Further purification of the mitochondrial inner membrane autoantigen reacting with primary biliary cirrhosis sera.

The mitochondrial inner membrane autoantigen reacting with sera from patients with primary biliary cirrhosis depends on lipid and protein moieties for complement-fixing activity, but its chemical analysis requires some degree of solubilization. Attemps to achieve this by citraconylation led to anticomplementary effects and inactivation, but treatment with 8 M urea fragmented the membranes sufficiently to allow gel filtration and estimation of its mol. wt at 180,000–200,000. The antigen was further purified by affinity chromatography using Igs from patients with anti-mitochondrial antibodies (AMA) coupled to Sepharose 4B, as immunosorbent. The 8 M urea eluate was about 100 times more active than crude inner membranes and showed a single band on polyacrylamide electrophoresis. Liver and brown fat gave the same band, brown fat having four times the potency of liver. Electron microscopy of the purified antigen from the two organs showed that it reaggregated into membranous vesicles when urea was removed. The purified antigen may be of use if an automated radioimmunoassay were to prove sensitive and specific for the detection of AMA as this antibody is an important marker for `autoimmune' chronic liver disorders.