Together with BCKDHB forms the heterotetrameric E1 subunit of the mitochondrial branched-chain alpha-ketoacid dehydrogenase (BCKD) complex. The BCKD complex catalyzes the multi-step oxidative decarboxylation of alpha-ketoacids derived from the branched-chain amino-acids valine, leucine and isoleucine producing CO2 and acyl-CoA which is subsequently utilized to produce energy. The E1 subunit catalyzes the first step with the decarboxylation of the alpha-ketoacid forming an enzyme-product intermediate. A reductive acylation mediated by the lipoylamide cofactor of E2 extracts the acyl group from the E1 active site for the next step of the reaction. {ECO:0000269|PubMed:10745006, ECO:0000269|PubMed:7883996, ECO:0000269|PubMed:9582350}. This is the function of Ensembl gene identifier ENSG00000248098 (BCKDHA, branched chain keto acid dehydrogenase E1 subunit alpha).