Tissue specific isoforms of an enzyme autoantigen were sought in an attempt to explain a possible disease-associated translocation of the enzyme. A human heart cDNA clone (0.66 kb) coding for part of the lipoate acetyl transferase component of pyruvate dehydrogenase complex, recently identified as one of the major autoantigens of primary biliary cirrhosis was isolated. The cloned cDNA corresponded to nucleotides 1545-2201 of a previously published placental sequence, but showed some differences which give rise to differences in the inferred amino acid sequences of proteins. This may indicate the existence of tissue-specific isoforms of the lipoate acetyl transferase component of pyruvate dehydrogenase complex coded for by a multi-gene family.