On the impermeability of the outer mitochondrial membrane to cytochromec : II. Studies on isolated membrane fragments.

Outer mitochondrial membranes isolated by the swelling-shrinkage sonication procedure of Sottocasaet al. [19, 20] forms small sealed vesicles. If cytochromec is present during the procedure it is trapped inside these vesicles and can not be washed out nor is accessible to external enzymes, e.g., cytochrome oxidase (EC 1.9.3.1) or succinate-cytochromec reductase present as contamination by the inner membrane, but is fully accessible to rotenone-insensitive NADH-cytochromec reductase of the outer membrane. This indicates the impermeability of the outer mitochondrial membrane to cytochromec.A modification of the original procedure for the separation of the outer mitochondrial membrane is described.