Immunoextraction of lipoamide dehydrogenase from cultured skin fibroblasts in patients with combined α-ketoacid dehydrogenase deficiency

Combined deficiency of the pyruvate, α-ketoglutarate and branched-chain keto acid dehydrogenase complexes is a rare condition in which activity of lipoamide dehydrogenase is either reduced or grossly deficient. Activities in three cell strains from patients with excretion of branched chain ketoacids and α-ketoglutarate and lactic-acidemia showed decreased levels of the three α-ketoacid dehydrogenases. Lipoamide dehydrogenase activity was 5% of normal in one cell stain and 50-60% in the other two. Antiserum raised against lipoamide dehydrogenase was used to immunoprecipitate labelled lipoamide dehydrogenase from fibroblasts grown on [³⁵S]methionine. After separation of cell proteins from control fibroblasts by sodium dodecyl sulphate polyacrylamide gel electrophoresis and fluorography, a prominent 55 kilodalton band was evident in cell extracts treated with the antiserum which corresponded to lipoamide dehydrogenase. In the cell lines from patients with combined α-ketoacid dehydrogenase deficiency immunoprecipiation of lipoamide dehydrogenase showed that this protein was present in similar amounts to that seen in control cell lines and was also of the correct molecular weight.