[Detection of porin in inter-mitochondrial contacts]

The binding of monoclonal antibodies (mAb) to the N-terminal part of VDAC with freshly isolated, unfixed rat heart mitochondria has been studied. It was established that mAb do not react with the main portion of the mitochondria. At the same time, successful binding to some of those was observed. Gold particles were organized, as a rule in three types of clusters: (i) thread-like clusters; (ii) small, irregularly shaped clusters, and (iii) big clusters covering the greater part of the mitochondrial surface. In the region of tight junctions between mitochondria, specific binding of mAb to mitochondrial VDAC, such as thread-like and small clusters, was found. In some cases, antibody clusters were localized in the region which separates two mitochondrial compartments differing in configuration of the cristae. When the outer mitochondrial membrane was partially stripped off, this membrane was extensively labelled by antibodies. It is concluded that the N-terminus of porin is localized on the inner surface of the outer mitochondrial membrane, so that some damage of the outer membrane appears to be required to allow the N-terminal porin antibody to contact the antigenic determinant. Such a damage is apparently more probable in the place of contacts of two mitochondria or two mitoplasts covered by the common outer membrane. In any case, the data obtained strongly suggest that porin is present in the junction region.