Molecular cloning of the mature E1b-β subunit of human branched-chain α-keto acid dehydrogenase complex

We have isolated a cDNA encoding the E1b-β subunit of the human branched-chain α-keto acid dehydrogenase complex. The human E1b-β cDNA is 1401 base pairs in length. It encodes the entire mature E1b-β subunit consisting of 342 amino acid residues, and a mitochondrial targeting presequence of 31 residues. The calculated molecular mass of the mature human E1b-β subunit is 37 851 Da, and the calculated isoelectric point is pH 5.18. A hydropathy plot shows that the human E1b-β subunit is highly hydrophobic. Northern blot analysis shows that the human E1b-β mRNA is approximately 1.4 kb in size. It is present at the normal level in fibroblasts from two unrelated maple syrup urine disease patients.