Halothane metabolism: the dihydrolipoamide acetyltransferase subunit of the pyruvate dehydrogenase complex molecularly mimics trifluoroacetyl-protein adducts.

Monospecific antibodies (anti-CF3CO antibodies), directed against trifluoroacetyl-protein adducts (CF3CO-protein adducts) that are elicited in tissues of experimental animals and humans upon exposure to the anesthetic agent halothane, recognize cross-reactive proteins of 64 and 52 kDa in several tissues of rats and the liver of humans not previously exposed to the drug. These cross-reactive proteins mimic CF3CO-protein adducts. Here, by the use of the anti-CF3CO antibody as an immunoaffinity matrix, the protein of 64 kDa was purified from rat heart microsomal fractions. The amino acid sequence of six internal tryptic peptides exhibited 100% identity with the corresponding deduced amino acid sequences of the dihydrolipoamide acetyltransferase component (E2 subunit) of the rat liver pyruvate dehydrogenase (PDH) complex, as encoded by the cDNA clone pRMIT [Gershwin, M. E., Mackay, I. R., Sturgess, A., & Coppel, R. L. (1987) J. Immunol. 138, 3525-3531]. Lipoic acid, the prosthetic group of the E2 subunit of the PDH complex, exhibited immunochemical properties very similar to those of the hapten-derivative N6-trifluoroacetyl-L-lysine (CF3CO-Lys). On immunoblots, free lipoic acid inhibited the recognition of the E2 subunit, of the not yet identified protein of 52 kDa, and of the bulk of CF3CO-protein adducts by anti-CF3CO antibody with half-maximal inhibitory constants of 0.05, 10.0, and 8.5 mM, respectively. Lipoic acid also abolished the precipitation of the native E2 subunit by anti-CF3CO antibody from solubilized rat heart mitochondrial fractions. These data suggest that lipoic acid is involved in the molecular mimicry of CF3CO-protein adduct-related epitopes by the E2 subunit of the PDH complex.