Mitochondrial antibodies in primary biliary cirrhosis. 3. Characterization of the inner-membrane complement fixing antigen.

The mitochondrial inner-membrane autoantigen reacting with the serum of patients with primary biliary cirrhosis, was purified up to fifty-fold by centrifugal fractionation of sub-mitochondrial fragments obtained by hypotonic swelling and ultrasonication. Respiration and oxidative phosphorylation as well as swelling and contraction were not affected by the presence of the antibody and it could be shown that a number of readily extractable mitochondrial enzymes, and the components of the electron transport chain were not associated with the antigen. The highly purified antigen fraction, although having a vesicular ultrastructure with phospholipid composition characteristic of inner membranes, was nonetheless devoid of cytochrome oxidase activity. Although the exact location of the antigen on the inner membranes is not yet known, it can be physically dissociated from the components of the respiratory chain.