDC and E2 complex revealed tha t each mg of mPDC contains 0.4 mg of E1, 0.4 mg of E2 and 0.2 mg of E3. Lab elling of partially purified mPDC from potato, pea, cauliflower, maize and barley, with [2-C-14]pyruvate, suggest that a 78-kDa acetylatable protein i s only found in the dicotyledonous species, while all plant species tested contained a smaller 52-60 kDa acetylatable protein.