Characterization of the preprotein translocase of the outer mitochondrial membrane by blue native electrophoresis.

The mitochondrial outer membrane contains import receptors for nuclear-encoded preproteins and a general import pore responsible for membrane translocation of preproteins. Receptors and the general import pore have been suggested to assemble into a loose complex. However, biochemical characterization of the complex has been limited so far. We report that blue native electrophoresis separates two complexes. One complex of approximately 400 kDa contains the receptor Tom22 and the general import pore component Tom40, the other complex of approximately 120 kDa contains the receptor Tom70. A preprotein accumulated at the general import pore apparently co-migrates with the larger complex, suggesting the functionality of the complex. We conclude that the translocase of the outer membrane consists of at least two subcomplexes and that blue native electrophoresis will be a powerful tool for biochemical analysis of the complexes.